[Federal Register Volume 71, Number 234 (Wednesday, December 6, 2006)]
[Proposed Rules]
[Pages 70717-70733]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E6-20530]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding
on a Petition To List the Cerulean Warbler (Dendroica cerulea) as
Threatened With Critical Habitat
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of a 12-month petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
12-month finding on a petition to list the cerulean warbler (Dendroica
cerulea) as threatened under the Endangered Species Act of 1973, as
amended (Act). The petition also asked that critical habitat be
designated for the species. After reviewing the best available
scientific and commercial information, we find that the petitioned
action is not warranted. We ask the public to submit to us any new
information that becomes available concerning the status of, or threats
to, the species. This information will help us monitor and encourage
the conservation of this species.
DATES: The finding announced in this document was made on November 28,
2006.
ADDRESSES: Comments and materials received, as well as supporting
documentation used in the development of this 12-month finding, will be
available for inspection, by appointment, during normal business hours
at the Columbia Ecological Services Field Office, 101 Park DeVille
Drive, Suite A, Columbia, Missouri 65203. Submit new information,
materials, comments, or questions concerning this species to the
Service at the above address.
FOR FURTHER INFORMATION CONTACT: Charles Scott, Supervisor (see
ADDRESSES), by telephone at 573-234-2132, by facsimile at 573-234-2181,
or by electronic mail at [email protected]. Individuals who are
hearing-impaired or speech-impaired may call the Federal Relay Service
at 1-800-877-8339 for TTY assistance.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Endangered Species Act of 1973, as
amended (16 U.S.C. 1531 et seq.), requires that, for any petition to
revise the Lists of Endangered and Threatened Wildlife and Plants that
contains substantial scientific or commercial information that the
petitioned action may be warranted, we make a finding within 12 months
of the date of the receipt of the petition on whether the petitioned
action is: (a) Not warranted, (b) warranted, or (c) warranted, but that
the immediate proposal of a regulation implementing the petitioned
action is precluded by other pending proposals to determine whether any
species is threatened or endangered, and expeditious progress is being
made to add or remove qualified species from the List of Endangered and
Threatened Species. Such 12-month findings are to be published promptly
in the Federal Register. Section 4(b)(3)(C) of the Act requires that a
petition for which the requested action is found to be warranted but
precluded shall be treated as though resubmitted on the date of such
finding, requiring a subsequent finding to be made within 12 months.
Previous Federal Actions
We added the cerulean warbler to our former Category 2 list of
candidate species on November 21, 1991 (56 FR 58804). Category 2
candidate species were those species for which we possessed data
indicating that proposing to list them as endangered or threatened was
possibly appropriate, but for which conclusive data on biological
vulnerability and threat were not available at that time to support
proposed rules. Category 1 candidate species were those for which we
[[Page 70718]]
possessed sufficient information on biological vulnerability and
threats to support proposals to list them as endangered or threatened
species. The cerulean warbler was also in the November 15, 1994,
Candidate Notice of Review (59 FR 58982) as a Category 2 candidate
species. The list of Category 2 species was eliminated by the Service
in 1996. Since then the Service has applied the term ``candidate
species'' only to those species previously considered to be ``Category
1'' candidates, and we apply the same definition to these species (61
FR 7596; February 28, 1996). The cerulean warbler has never been a
Category 1 candidate species or a candidate species, as defined, since
1996.
Due to concerns regarding the population trend of the species, in
1995, the Service contracted to Dr. Paul Hamel, of the U.S. Forest
Service's Southern Forest Research Station in Stoneville, Mississippi,
to develop a cerulean warbler rangewide status assessment report. Dr.
Hamel completed his report in April of 2000 (Hamel 2000a), and we
distributed it and posted it on our Web site at that time.
On November 6, 2000, the Service received an October 30, 2000,
letter from Douglas A. Ruley of the Southern Environmental Law Center
in Asheville, North Carolina. Mr. Ruley's letter conveyed a petition to
list the cerulean warbler as a threatened species and to designate
critical habitat for the species (Ruley 2000). The following
organizations were listed as the petitioners: National Audubon Society,
Defenders of Wildlife, Sierra Club, The Wilderness Society, American
Lands Alliance, Western North Carolina Alliance, Southern Appalachian
Biodiversity Project, Appalachian Voices, Cherokee Forest Voices,
Southern Environmental Law Center, Southern Appalachian Forest
Coalition, Heartwood, Dogwood Alliance, West Virginia Highlands
Conservancy, Inc., Virginia Forest Watch, Buckeye Forest Council,
Allegheny Defense Project, Vernon Civic Association, Conservation
Action Project, Superior Wilderness Action Network, Indiana Forest
Alliance, Regional Association of Concerned Environmentalists, Ouachita
Watch League, Newton County Wildlife Association, Chattooga
Conservancy, Wild Alabama, Georgia Forest Watch, and South Carolina
Forest Watch.
On September 24, 2002, the Service made its initial 90-day finding
on the petition, and a notice of that finding was published in the
Federal Register on October 23, 2002 (67 FR 65083). Our finding was
that the petition presented substantial information indicating that the
petitioned action of listing the species may be warranted. At that
time, we initiated a status review, which included a 90-day comment
period.
We received 290 responses to our request for additional information
in our 90-day finding for the cerulean warbler (67 FR 65083; October
23, 2002). A large number of these responses were identical or similar
comments. Comments and information were received from 12 State fish and
wildlife agencies within the range of the warbler, 4 academic
researchers, 2 county government agencies, the U.S. Forest Service (4
units), National Park Service (2 units), Department of Defense, U.S.
Army Corps of Engineers, a U.S. Congressman, 7 corporations, 40
nongovernmental organizations, numerous private citizens, and several
other entities. Additionally, we directly contacted, and received
information from, wildlife agencies and biologists within the cerulean
warbler's range in Canada and South America. We reviewed all responses
received, and those that contained new, updated, or additional
scientific or commercial data were thoroughly considered in this 12-
month finding.
Due to budget shortfalls during subsequent fiscal years, the
Service was unable to fund additional work on the petition until late
in fiscal year 2005. Since that time, we have analyzed the comments
received after the 2002 finding, reviewed new published and unpublished
reports and data on the species and factors affecting its habitat, and
brought together a panel of experts on the species to provide
additional insight into the current status and trends of the cerulean
warbler.
After our resumption of work on the petition in late 2005, a
lawsuit was filed by five of the petitioners (National Audubon Society,
Defenders of Wildlife, Southern Appalachian Biodiversity Project,
Western North Carolina Alliance, and Heartwood) in the U.S. District
Court for the District of Columbia on February 28, 2006. The suit asked
the Court, among other things, to compel the Service to make and
publish in the Federal Register a 12-month finding regarding the
plaintiffs' petition to list the cerulean warbler as a threatened
species. Although we had already resumed work on the petition, due to
the lawsuit, we entered into a settlement agreement with plaintiffs in
which we agreed to provide our 12-month finding to the Federal Register
no later than November 30, 2006.
Cerulean Warbler Natural History
The cerulean warbler is a small insectivorous neotropical migrant
songbird (11.5 centimeters (4.5 inches) long and weighing 8 to 10 grams
(0.3 to 0.4 ounces)). It breeds in mature deciduous forests primarily
within the central hardwood region of eastern North America, primarily
in the Ohio and Mississippi River Valleys and adjacent areas east of
the Appalachians, in New England and southern Canada, and in the Great
Lakes region. (Hamel 2000a, pp. 2-4). The breeding range generally
extends from the eastern Great Plains, north to Minnesota, east to
Massachusetts, and south to North Carolina and Louisiana (Hamel 2000a,
p. 2), encompassing 33 States and 2 Canadian Provinces. The core area
of the breeding range is currently within the Cumberland Plateau and
Ohio Hills physiographic regions in eastern Tennessee, eastern
Kentucky, southern and western West Virginia, southeastern Ohio, and
southwestern Pennsylvania (Villard and Mauer 1996, p. 7 and Figure 7;
Sauer et al. 2005a). This species undertakes a long migration compared
to many other warblers and passerines of similar size (Hamel 2000b, p.
1), covering a distance of approximately 4,000 kilometers (km) (2,500
miles (mi)) between the central latitudes of North America and northern
latitudes of South America. The migratory pathway between the breeding
and wintering grounds is not well known, but for most individuals, it
likely includes a flight across the Gulf of Mexico and stops at a
limited number of locations in Central America and northern Colombia or
Venezuela (Hamel 2000b, p. 4). The fall migration to South America
might be along a more easterly path than that of the northward
migration in the spring (Dunn and Garrett 1997, p. 405). Cerulean
warblers winter in broad-leaved evergreen forests within a relatively
narrow band of middle elevations (500 to 1,800 meters (m); 1,650 to
5,900 feet (ft)) in the northern Andes Mountains in Venezuela,
Colombia, Ecuador, Peru, and Bolivia and possibly in the Guayana
Highlands of southeastern Venezuela, especially the tabletop mountains
(tepuis) of this ecoregion (Robbins et al. 1992, p. 559; Moreno et al.
2006 unpublished report, p. 3).
On the breeding grounds, cerulean warblers prefer mature hardwood
forests with tall, large-diameter trees and a structurally diverse
canopy (multiple vegetation layers, often associated with uneven-aged
forest stands). They occupy forests with these structural
characteristics in both upland and
[[Page 70719]]
bottomland locations (Hamel 2000b, p. 4). In the Appalachian Mountains,
they tend to occur more frequently and in higher abundance on ridge
tops than in valley bottoms (Weakland and Wood 2005, pp. 503-504; Wood
et al. 2006, pp. 160-161; Buehler et al. in press, p. 9). Throughout
much of their breeding range, they prefer to breed in large forest
patches, and so are considered ``area-sensitive'' (Robbins et al.
1989a, p. 25; Mueller et al. 2000, p. 15), although they might not be
as sensitive to forest patch size in well-forested and less fragmented
landscapes where avian nest predation and parasitism rates tend to be
lower (Hamel 2000b, p. 4). In parts of their range, cerulean warblers
exhibit positive associations with canopy gaps and relatively small
internal forest openings (Perkins 2006, p. 26), but they avoid abrupt
edges between forest and large areas of open land (Wood et al. 2006, p.
160). Post-fledging habitat for this species has not been studied, but
assuming cerulean warblers are similar to other mature forest-
associated birds, they might seek out areas where shrubby vegetation
provides good cover from predators as well as an abundance of good
foraging substrate. Such areas might include small forest openings or
early successional habitats, but habitat use during this period of the
year has not been described and the relative importance of different
habitat types during the post-fledging period is not known.
Insects are the primary food source of cerulean warblers throughout
the year. During the breeding season, their diet has been observed to
consist primarily of Homoptera and Lepidoptera but also may include
small amounts of Coleoptera, Hymenoptera, Diptera, Hemiptera, Araneae,
and other arthropods (Hamel 2000b, p. 6). While no detailed studies of
diet have been completed during the non-breeding period, cerulean
warblers appear to use nectar resources, as well as insects, during at
least some period of their residency on their non-breeding grounds in
South America (Jones et al. 2000, p. 961; USFWS 2006, Appendix 5--M.I.
Moreno's PowerPoint presentation, slide 15) and have also been observed
eating small amounts of plant material during migration (Hamel 2000b,
p. 5). Their primary foraging mode for capturing insects is gleaning
prey from the upper and lower surfaces of leaves. They also use
sallying and hover-gleaning to a lesser extent (Hamel 2000b, p. 5).
Cerulean warblers build their nests high above ground (mean height
of 11.4 m (37 ft); Hamel 2000b, p. 9) in the mid-story or canopy of
trees. Clutch size is normally 3 or 4 eggs with an incubation period of
11 to 12 days and a nestling period of 10 to 11 days. Their nests are
known to be parasitized by brown-headed cowbirds, particularly in the
western portion of the cerulean warbler breeding range where cowbirds
are more abundant (Hamel 2000b, pp. 9-11). Nest success varies annually
and regionally, with observed average annual nest success rates at
specific study sites ranging from approximately 20 percent in southern
Indiana and the lower Mississippi River valley to approximately 58
percent in Ontario and eastern Tennessee. The average number of young
fledged per successful nest also varies, although somewhat less
dramatically, with reports of annual values between 1.7 and 3.0 for
most study sites (USFWS 2006, Appendix 5--D. Buehler's PowerPoint
presentation, slides 25-28). Cerulean warblers typically arrive on
their breeding grounds between mid-April and mid-May, depending on
latitude, and remain there until sometime between late July and mid-
September (Dunn and Garrett 1997, pp. 405-406). Cerulean warblers
usually raise a single brood during this period; multiple nesting
attempts are commonly undertaken if initial nest attempts fail. It is
rare for this species to raise two broods in the same breeding season.
Cerulean warblers are predominantly socially monogamous (one male
mated with one female), but social bigamy (one male mated with two
females) has been observed in the Ontario population (USFWS 2006,
Appendix 4, Day 2-p. 2). This behavior has not been studied at other
locations. Some researchers have also observed a clumped distribution
of cerulean warbler territories within study sites, apparently
independent of habitat features. However, these patterns have not been
studied rigorously nor confirmed as being different from a random
distribution or a result of habitat selection (Hamel 2000b, p. 8).
Analysis of genetic variability at the population level has
revealed no significant variation in neutral genetic markers across the
breeding range, suggesting a single genetic population for this species
(Veit et al. 2005, pp. 165-166). A study of natal and breeding
dispersal between years using stable isotope analysis corroborates this
hypothesis by suggesting a relatively high level of interannual adult
dispersal between regions, particularly within the central portions of
the breeding range (USFWS 2006, Appendix 4, Day 1--p. 14). Adult
dispersal to different breeding locations between years appears to be
lower in both the southern and northern portions of the range than in
the center of the range, suggesting higher site fidelity to breeding
locations in those portions of the range. Natal dispersal between
regions within the breeding range did not appear to be any more
pronounced than adult dispersal. This is different than many other
warbler species, which typically exhibit much higher natal dispersal
than adult dispersal. Dispersal characteristics of cerulean warblers
probably influence source-sink dynamics of the population, and more
information on dispersal is needed to understand the current population
trend of the species.
On the wintering grounds, this species may prefer forests with old-
growth conditions, but it has also been found in second-growth forests
and shade-grown coffee plantations (Hamel 2000b, p. 5; Jones et al.
2000, p. 958). As with its breeding habitat, a structurally diverse
canopy with multiple vegetation layers appears to be an important
component of its wintering habitat. It is generally found in mixed-
species flocks of canopy-dwelling birds, and this association with
mixed-species flocks could be an important characteristic of their
occurrence on the wintering grounds (Hamel 2000b, p. 5), although more
study of their social behavior is needed. Cerulean warblers usually
reside on their winter grounds from October to February (Hamel 2000b,
p. 9--Figure 3).
Cerulean warblers are nocturnal migrants. Little is known about
habitat preferences and other ecological aspects of this bird's
migration. Several stop-over locations for spring migration have been
found in Belize (Parker 1994, p. 70), Honduras, and Guatemala (Welton
et al. 2005, p. 1), but records of this species during migration
elsewhere are scarce. To explain this, one hypothesis is that cerulean
warblers could migrate in pulses of large groups of individuals that
make relatively long flights between stops (for example, northern South
America to middle Central America and then across the Gulf of Mexico to
southern United States). Even fewer records exist for cerulean warblers
during the southward migration in the fall, prompting the suggestion
that these birds might fly non-stop from the southern U.S. all the way
to the northern coast of South America. Isotope analyses indicate some
level of migratory connectivity for this species (USFWS 2006, Appendix
4, Day 2--pp. 7-8), suggesting that individuals residing in the
northern portions of the breeding range tend to go to more northerly
portions of the wintering range and birds from the southern portions of
the breeding range go to the
[[Page 70720]]
more southerly portions of the wintering range.
Survival rates of cerulean warblers have not been studied widely
across their range. Only one study has published estimates of minimum
survival rates. Jones et al. (2004, p. 17) reported an annual adult
male survival rate of 0.49 over the period 1995 to 2001; or 0.54 in
``normal years'' and 0.40 following an ice storm in 1998. These
estimates are minimum values because they do not account for adult
dispersal and emigration between breeding seasons.
Population Size and Trends
Background
Since its inception in 1966, the North American Breeding Bird
Survey (BBS) is the primary data source for estimating population
trends of more than 400 species of birds breeding in North America
(Droege 1990, p. 1). More than 4,000 BBS survey routes are distributed
along secondary roads across the United States and southern Canada in a
stratified random design. Each year, volunteer observers count birds
along these routes, following standardized protocols. Surveys are
conducted at approximately the same time each year, which is typically
during the first half of June in most locations. Each survey route
consists of 50 stops spaced 0.8 km (0.5 mi) apart. Observers count all
the birds seen and heard within 0.4 km (0.25 mi) of each stop location
during a three-minute period (Droege 1990, p. 1). The sum of the counts
for each species over the 50 stops is used as an index of relative
abundance for that route (Link and Sauer 2002, pp 2833).
Statistical analyses are performed on these index values across
routes to estimate population trends for particular species or groups
of species. Two statistical analysis techniques are currently employed
by analysts working with the BBS data: The route-regression method
(Geissler and Sauer 1990, pp. 54-56) and the hierarchical model method
(Link and Sauer 2002, pp. 2,833-2,836). The hierarchical model method
is the more recently developed method, and BBS analysts are in
transition from using the route-regression method to using primarily
the hierarchical model method, which is a less subjective and more
efficient method for estimating trend (Link and Sauer 2002, p. 2,837).
The presentation of BBS data in the 2000 petition (Ruley 2000) used the
route-regression method. Throughout this finding we discuss BBS data
using the newer hierarchical model method. As a result, the figures
used herein to describe BBS population trends differ from those used in
the petition. Statistical analyses can be conducted across different
time frames and spatial scales (for example, States, bird conservation
regions, range-wide).
It is important to recognize that the BBS was designed to estimate
trends (changes in population) and not actual abundance (population
size) of birds. Much of the criticism that has been leveled at the
BBS--including doubts expressed about the BBS in the Service's positive
90-day finding on the petition to list the cerulean warbler--stems from
confusion about the survey's objective and the protocols required to
meet that objective. The following discussion addresses four aspects of
the BBS that contribute to this confusion and why these issues do not
detract from the usefulness of BBS for tracking bird population trends.
(1) The point count survey methodology of the BBS does not result
in a complete count of the birds present. The efficiency with which
birds are counted varies between observers and within observers over
time and space. In addition, a 3-minute count is not long enough to
detect all birds present in a given location due to temporal
variability (both daily and seasonally) in detectability of different
species. However, the BBS methodology does provide an index of relative
abundance of birds along the survey routes. This index can be scaled to
different levels of abundance using different analysis methods and
provides an appropriate means for assessing population change along the
routes. An index of relative abundance is suitable for tracking changes
in the size of the entire population if the ratio between the number of
birds detected in the surveys and number of birds actually present
across the landscape remains fairly constant and without any
directional bias across years (Bart et al. 1998, pp. 212-214).
The statistical analyses of BBS data help to address some of the
limitations pertaining to observer efficiency by incorporating
variables that account for observer effects into the analyses. Such
effects as differences in counts between observers in different years
on the same route or the differences between an observer's first count
and counts in subsequent years on the same route (the novice effect)
are accounted for in the statistical analysis of the survey data (Sauer
et al. 1994, pp. 59-60; Link and Sauer 2002, p. 2,834).
Another factor contributing to incomplete counts of all the birds
present is that most detections of forest-associated songbirds are
largely through observers hearing the songs of males. Females of most
forest songbirds do not sing and, therefore, are more difficult to
detect during the breeding season. Thus, females of these species are
greatly undersampled by the BBS. Again, this limitation is not relevant
to the detection of population trends as long as trends in the male
portion of the population are representative of trends in the entire
population. For most small songbirds, such as the cerulean warbler,
there is no substantial data indicating either a highly skewed sex
ratio or a large difference in survival rates between the sexes such
that trend data might be biased.
(2) BBS surveys are conducted along roadsides and might not
accurately reflect habitats across entire landscapes. The proportion of
different habitat types could be different across landscapes compared
with what is sampled by BBS routes. However, this limitation, in and of
itself, does not render the BBS ineffective in estimating trends of
forest birds unless there is a consistent bias in the rate of change of
habitats bordering roads compared to change of habitats away from
roadsides. The fact that birds that avoid habitat edges might not be as
abundant near roads as away from roads also does not influence trend
estimates, except perhaps to reduce overall sample size for such
species and require more years of data or more detections to achieve
appropriate levels of statistical significance.
Experimental studies comparing roadside with off-road counts or
modeling efforts to assess relative amounts of different habitats in
the areas immediately surrounding BBS survey routes and areas away from
routes are necessary to address the issue of roadside habitat bias for
the BBS. Two published studies have evaluated the bias associated with
roadsides in the eastern United States. These studies were conducted in
Ohio and Maryland. They both concluded that, although BBS routes under-
sampled forest habitats in the regions evaluated (areas adjacent to BBS
routes tended to have proportionately less forest cover than did the
region as a whole), they did not find a bias in the change in habitats
over time along BBS roadside routes compared with the larger landscapes
surrounding those routes (Bart et al. 1995, p. 760; Keller and Scallan
1999, pp. 53-55). These studies suggest that the roadside nature of the
BBS does not create a substantial bias in the BBS data pertaining to
habitat changes that are likely to influence bird population trends. In
contrast with this apparent lack of bias in trend estimates, the
indication from these studies that BBS routes might under-sample forest
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habitats in the East could have implications for the population size
estimates based on the Partners in Flight method (discussed below).
However, an unpublished study from West Virginia (Weakland et al. 2003,
p. 8) found no significant difference between the abundance estimates
of cerulean warblers from off-road counts and from BBS routes. The
study found a tendency for the off-road counts to be higher than counts
on BBS routes, but the difference was not significant. The study
concluded that, for cerulean warblers, data collected on BBS routes in
West Virginia are comparable to data collected from off-road locations
(Weakland et al. 2003, p. 8).
In the positive 90-day finding on the petition to list the cerulean
warbler, the Service expressed doubt on the ability of BBS data to
reliably determine bird population trends of mature forest-associated
species, such as the cerulean warbler. Reasons for this doubt were
primarily associated with concerns about a possible roadside bias and
concerns about lack of uniform coverage of BBS routes across the range
of the cerulean warbler. To date, the published evidence on the topic
of the roadside bias suggests that the roadside nature of the BBS does
not significantly bias its ability to accurately track population
trends of mature forest species, such as cerulean warblers (Bart et al.
1995, p. 760; Keller and Scallan 1999, pp. 53-55). Furthermore, the
more recently implemented hierarchical model method for analyzing BBS
data estimates trends more efficiently (resulting in smaller confidence
intervals around the trend estimate) based on the available data (Link
and Sauer 2002, p. 2837), reducing concerns about lack of uniformity in
coverage of BBS routes, particularly at the rangewide scale.
It is also worth noting that efforts to compare population trends
calculated from BBS data with independent data sources have
corroborated the trends indicated by the BBS for a variety of species,
including independent trends based on the Christmas Bird Count,
Mourning Dove Survey, raptor migration counts, and checklist programs
(Droege 1990, p. 3). In addition, many peer-reviewed publications have
been completed using BBS data (for example, Robbins et al. 1989b, Sauer
et al. 1994, Link and Sauer 1997, Link and Sauer 1998, Royale et al.
2002, Sauer and Link 2002), indicating the overall robustness and
scientific credibility of the BBS and its utility for monitoring bird
population trends.
(3) A published analysis of BBS data using the hierarchical model
method indicates that at the range-wide level, cerulean warblers have
declined at an average rate of 3.04 percent per year during the period
of 1966 to 2000, with the 95 percent credible interval (confidence
interval for hierarchical method; C.I.) for the trend estimate being -
4.02 to -2.07 (Link and Sauer 2002, p. 2837). A more recent, but
unpublished, analysis of the BBS data for the years 1966 to 2005 using
the hierarchical model method indicates a similar result: cerulean
warbler trend was -3.2 percent per year (95 percent C.I.: -4.2 to -2.0)
for this 40-year period (USFWS 2006, Appendix 5, slide 21 of J. Sauer's
PowerPoint presentation). This recent estimate was based on data from
243 BBS routes on which cerulean warblers were detected at least once
during that 40-year period. The rangewide relative abundance reported
from this recent analysis was 0.25 birds per route, which is relatively
low (less than 1 bird per route), and warrants some caution when
considering the BBS results for this species, because a positive bias
in the trend might occur with low counts, and because the variances are
imprecise (Sauer et al. 2005b). Within the core of the species' range
in the Appalachian Mountains (Bird Conservation Region 28), which
currently supports an estimated 80 percent of the breeding population
(as calculated using the methods described by Rosenberg and Blancher
2005), the relative abundance from the recent analysis was 1.03 birds
per route and the 40-year trend was -3.1 percent per year (95 percent
C.I.: -4.4 to -1.7; USFWS 2006, Appendix 5, slides 17-19 from J.
Sauer's presentation).
Analysis of the rangewide trend over the last 10 years (1996 to
2005) compared with the previous 30 years (1966 to 1995) indicated no
significant change in the trend between those two periods (estimated
change in trend = -0.5 percent, 95 percent confidence interval = -3.8,
+3.4). The trend estimate for cerulean warblers over the first 30 years
of the BBS was -3.0 percent per year (C.I.: -4.3, -1.8) and the
estimate for the past ten years was -3.6 percent per year (C.I.: -6.3,
-0.1). Because 10 years is a smaller sample size than 30 years, the
trend estimate based on the last 10 years is less precise than the
estimate from the previous 30 years, so that the 10-year credible
interval completely overlaps the 30-year credible interval. Thus, the
available data suggest that the trend for cerulean warblers has not
changed during the more recent period and the population continues to
decline by about 3 percent per year, including within the Appalachian
core region (Sauer 2006).
(4) Partners in Flight produced estimates of global population size
for North American land birds (Rich et al. 2004, pp. 69-77) based on a
method developed by Rosenberg and Blancher (2005, pp. 58-61). The
estimate of the cerulean warbler population was 560,000 individuals
based on an average of counts made on BBS routes during the period of
1990 to 1999; it can be thought of as an estimate for the year 1995
(the mid-point of the time period). Partners in Flight rated the
relative accuracy of their population estimates based on known sources
of variation and limitations of the methodology pertaining to each
species. Statistically derived confidence limits could not be provided
because the variance has not been measured for some of the parameters
and assumptions used in the method. Partners in Flight rated the
accuracy of the population estimate for cerulean warblers as
``moderate,'' suggesting that they felt the estimate was likely to be
within the correct order of magnitude (100,000's of birds rather than
millions or 10,000's of birds) and could be within 50 percent of the
true number (for example, 280,000 to 840,000).
The Partners in Flight method uses BBS relative abundance data
along with several assumptions and correction factors to calculate the
estimated population size for species covered by the BBS (Rosenberg and
Blancher 2005, pp. 58-61). The method is based on the idea that, at
each stop on a BBS route, an observer is recording birds within 400m
(1,300 ft ) of that stop location (per BBS survey protocol). Thus, the
observer is effectively sampling an area equal to a circle with a 400m
(1,300 ft) radius. Over the 50 stops of a BBS route, this sums to an
effective sampling area of 25.1 km\2\ (9.7 mi\2\). After making some
assumptions regarding BBS routes adequately representing habitats
across large landscapes and assumptions about the detectability of
birds, the average number of birds counted on BBS routes within a
particular region can be extrapolated across that region to calculate
an estimated population size.
The following paragraphs present a list of the primary assumptions
of the Partners in Flight method and discussion of the effects
violations of these assumptions are likely to have on calculations of
cerulean warbler population estimates.
(a) BBS routes are distributed randomly across regional strata. The
BBS methodology prescribes random distribution of survey routes within
[[Page 70722]]
sampling strata, and the assumption that BBS routes are randomly
distributed has not been questioned. However, the intensity of route
allocation within particular strata and the topographic location of
routes are two factors that could lead to biased population estimates.
For example, if BBS routes in the Appalachian Mountains tend to be
along roads that follow creek bottoms, and if cerulean warblers tend to
be more abundant on ridge tops, as indicated in Weakland and Wood
(2005, pp. 503-504), Wood et al. (2006, pp. 160-161), and Buehler et
al. (in press, p. 9), then the BBS counts could be biased by
undersampling the topographic locations where these birds are likely to
be most abundant. Both the route allocation and topographic location
biases could lead to an underestimate of total cerulean warbler
population size.
(b) BBS routes sample habitats in proportion to their relative
amounts within the regional strata. The possibility of a habitat bias
from the roadside nature of BBS routes contributes to uncertainty about
the accuracy of population estimates derived from the Partners in
Flight method. As discussed above in relation to population trend
estimation, the two studies that have been conducted in the eastern
United States have shown that BBS routes in Ohio and Maryland
undersample forest habitats compared to the surrounding landscape (Bart
et al. 1995, pp. 759-761; Keller and Scallan 1999, pp. 53-55). If a
similar bias toward underrepresenting forest habitat exists throughout
much of the cerulean warbler's range, then such a bias would result in
an underestimation of the total population size when using the Partners
in Flight method. Various efforts are underway to evaluate the habitat
bias of BBS routes across much of the United States, but results are
not available yet.
(c) Detectability of different bird species is a function of their
distance from the observer and time of day, and all species have a
fixed, average maximum detection distance. Correction factors for
detection distance and time of day were incorporated into the
estimation method to address this assumption. For the detection
distance, species were assigned to one of five categories corresponding
to different average maximum distances at which these birds were likely
to be detected based on habitat type, song quality, and likelihood of
being detected in some way other than by song (for example, hawks
soaring in the distance): 80m (260 ft), 125m (400 ft), 200m (650 ft),
400m (1,300 ft), and 800m (2,600 ft). These different detection
distances result in different effective sampling areas for BBS routes.
Cerulean warblers were assigned a detection distance of 125m (400 ft),
which is the assumed average maximum distance at which an observer will
be able to detect a singing bird. This assumption has not been tested,
and some experts believe that this detection distance might be an
overestimate of the distance at which a singing cerulean warbler can
always be heard; it is unlikely to be an under-estimate (USFWS 2006,
Appendix 4, Day 2--pp. 1-2). If the real maximum detection distance for
this species is less than 125m (400 ft), it would result in a larger
population estimate based on the Partners in Flight method. For
example, using a detection distance of 100m (325 ft) would result in a
population estimate that is approximately 60 percent higher than the
estimate using a 125m (400 ft) detection distance. The large influence
of relatively small changes in detection distance on the resulting
population estimate indicates that detection distance is a critical
parameter in the population estimation methodology and contributes a
large amount of uncertainty pertaining to the population estimate for a
particular species when the accuracy of this parameter is unknown.
To correct for detection issues associated with time of day,
Rosenberg and Blancher (2005, pp. 59-61) developed distribution curves
of the detections for each species over the 50 stops of BBS routes.
Based on these curves, peak detection probabilities were determined for
each species and then a ratio of the peak detections to average
detections was calculated. This ratio is used to adjust the average
numbers of birds detected per route to peak numbers per route,
reflecting numbers that would be expected if the peak detection
probability lasted throughout the morning hours when BBS routes are
surveyed. The time of day correction factor calculated for cerulean
warbler is 1.35 (Rosenberg and Blancher 2005, p. 63--Table 2). The
methods for deriving this correction factor are empirically based, and
there is little reason to believe that it is biased or otherwise
inappropriate for cerulean warblers.
One potential correction factor that was not incorporated into the
Rosenberg and Blancher (2005) method and that could influence
population estimates for cerulean warblers is a correction for
detectability associated with the season. The song rate of most
cerulean warbler males declines once they become mated and as the
breeding season progresses (USFWS 2006, Appendix 4, Day 2--p. 2). The
breeding season typically begins between mid-April and early May
throughout much of the breeding range. Most BBS routes are run during
the first half of June, and overall song rate of mated males is likely
to be lower at that time than earlier in the breeding season. Such a
time of season effect could contribute to an under-estimate of the
total cerulean warbler population size.
(d) Individuals detected during a count represent one member of a
pair. A pair correction factor of two times the initial estimate was
also incorporated into the method to address Assumption D. Most
individuals in breeding populations are mated during the time of the
BBS survey, but it is usually only one member of each pair that is
detected (for example, a singing male). Rosenberg and Blancher (2005,
p. 61) acknowledge that the appropriate pair correction factor for all
species is somewhere between one and two, because not all individuals
in a breeding population are mated. However, this correction factor has
not been empirically established for any species yet. Field studies
indicate that not all male cerulean warblers attract mates during the
breeding season, although some males of this species are also known to
be bigamous (USFWS 2006, Appendix 4, Day 2--p. 2). The proportion of
unmated and bigamous males across the species range is unknown. The
most appropriate pair correction factor for cerulean warblers might be
a number less than two, but insufficient data currently exist to
estimate what this number should be for the entire population. A pair
correction factor less than two would result in a smaller population
estimate, while a pair correction factor greater than two would result
in a larger population estimate.
Status of the Cerulean Warbler Population
We used a stepwise approach to evaluate what single factor or
combination of factors may affect the cerulean warbler's population
trend in order to evaluate whether the species warrants listing as
threatened or endangered under the Endangered Species Act. First, we
used all available information, including that contained within the
petition, scientific literature, and expert opinion (USFWS 2006) to
identify potential factors that might explain the historical and
projected population trends (see previous section ``Population Size and
Trend''). Next, we gathered information to assess whether the
likelihood of occurrence or magnitude of effect of the factors were
likely to result in population-level effects. We used the qualitative
judgments of independent experts (USFWS 2006) to assess these potential
[[Page 70723]]
causal factors where quantitative data are unavailable. Then, we
synthesized the information on the past and future factors with
estimates of historical (Link and Sauer 2002, p. 2837, Sauer 2006) and
projected (Thogmartin 2006) cerulean warbler population trends to
estimate to what degree potential factors might influence the species'
risk of extinction. Finally, we compared the results of our analysis to
the five factors listed in the Act to ensure thorough consideration of
potential threats, and, in light of the Act's five-factor analysis, we
evaluated whether the species' current or projected status met the
definitions of threatened and endangered.
Summary of Factors Affecting the Species
Section 4 of the Act (16 U.S.C. 1533) and our implementing
regulations at 50 CFR part 424 set forth the procedures for adding
species to the Federal endangered and threatened species list. A
species may be determined to be an endangered or threatened species due
to one or more of the five factors described in section 4(a)(1), as
follows: (A) The present or threatened destruction, modification, or
curtailment of its habitat or range; (B) overutilization for
commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) the inadequacy of existing regulatory
mechanisms; or (E) other natural or manmade factors affecting its
continued existence. In making this finding, information regarding the
status of, and threats to, the cerulean warbler in relation to the five
factors is discussed below.
In developing our 12-month finding for the cerulean warbler, we
considered all scientific and commercial information on the status of
the species that we received during the comment period following our
90-day finding. We also searched the scientific literature for relevant
data and consulted experts on the cerulean warbler and threats to its
habitat to ensure that this finding is based on the best scientific and
commercial data available.
As noted earlier, we considered the population trend estimate of -
3.2 percent per year (CI = -4.2 to -2.0), which is based on Breeding
Bird Survey data (Link and Sauer 2002, p. 2837; Sauer unpublished data
2006), to be the best available representation of the species
population status. This trend estimate comprises all of the factors
causing population change during the 40-year period of Breeding Bird
Survey data collection. In other words, all the factors affecting
cerulean warbler demographics have combined over the past 40 years to
produce an annual average decline of 3.2 percent per year, with 90
percent certainty that the true decline is between 4.2 and 2.0 percent
per year (Link and Sauer 2002, p. 2837; Sauer unpublished data 2006).
The information available suggests that the factors described in this
section will continue affecting cerulean warbler habitats and
demography in a similar manner, resulting in a continuing population
decline of approximately 2 to 4 percent per year.
We describe the potential contributing factors to the species'
approximately 3 percent annual decline in the following description of
the five listing factors (iterated above).
A. The Present or Threatened Destruction, Modification, or Curtailment
of Its Habitat or Range
After consideration of all available information, the Service has
determined that four biological mechanisms operating throughout the
species' annual range are likely to be primary contributors to the
species' declining population trend. Each of these mechanisms is
related to changes in habitat in North America, South America, and
along the species' migration routes. These mechanisms are:
1. Reduction in available nesting sites and suitable breeding
territory characteristics because of loss or degradation of habitat,
2. Reduction in foraging success resulting from decreased prey
abundance, primarily on the wintering ground in South America,
3. Increased predation throughout the species' annual range and
nest parasitism of cerulean warblers in the breeding grounds, resulting
from habitat fragmentation, and
4. Loss of migration habitat.
Each of these four mechanisms results, either directly or
indirectly, from the reductions in quality and quantity of cerulean
warbler habitat (Factor A of the Act) and therefore, all will be
discussed under Factor A.
1. Reduction in available nesting sites and suitable breeding
territory characteristics because of loss or degradation of habitat:
Although we do not have a rangewide numerical relationship between
habitat loss and population change, we do know that there is a positive
relationship between cerulean warbler nest presence and mature and old-
growth hardwood forests with large trees, small gaps, and vertical
diversity in vegetation layers (Hamel 2000b, pp. 12-18; Weakland and
Wood 2002, p. 13). Therefore, we can conclude that degradation or
removal of suitable mature and old-growth hardwood forestland will
result in reductions in nesting opportunities, and that accumulation of
habitat losses is likely to result in declines in cerulean warblers.
We do not know what happens to individual birds when breeding
habitat is removed. Displacement of adults and mortality of nestlings
is likely if removal of nesting stands occurs during the breeding
season. Nestling or post-fledging mortality may also occur if habitat
within nesting territories is eliminated or quality is reduced below an
unknown threshold level. Results of recent studies suggest that
cerulean warblers are capable of interannual movement (Veit et al.
2005, pp. 165-166; USFWS 2006, Appendix 5f, slide 17 of Jones
PowerPoint); therefore, breeding habitat loss during the non-breeding
season is likely to result in relocation of adults that return during
the subsequent breeding season. However, the degree to which
reproductive success or survival of displaced individuals is affected
is likely dependent upon several variables, including whether the
displaced birds relocate into already occupied or unoccupied, or
whether remaining habitat is optimal or suboptimal. We do not have
information to assess the degree and type of impact of breeding habitat
of site-specific habitat loss, unless known occupied nests are removed.
Degradation of habitat quality can occur at several scales, and the
resulting effect on cerulean warblers is likely to be context-
dependent. Loss of a single dominant tree in a stand possessing
numerous other dominant trees may have little or no effect on the
reproductive success of breeding cerulean warblers, whereas loss of a
single dominant tree in a stand having few other large trees may render
a formerly suitable site unsuitable for nesting birds. Context is
probably similarly important at larger scales. Reduction in patch size
and introduction of hard edges may result in greater local population
declines and habitat unsuitability where a forest stand is surrounded
by an already fragmented landscape as opposed to largely intact forest.
Thus, habitat content factors that operate at local scales (to include
nest trees, prey base, etc.) and habitat context factors that operate
at larger scales (to include things like habitat patch size, degree of
landscape fragmentation, etc.) are both important determinants of
overall habitat quality for breeding cerulean warblers.
[[Page 70724]]
The amount, distribution, and quality of habitat for breeding
cerulean warblers has been altered dramatically since European
settlement in the early 1600s. An estimate of total forestland in 1630
in 19 States in which cerulean warblers occur today and for which there
was analyzed BBS data (Sauer 2006) was 133,000,000 ha (328,695,000 ac)
(Smith et al. 2004, p. 33, citing Kellogg 1909). Today, the estimate of
forest cover in those same States is 73,600,000 ha (181,850,000 ac)
(Smith et al. 2004, p. 33), a total reduction of approximately 45
percent. The most dramatic change occurred between the early 1600s and
1900, when approximately 51 percent of forestland was converted to
agricultural and other uses (Smith et al. 2004, p. 33). Since 1900,
approximately 8,500,000 ha (21,000,000 ac) have reverted from primarily
agricultural uses to forestland. Approximately 52 percent of today's
hardwood forest within the eastern United States is in mature sawtimber
(Smith et al. 2004, p. 64); some of this area is northern hardwood
forest and outside the range of the cerulean warbler.
The cerulean warbler appears capable of using previously unoccupied
stands that have matured to develop necessary habitat characteristics.
Evidence of this capacity comes from New Jersey, New York, and parts of
New England, where the species has recently expanded its range (Hamel
1992, pp. 385-400; Robbins et al. 1992, p. 551). Population information
indicates that this expansion occurred during the later part of the
1900s, although experts suggest that the expansion does not appear to
be continuing today (USFWS 2006, Appendix 4, Part II, p. 5). We do not
know the distribution of cerulean warblers prior to 1966; therefore, we
do not know whether this expansion is a reoccupation of restored forest
or true expansion into an area not previously occupied.
Despite this recent, gradual increase in the total amount of
forestland, cerulean warbler populations have declined since 1966,
according to Breeding Bird Survey data. Several hypotheses could
explain this phenomenon: (1) The amount of forest stands with diverse
structure continues to decline even though total forestland acres
increases; (2) local reductions in nesting opportunities in core
breeding areas are having disproportionate effects at the population
level; or (3) factors occurring elsewhere in the species annual range
or not related to nesting opportunities are causing the decline. We
will discuss each of the first two of these factors in the following
text, and the third factor in subsequent sections.
Rangewide data are not available to quantitatively assess the
amount of or change in habitat with desired characteristics for
breeding birds. Nevertheless, several pieces of information are
important for consideration. It takes hundreds of years for hardwood
forests to naturally achieve complex structure of mature and old-growth
forests (Hamel 2000, p. 12 citing Widman), which are characteristic of
stands selected by cerulean warblers for breeding. Much of the
reversion of agricultural lands to forestland has occurred since the
early 1900s; therefore, much of the new acreage in forestland remains
in relatively younger stands that have yet to achieve desired
structural complexity. We note, however, that stand heterogeneity is
likely a more important predictor of habitat quality than simply
looking at stand age, because natural and anthropogenic disturbances
can create desired stand complexity. Forest management practices, such
as high-grading, may also affect habitat quality if the largest trees
in the stand are removed, reducing structural complexity. Fire
suppression, species-specific tree diseases, and locally or regionally
high deer densities may also reduce the complexity of forest structure.
Effects in a relatively small portion of the species' range,
compared to the species' entire breeding range, could contribute
disproportionately to the population decline. This has likely happened
in the past and may happen in the future. Historically, cerulean
warblers were probably numerous in the bottomland hardwood forests of
the Mississippi Alluvial Valley. Today, approximately 80 percent of
forest in this area has been converted to nonforest uses (Brown et al.
2000, p. 6). Nesting cerulean warblers currently occur only in
scattered locations within this region. It is important to note that
most of this loss occurred before the Breeding Bird Survey began in
1966. Currently, large-scale habitat loss is occurring in the core of
the species' range, Kentucky and West Virginia, where mountaintop coal
mining and valley fill operations through 2012 are expected to remove
567,000 ha (1.4 million ac) of suitable forest habitat (USEPA 2005).
The total cumulative forest loss from these activities will likely
eliminate breeding habitat for 10 to 20 percent of the total cerulean
warbler population currently occurring within that core area. The loss
of breeding opportunities for birds in this area may have a
disproportionate effect on the species' total population size.
The USDA Forest Service has projected forest change to the year
2050 (Alig and Butler 2004). These projections are based on prior
trends in forest change, expected market conditions, and no change in
forest management related policies. Under these conditions, the Forest
Service expects a slight decline in hardwood forest area. Hardwoods
will continue to dominate the southeastern United States; however
hardwood forest area is expected to decline by up to 18 percent by 2050
(Alig and Butler 2004, pp. 32-33). Maple-beech-birch and oak-hickory
forests are estimated to decrease by 6 percent and 15 percent,
respectively (Alig and Butler 2004 p. 18). We note that small portions
of the hardwood forest area contained within these estimates are
outside the range of the cerulean warbler; refer to Alig and Butler
(2004, p. 2) for a map of the forest survey area. We stress that
changes in acreage or percent of forest landscape in hardwoods are only
one determinant, and the actual composition and structure of hardwoods
forests in future landscapes may be equally or more important.
In summary, a variety of factors has affected the quantity and
quality of mature and old-growth hardwood forests within the range of
the cerulean warbler. Overall, habitat loss beginning in the 1600s
likely precipitated a decline in cerulean warblers; however, the
conversion of forests stabilized with about 50 percent of forestland
remaining in the early 1900s. Rangewide cerulean warbler population
information did not become available until the 1960s; therefore, we do
not know how the pre-1900s cerulean warbler population size changed as
a result of this dramatic habitat loss, nor how it may have responded
to post-1900 forest changes. Beginning in the 1900s, re-growth of
forests previously converted to agriculture has added potential
breeding habitat that may be reoccupied when stands achieve the
characteristics selected for by cerulean warblers, as evidenced today
in the Northeastern United States.
2. Reduction in foraging success resulting from decreased prey
abundance, primarily on the wintering ground in South America:
Cerulean warblers feed exclusively on insects in North America, and
on insects and nectar in South America. Availability of these resources
is critical to an individual bird's survival. Insufficient fat storage
before spring migration could increase an individual's risk of
mortality and decrease reproductive success upon return to the breeding
grounds. Insufficient fat
[[Page 70725]]
storage before fall migration could leave an individual at risk of
mortality, especially if the migration route is over water where
foraging opportunities are limited, as is currently hypothesized.
Winter range--Abundance of food resources in South America has
likely declined because of the degradation and removal of tropical
forests. Removal of overstory trees, as forests are cleared and shade-
grown coffee plantations are converted to sun coffee plantations, is
expected to result in losses of arthropods that are specialized for the
canopy layers. For example, in Costa Rica, Perfecto (1996, p. 602)
reported an average of 72 percent of the ants in a tropical forest tree
canopy to be canopy specialists. However, that we do not know that
cerulean warblers prey on ants. In a Costa Rican study, Perfecto et al.
(1996, p. 602) reported similar arthropod diversity in overstory trees
within shade-grown coffee plantations as within a native forest canopy.
We do not have figures for arthropod diversity or abundance in the
Northern Andes, but we expect that conditions may be similar. We do not
have quantitative information on the differences in nectar resources
between tropical forest and developed lands.
Moreno et al. (2006, p. 3) used a climatic and geospatial model to
predict the potential maximum occurrence of cerulean warbler wintering
habitat in the narrow elevation zone (500 to 1,500 m (1,650 to 5,000
ft)) in the Northern Andes and estimated a nearly 60 percent current
reduction from maximum levels. The remaining habitat is tropical forest
and shade-coffee plantations. Some field biologists believe that the
model overestimates habitat availability, and they estimate that less
than 10 percent remains (Moreno et al. 2006 unpublished report, pp. 3,
5).
Most of the loss of tropical forests in the Northern Andes occurred
within the latter half of the 1900s. Approximately 15 percent of the
species' modeled potential habitat (Moreno et al. 2006 unpublished
report, p. 5) is managed under protective status. The effectiveness of
this protective status for conserving cerulean warblers is uncertain
because none of the documented cerulean warbler winter occurrences are
within protected areas (Moreno et al. 2006 unpublished report, p. 5).
The rate of loss of the remaining tropical forest is likely to be
decreasing because remnant forests are in steep and inaccessible areas;
however, removal of portions of the remaining tropical forests
continues.
We know that cerulean warblers occupy shade-coffee plantations
during the non-breeding season, but we do not know whether shade-coffee
plantations are optimal or sub-optimal habitat because data are not
available to compare body condition of cerulean warbler on shade-coffee
plantations with birds occupying tropical forests. In other words,
presence does not necessarily equate to suitability of these habitats.
The amount of habitat supplied by shade-coffee plantations is
diminishing, as some of these plantations are converted to sun-coffee
plantations that lack the overstory required by wintering cerulean
warblers (Moreno et al. 2006 unpublished report, p. 2). Cerulean
warblers are not known, and are highly unlikely, to occur in sun-coffee
plantations due to the plainly inadequate structure of such vegetation.
In summary, the population-level effects of habitat loss and
degradation on forage abundance and foraging success have not been
quantified. It is reasonable to conclude, however, that a greater than
60 percent decline of wintering habitat in South America has
contributed to the approximately 3 percent annual population decline of
cerulean warblers through reduced forage availability and increased
competition for remaining food resources.
Breeding and Post-Fledging Range--Under pre-European settlement
conditions on the breeding grounds, the hardwood forests of the eastern
United States were a mosaic of different seral stages (Williams 1989,
pp. 22-49). Although the forests were predominately mature and old
growth, patches of younger seral-stage forests occurred within small
gaps (Lorimer 1989, pp. 565-566). Today, cerulean warblers occur in
greater relative abundance within landscapes with similar mosaic
characteristics. Information suggests that cerulean warblers select
nests sites in stands where canopies are interrupted by small gaps and
canopy closure is between 65 percent and 85 percent (Hamel 2000, p.
16). Nests are found in areas with large diameter trees and stands with
complex canopies, but small patches of seedling-sapling aged trees
within the mature forest mosaic may provide important habitat for post-
fledging first-year birds.
Today's mature forest characteristics may not mimic the mosaic
conditions of original hardwood forest because of alterations in the
disturbance regimes through fire suppression, dense populations of
deer, and certain timber harvest methods. The effects of this change in
forest disturbance regimes on cerulean warblers are not well studied or
understood. It is possible, however, that the replacement of the
natural disturbance regime--characterized by frequent, small-scale
disturbances--with the less-frequent larger-scale disturbances (Lorimer
1989, pp. 565-566) may not produce understory conditions that favor
foraging success for post-fledging birds because of the lack of
interspersed seedling-sapling patches.
3. Increased predation throughout the species' annual range and
nest parasitism of cerulean warblers in the breeding grounds, resulting
from habitat fragmentation:
Fragmentation of cerulean warbler habitat has occurred throughout
the species' range. High rates of predation and brood parasitism often
accompany habitat loss and fragmentation, especially in forested
landscapes interspersed with agricultural lands and grasslands (Hoover
and Brittingham 1993, p. 234; Brittingham and Temple 1983, pp. 31-34;
Faaborg et al. in Martin and Finch 1995, p. 361). Several studies have
shown low rates of nest success (less than 40 percent) for cerulean
warblers in areas of fragmented forest within agricultural landscapes
due to high levels of predation and the presence of nest parasitism
(Hamel 2000a, p. 4; Roth 2004, p. 43; Varble 2006 p. 3). Direct
measurements of adult and post fledging mortality due to habitat loss
and fragmentation during the breeding season on cerulean warblers do
not exist; however, this phenomenon is well documented with other
canopy and sub-canopy nesting songbird species. It is reasonable to
conclude that brood parasitism and predation are exacerbated by habitat
loss and fragmentation and that this is contributing to the
approximately 3 percent annual population decline.
Wintering Range--Effects of habitat loss and fragmentation include
increased risk of mortality from predation of neotropical migrant
songbirds in the non-breeding range (Rappole et al. 1989, p. 407; Petit
et al. in Martin and Finch 1995, pp. 179-180), especially if birds are
forced to wander outside optimal habitat. Although no studies of
predation on cerulean warblers in the non-breeding range have been
conducted, it is reasonable to assume that predation-caused mortality
of cerulean warblers is similar to that documented for other warbler
species.
Approximately 60 to 90 percent of wintering habitat of cerulean
warblers in South America has been converted to other land uses. This
loss of habitat has resulted in a highly fragmented landscape.
Geospatial modeling estimates that fragmentation of this habitat has
more than doubled (Moreno et al. 2006, p. 14, unpublished report).
[[Page 70726]]
Breeding Range--Nest parasitism and predation usually result in
mortality of nestlings and post-fledging birds. Brown-headed cowbirds
(Molothrus ater) lay their eggs in the nests of other species, and when
hatched, cowbird chicks outcompete the chicks of the natural parents.
Likely nest predators are corvids, chipmunks, squirrels, and other
arboreal animals.
Populations of cowbirds and avian predators are higher in highly
fragmented forests and in areas where edges delineate sharp differences
in land use between the forests and the adjacent stands. For example,
cowbird abundance is greater along forest and agricultural edges than
along edges created by different forest age classes (Rodewald and
Yahner 2001, p. 1021) and are more common where human development
provides new feeding sites, such as pastures. Overall, however, cowbird
populations have declined since breeding bird surveys began in 1966
(Robbins et al. 1992, p. 7661). We do not know whether, or the degree
to which, reductions in cowbird populations result in less pressure on
cerulean warblers.
Effects of habitat loss and fragmentation on songbirds of North
America have been relatively well studied compared with birds in South
America; however, little specific information is available on cerulean
warblers. In general, we know that increased fragmentation and
decreased habitat patch size within the breeding range is likely to
increase risk of predation and nest parasitism (Robinson et al. 1995,
pp. 1988-1989; Donovan et al. 1995, p. 1393). Nest success was low
(less than 25 percent) at Big Oaks National Wildlife Refuge in Indiana
due to nest predation and nest parasitism; the breeding habitat on the
refuge is surrounded by an agriculturally dominated landscape (Roth
2004, p. 43; Varble 2006, p. 3).
Studies on cerulean warblers have concluded that increased distance
from edge was a significant positive predictor of cerulean warbler
territory density (Bosworth 2003, p. 21; Weakland and Wood 2002, p.
505). The reason for decreased cerulean warbler density near edges is
not known, but may be a result of lower availability of suitable or
optimal habitat near edges, or edge habitat avoidance, possibly as a
result of increased predation pressure or other factors. The effects of
fragmentation are likely to be context-dependent, where increasingly
fragmented landscapes lead to decreased reproductive success due to
increased predation and brood parasitism (Donovan et al. 1995, p.
1393). Specifically, Donovan et al. (1995) found that nest failures of
three forest-nesting, neotropical migrants (ovenbird (Seiurus
aurocapillus), red-eyed vireo (Vireo olivaceus), and wood thrush
(Hylocichla mustelina)), were significantly higher in fragmented
forests than in contiguous forests.
4. Loss of migration habitat:
Migrating warblers that cross the Gulf of Mexico to and from
breeding and wintering grounds depend on finding suitable patches of
terrestrial habitat near coastlines. Such habitats are essential in
providing food resources necessary to replenish energy and fat stores
of enroute migrants and to provide shelter from predation and inclement
weather events. As coastal forest habitat along the U.S. and Central
American Gulf coasts is lost to development and conversion, compounding
the adverse impacts of hurricanes and other natural factors, the
vulnerability of cerulean warblers to mortality during migration has
increased.
Conservation Actions Currently Underway
There are several existing conservation actions and programs that
specifically focus on the cerulean warbler and its habitat. We did not
rely on these ongoing conservation actions in our determination that
listing the cerulean warbler is not warranted and, therefore, we did
not evaluate them under our 2003 Policy for Evaluation of Conservation
Efforts When Making Listing Decisions (68 FR 15100; March 28, 2003).
The cerulean warbler Technical Group (CWTG) is a partnership of
biologists, managers, and scientists from the forest-products industry,
Federal and State agencies, nongovernmental organizations, and
academia. It was formed in 2001 to develop a broad-based, technically
sound approach to conservation of the cerulean warbler. By seizing the
initiative and bringing key stakeholders and technical experts
together, the CWTG seeks to keep the focus on identifying meaningful
and proactive conservation solutions through sound science, clear
communication, and trust. CWTG was loosely modeled after the highly
successful Louisiana Black Bear Conservation Committee formed in the
early 1990s. Collaborative actions of the CWTG on behalf of the species
are coordinated by a Steering Committee charged to spur action and
chart future activities and directions. There are currently 72 CWTG
participants working on the following committees: Coordination,
conservation, monitoring, research, international, and mining. Hamel et
al. (2004, pp. 12-14) provides a thorough discussion on the history,
organization, and objectives of the CWTG.
In December 2002, the CWTG met at the National Conservation
Training Center in Shepherdstown, West Virginia, at a workshop
sponsored by the Service and the U.S. Geological Survey. This important
workshop was attended by 65 people from a broad category of
disciplines, including biologists from Colombia, Ecuador, and
Venezuela. The main purpose of the workshop was to develop a proactive,
broad-based, and cohesive strategy for cerulean warbler conservation.
Four working groups were established; their goals and accomplishments
are summarized below:
(1) The Breeding Season Research Group identified rangewide
research priorities and designed a research experiment to test cerulean
warbler response to commonly applied forest management practices,
replicated at five study areas across the core of the breeding range.
The project will provide information on cerulean warbler ecology and
demography, and insights to key limiting factors and to management
prescriptions that could benefit it and associated species. In 2003,
the project was endorsed by the Northeast and Southeast working groups
of Partners in Flight as the highest research priority for forest
songbird conservation.
(2) Priorities for the Breeding Season Surveys and Monitoring Group
are to map cerulean warbler distribution more completely, improve
regional and global estimates of population size and trend, and
integrate inventory and monitoring efforts with predictive modeling.
Successes include bringing together major forest-products companies in
the mid-Appalachians in partnership with the National Council for Air
and Stream Improvement (NCASI) and the Cornell Laboratory of
Ornithology to evaluate cerulean warbler status on as much as 100,000
ha (250,000 ac) of likely suitable habitat that have not previously
been surveyed. During the nesting seasons of 2003 to 2005, the partners
surveyed hundreds of points on private lands. The data are being used
to test and refine predictive models, developed by University of
Tennessee, the Service, and U.S. Geological Survey, on the spatial
distribution, abundance, and habitat associations of cerulean warblers
in their core breeding range.
(3) The Breeding Season Conservation Group is developing a vision
and goals for long-term sustainability of cerulean warblers within the
context of integrated ecosystem conservation and to develop habitat
conservation and management recommendations for the
[[Page 70727]]
cerulean warbler that can be incorporated into management plans for
public and private forestlands within its range. One venue for pursuing
these goals is the Appalachian Mountains Bird Conservation Initiative
(under the Atlantic Coast Joint Venture), a partnership organized to
facilitate effective proactive conservation for all birds in the
Appalachian Mountains region with an emphasis on cerulean warblers and
ecologically related species.
(4) The Non-Breeding Season Group, El Grupo Cer[uacute]leo,
promotes a multispecies approach to habitat conservation on the
wintering grounds (including other resident at-risk species that co-
occur with cerulean warblers). This group has compiled a database of
documented observations of cerulean warblers, assessed non-breeding
threats and conservation coverage, identified opportunities for
outreach and education to communicate awareness of migratory bird
issues, and (through the U.S.D.A. Forest Service and The Nature
Conservancy) provided funding for South American biologists to conduct
new research on cerulean warblers in the winters of 2003-2004 through
2005-2006. Two workshops (March 2003 and November 2005) in Ecuador with
biologists and modelers from throughout northern South America resulted
in GIS-based, spatially explicit models of cerulean warbler winter
habitat. El Grupo Cer[uacute]leo recently assisted other conservation
organizations in securing an important non-breeding habitat reserve for
the cerulean warbler in Colombia (see more on this action in discussion
of Important Bird Areas below).
The cerulean warbler Technical Group is moving forward on the
premise that the most successful conservation efforts for cerulean
warblers will be those that bring together broad partnerships to
achieve common goals. To that end, the CWTG Steering Committee
conducted two separate one-day meetings with forest and coal industry
biologists and managers in March 2006 in Charlestown, West Virginia.
The purpose of these meetings was to begin discussions with these two
industries on cooperative efforts to broaden cerulean warbler
conservation management. Both meetings explored the constraints and
potential options for cerulean warbler conservation in the Appalachians
and establishing a foundation for a broader conservation partnership
summit in February of 2007 that will focus on actions.
There are several projects currently being conducted to study the
response of cerulean warblers to targeted management efforts to restore
the quantity and quality of its breeding habitat. As previously
discussed in this finding, quality cerulean warbler breeding habitat
consists of mature forests with a diverse and vertically complex canopy
structure, including canopy gaps and associated midstory and understory
vegetation. Biologists and land managers are manipulating (managing)
forest areas to create the complex canopy structure required by
cerulean warblers. If these research and management studies are
successful, these methods could be used in many public and private
forests to restore the cerulean warbler's breeding habitat and enhance
its reproductive capability in a shorter period of time.
The most comprehensive effort involving the scientific evaluation
of managing and restoring cerulean warbler breeding habitat is the
Cooperative Cerulean Warbler Forest Management Project, which was
developed by the Cerulean Warbler Technical Group. Study areas include
a national forest in eastern Kentucky, a State wildlife area in north-
central Tennessee, a State wildlife area in southeastern Ohio, a State
wildlife area in north-central West Virginia, national forests in
eastern West Virginia, and an area of private forest industry lands in
the coal fields of southern West Virginia. Each study area will consist
of four sites representing different levels of forest management
intensity: (1) No management, (2) selective harvest with 75 percent
residual canopy cover, (3) selective harvest with 50 percent residual
canopy cover, and (4) even-aged harvest (clearcutting, less than 10
percent residual canopy cover). Each site will be 20 ha (50 ac), with
the management actions being applied on a 10 ha (25 ac) area in the
center of each site. This configuration will allow for an undisturbed
buffer at least 100 m (330 ft) to isolate the management activities and
for assessing edge effects around the different levels of management
intensity. Two years of pre-harvest monitoring (2005, 2006) and two
years of post-harvest monitoring (2007, 2008) will occur on each site.
The pre-harvest monitoring has been conducted and the forest management
actions are scheduled to occur during the fall and winter of 2006-2007.
A similar forest management-cerulean warbler study is being conducted
on the Chattahoochee National Forest in northern Georgia.
In 2005, Fundacion Aves (the ProAves Foundation of Colombia) and
the American Bird Conservancy were successful in securing a 1,250-ha
(500-acre) reserve of Andean subtropical forest in the Rio Chucur basin
of Santander, Colombia (within the Serrania de los Yariguies Important
Bird Area) to protect wintering habitat for the cerulean warbler. The
area, one of the last natural forest fragments in the region, contains
high populations of wintering cerulean warblers. This is the first
South American reserve designed to protect a bird species that nests
solely in the United States and Canada. The reserve is also a focal
point for a continuing regional conservation campaign for the cerulean
warbler. Another key area for wintering cerulean warblers--southwestern
Antioquia, Colombia--has been targeted for further conservation
efforts.
Factor A Summary
We believe that the combined effects of habitat loss have
accumulated to produce the 40-year average annual decline of 3.2
percent per year, with 90 percent certainty that the true decline is
between 4.2 and 2.0 percent per year. As stated earlier, we do not have
information to suggest that the population trend will shift outside the
credible interval (Link and Sauer 2002, p. 2837; Sauer 2006) in the
future, and we, therefore, assume that the factors described above will
continue to support the declining population trend between -4.2 and -
2.0 per year. Notwithstanding this assumption, the Service does not
find that the cerulean warbler is likely to become a threatened or
endangered species within the foreseeable future throughout all or a
significant portion of its range.
B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
We are not aware of any commercial, recreational, or educational
uses that result in adverse impacts to the species or to individuals,
nor do we envision any such threats developing in the foreseeable
future.
There is a potential for adverse impacts resulting from scientific
purposes, but data indicate that such impacts are negligible. All
scientific activities in the United States that involve taking (for
example, pursuing, capturing, hunting, shooting, wounding) cerulean
warblers, their nests, or their eggs require a permit issued by the
Service under authority of the Migratory Bird Treaty Act. In the United
States, 13 cerulean warblers were taken under scientific research
permits from the beginning of 2000 to the present, an average of fewer
than 3 birds per year. Currently there are four valid and active
scientific collection permits that allow the potential lethal take of
up to 20 additional cerulean warblers through
[[Page 70728]]
March 31, 2008 (Andrea Kirk, Migratory Birds Permit Chief, USFWS Region
3, 2006, in litt.). This level of mortality is deemed to be of
negligible impact on a species whose population is most likely in the
hundreds of thousands of individuals.
Other research projects that include handling cerulean warblers,
such as capturing and handling individuals for banding or applying
other markings, may accidentally result in serious injury or death to a
small percentage of the captured birds. Permits for these activities
are issued by the Bird Banding Laboratory (BBL) of the Biological
Resources Division of the U.S. Geological Survey. Data from the BBL
show that only 1,879 cerulean warblers were banded during the 50-year
period from 1955 to 2004 (BBL data, accessed on September 8, 2006, at
http://www.pwrc.usgs.gov/BBL/homepage/listalph.htm). The number of
cerulean warblers banded during this period is much lower than almost
all other warbler species banded during this 50-year period (only four
other warbler species had a lower number of bandings). For instance,
3,469 golden-cheeked warblers and 3,236 Kirtland's warblers (both
endangered) were banded during this period and 26,919 blackburnian
warblers. Compared to banding activities involving other warbler
species, this is a very low incidence of banding and handling,
indicates that there has been little intentional or incidental banding
activity with this species. The behavior of cerulean warblers generally
keeps them high in the forest canopy, leading to a low frequency of
capture in the mist nets used by bird banders. Thus, we conclude that
there are few (if any) adverse populations impacts resulting from
banding or marking this species.
We have no data concerning the impacts of scientific research on
this species along its migratory route or on its wintering grounds, but
there is no reason to suspect those activities have or will produce
significant adverse impacts on the species.
In summary, the best available scientific data indicate that there
are no significant impacts occurring to the species from
overutilization for commercial, recreational, scientific, or
educational purposes.
C. Disease or Predation
We found no evidence to suggest that avian diseases or parasites
are affecting cerulean warblers beyond normal baseline levels.
The possible increased impacts of predation and nest parasitism are
believed to be caused by changes in habitat quality. Therefore, these
impacts are discussed under Factor A, above.
D. The Inadequacy of Existing Regulatory Mechanisms
Existing regulatory mechanisms that could provide some protection
for the cerulean warbler include: (1) United States Federal laws,
regulations, and Executive Orders; (2) Canadian Federal and Provincial
Laws and Regulations; and (3) State wildlife laws, which are discussed
below.
(1) U.S. Federal Laws, Regulations, and Executive Orders
The Migratory Bird Treaty Act (MBTA; 16 U.S.C. 703-712) prohibits
``take'' of any migratory bird. ``Take'' is defined as to pursue, hunt,
shoot, wound, kill, trap, capture, or collect, or attempt to pursue,
hunt, shoot, wound, kill, trap, capture, or collect.
The National Environmental Policy Act (NEPA; 42 U.S.C. 4321 et
seq.) requires all Federal agencies to formally document, consider, and
publicly disclose the environmental impacts of their actions and
management decisions. NEPA documentation of these impacts is provided
in an environmental impact statement, an environmental assessment, or a
categorical exclusion, and may be subject to administrative or judicial
appeal. In NEPA documents, Federal agencies may present scientific
studies, evaluations, and management decisions involving actions that
may impact the cerulean warbler or its habitat. Some Federal agencies
may be required by their regulations, policies, and guidance to perform
specific assessments under NEPA for actions that could impact the
cerulean warbler. Examples include biological evaluations addressing
actions by the U.S. Forest Service on national forests where the
cerulean warbler is identified as a sensitive species by the Regional
Forester.
The Multiple-Use Sustained-Yield Act of 1960, as amended (MUSY; 16
U.S.C. 528-531) provides direction that the national forests be managed
using principles of multiple uses and to produce a sustained yield of
products and services. Specifically, MUSY provides policy that the
national forests are established and shall be administered for outdoor
recreation, range, timber, watershed, and wildlife and fish purposes.
Land management for multiple uses necessarily raises competing and
conflicting issues. MUSY provides direction to the Forest Service that
wildlife, including the cerulean warbler, is a value that must be
managed for, though discretion is given to each forest when considering
the value of this species relative to the other uses for which it is
managing. Although MUSY could provide some protection for the warbler,
it does not have any provisions specific to the conservation of the
warbler or its habitat.
The National Forest Management Act (NFMA) as amended (16 U.S.C.
1600-1614) is the primary law governing the administration of national
forests by the U.S. Forest Service. NMFA requires all units of the
National Forest System to have a Resource Management Plan (RMP), to
revise the plans whenever significant changes occur in a unit, and to
update the plans at least once every 15 years. The purpose of the RMP
is to guide and set standards for all natural resource management
activities over time. NFMA requires the Forest Service to incorporate
standards and guidelines into RMPs, including provisions to support and
manage plant and animal communities for diversity, and the long-term
rangewide viability of native and desired nonnative species. Several
national forests have identified the cerulean warbler as a ``sensitive
species,'' which involves an additional assessment of the impact of
individual management actions by the national forest on the cerulean
warbler. National forests that have identified the cerulean warbler as
a sensitive species have current information on the presence and
condition of the warbler and its habitat on the national forests and
within individual units where management actions are planned. Surveys
for cerulean warblers may be conducted prior to undertaking management
actions or to monitor population trends of cerulean warblers, including
national forests where the species is not designated as a sensitive
species. The cerulean warbler has also been identified as a Management
Indicator Species on several national forests. In these cases, the
cerulean warbler functions as a biological indicator of desired forest
condition, and results in a higher level of awareness of the species'
life history and habitat needs, which are considered during analysis of
the impacts of site-specific management activities by the national
forest. The NFMA allows for habitat management specifically to benefit
cerulean warblers on national forests within the species' historical
range.
The Surface Mining Control and Reclamation Act (SMCRA; 25 U.S.C.
1201) addresses the necessary approvals for surface mining operations,
as well as inspection and enforcement of mine sites until reclamation
responsibilities are completed and all performance bonds are released.
This law, which regulates the recovery of coal by
[[Page 70729]]
mountaintop removal mining (commonly referred to as mountaintop
mining), is administered by the U.S. Department of the Interior's
Office of Surface Mining (OSM). SMCRA permits for mountaintop removal
mining may be issued by the OSM or by individual States only if it has
been shown that the proposed mining activities will satisfy general
performance standards applicable to all surface coal mining operations.
In the Appalachian States where mountaintop mining occurs, the SMCRA
regulatory program has been delegated by the Federal Government to
State agencies, except in Tennessee (Copeland 2005, p. 2). Among the
general performance standards, SMCRA addresses disturbances at the
mine-site and in associated offsite areas and approximate original
contour (AOC) requirements, as well as the quality and quantity of
water in surface and ground water systems both during and after surface
coal mining operations (Copeland 2005, p. 2).
Before commencing mountaintop removal mining, a coal company must
post a bond to pay for the reclamation of the site. To get this bond
released, the company must reclaim the site to meet the standards set
by the State responsible for implementing SMCRA. Reclamation at
mountaintop mine sites has focused on erosion prevention and backfill
stability and not on reclamation with trees. The compacted backfill
material that is normally used for reclamation hinders tree
establishment and growth. Furthermore, reclaimed soils are more
conducive for growing grasses, which outcompeted tree seedlings;
grasses are often planted as a fast-growing vegetative cover to reduce
erosion. As a result, natural succession by trees and woody plants on
reclaimed mined land (with intended post-mining land uses other than
forest) is slowed (Environmental Protection Agency 2005, p. 4; Handel
et al. 2003, p. 12).
Section 404 of the Clean Water Act (33 U.S.C. 1251 et seq.) is
another principal environmental law involved in the regulation of
mountaintop mining. The section 404 permit program, which regulates the
discharge of dredge and fill material into waters of the United States,
applies to the disposal of excess overburden associated with
mountaintop mining. These permits are issued by the U.S. Army Corps of
Engineers with oversight by the U.S. Environmental Protection Agency.
In the past, the Corps of Engineers has generally permitted the
disposal of mountaintop mining fill under Nationwide Permit 21 (NWP
21). This overburden has frequently been deposited in adjacent stream
valleys in a process known as valley fill. This nationwide permit
authorizes discharges from surface coal mining activities that result
in no more than minimal impacts (site-specifically and cumulatively) to
the aquatic environment.
Cerulean warblers and their habitat are impacted by mountaintop
mining both by the clearing of forests to remove the coal and by the
associated disposal of mine overburden in adjacent valleys. In
addition, the practice of establishing non-forested habitats,
especially grasses, on reclaimed mine lands that were previously
forested has further prevented the restoration of cerulean warbler
habitat at these sites. The conservation of the cerulean warbler could
be improved by additional focus by the regulatory programs under SMCRA
and section 404 of the CWA on the additional protection and improved
reclamation of the species' habitat.
The U.S. Department of the Interior (National Park Service and Fish
and Wildlife Service) manages lands containing cerulean warblers. The
National Park Service Organic Act (39 Stat. 535; 16 U.S.C. 1, 2, 3, and
4), states that the NPS will administer areas under their jurisdiction
``* * * by such means and measures as conform to the fundamental
purpose of said parks, monuments, and reservations, which purpose is to
conserve the scenery and the natural and historical objects and the
wildlife therein and to provide for enjoyment of the same in such
manner and by such means as will leave them unimpaired for the
enjoyment of future generations.'' Several National Parks are known to
contain cerulean warbler populations and habitat.
The National Wildlife Refuge System Administration Act (NWRSAA; 16
U.S.C. 668d-668e) provides guidelines and directives for administration
and management of all areas in the National Wildlife Refuge System.
National Wildlife Refuges (NWR) are managed for species conservation,
consistent with the direction of the NWRSAA, as amended, and related
Service policies and guidance.
The Sikes Act (16 U.S.C. 670a-670o; 74 Stat 1052) authorizes the
Secretary of Defense to develop cooperative plans for conservation and
rehabilitation programs on military reservations and to establish
outdoor recreation facilities. Under the authority of the Sikes Act,
military installations prepare Integrated Natural Resources Management
Plans (INRMP) that address how fish and wildlife resources will be
managed. These plans reflect the mutual agreement of the military
facility, the Service, and the appropriate State fish and wildlife
agency on the conservation, protection and management of fish and
wildlife resources.
Executive Order 13186 (entitled Responsibilities of Federal
Agencies To Protect Migratory Birds), signed by President Clinton on
January 10, 2001, addresses the commitment by all Federal departments
and agencies to conserve migratory birds in the United States.
Executive Order 13186 directs Federal agencies that implement actions
having a measurable negative effect on migratory bird populations to
develop and implement a Memorandum of Understanding with the Service
that will promote migratory bird conservation. The Executive Order
identifies 15 conservation measures that each Federal agency is
encouraged to implement. These measures involve a range of actions to
be implemented by Federal agencies, including: (1) Integrating
migratory bird conservation into agency plans, programs, and actions,
including environmental analyses under NEPA; (2) adopting principles
and practices in the design of agency actions that avoid or minimize
adverse impacts on migratory birds; (3) incorporate comprehensive
migratory bird programs, such as Partners-In-Flight, North American
Waterfowl Management Plan, and North American Bird Conservation
Initiative into agency management plans and guidance; (4) restore and
enhance migratory bird habitat; (5) develop partnerships with non-
Federal entities to further bird conservation; and (6) promote research
and information exchange related to migratory birds, including
coordinated inventorying and monitoring on agency lands. The first two
Memorandum of Understandings under EO 13186, with the Department of
Defense and Department of Energy, were signed on July 12, 2006.
(2) Canadian Federal and Provincial Laws and Regulations
All migratory birds (including cerulean warblers), nests, eggs, and
their parts in Canada are protected by the Migratory Bird Conservation
Action of 1994, as amended. This law is similar to the Migratory Bird
Treaty Act in that it prohibits the taking, possession, transportation,
and sale of migratory birds and establishes penalties for violations,
but it provides no direct protections for migratory bird habitats. This
Canadian law implements the 1916 Convention between the United States
and Great Britain (for Canada) for the protection of migratory birds.
In Canada and the two Provinces where the species occurs (Ontario
and Quebec), the cerulean warbler is a
[[Page 70730]]
Species of Special Concern under schedule 1 of the Species at Risk Act
(Canada Gazette, Part III, Chapter 29, Vol. 25, No. 3 2002). Passed in
2002, the Species at Risk Act (SARA) is similar to the Endangered
Species Act. Under SARA, a Species of Special Concern is a ``wildlife
species that may become a threatened or an endangered species because
of a combination of biological characteristics and identified threats''
(section 2, Species at Risk Act, 2002). Only those species listed as
endangered, threatened, or extirpated are protected by the prohibitions
of SARA. The prohibitions and other regulatory provisions of SARA do
not apply to Species of Special Concern; however, SARA does require the
preparation of management plans for Species of Special Concern,
including measures for the conservation of the species and its habitat
(SARA, sections 65-72). The objective of implementing these management
plans is to prevent Species of Special Concern from becoming a
threatened or endangered species.
(3) State Laws
All of the 33 States within range of the cerulean warbler have
provisions in their Wildlife Codes that protect non-game migratory
birds, including the cerulean warbler. These State laws generally
prohibit the killing, capture, possession, and sale of migratory birds
without proper authorization from the State wildlife agency. Delaware
and Rhode Island list the cerulean warbler as a State Endangered
Species and the species is listed as a State Threatened Species in
Illinois and Wisconsin. The designation as Endangered or Threatened by
these States provides additional protection, prohibitions, and
conservation emphasis in accordance with their respective State
Wildlife Codes. Tennessee has designated the cerulean warbler as a
Species in Need of Management, which provides some additional
protection and conservation emphasis. Eleven States have placed the
cerulean warbler in a category of Species of Special Concern, Species
of Special Interest, or Rare. In most of these States, these categories
do not provide the cerulean warbler additional protection or
prohibitions beyond what is in their general Wildlife Codes. The
protections provided the cerulean warbler by the State wildlife laws
generally do not include regulatory provisions to protect its habitat.
Summary of Factor D
We believe those existing laws, regulations, and Executive Orders
that involve the management of Federal forest and wildlife resources
(MUSY, NFMA, National Wildlife Refuge System Administration Act,
National Park Service Organic Act, Sikes Act, and Executive Order
13186) are not inadequate mechanisms to conserve the cerulean warbler
and its habitat on these specific Federal lands. These laws provide the
flexibility and framework to maintain or adjust habitat management
objectives that benefit the cerulean warbler. Although these laws and
regulations contain sufficient provisions for the conservation of the
cerulean warbler, there are limitations in the ability of agencies to
implement them in a manner most beneficial to the species they are
intended to benefit or protect (for example, cerulean warblers). For
instance, limited agency budgets, conflicting policies, lack of public
support, and other factors can deter achieving the full management
flexibility and benefits.
As discussed above, we believe that certain existing laws
pertaining to the management of specific Federal lands in the United
States are not inadequate regulatory mechanisms to conserve the
cerulean warbler and its habitat. We also believe that some existing
regulatory mechanisms are inadequate in protecting the cerulean warbler
and its habitat. An example of this is the continued loss, without
adequate reclamation, of cerulean warbler breeding habitat from
mountain top mining, despite the application of the Surface Mining
Control and Reclamation Act and section 404 of the Clean Water Act to
these actions. Besides the regulation of mountain top mining under
SMCRA and section 404 of the Clean Water Act, we are not aware of any
Federal or State regulatory mechanisms that provide for the
conservation of cerulean warbler habitat on the extensive private
forest lands within the species' breeding range. Furthermore, we are
not aware of any laws that protect the cerulean warbler or its habitat
in its non-breeding (winter) range in South America.
E. Other Natural or Manmade Factors Affecting Its Continued Existence
We identified several other potential threats, but available
information is insufficient to determine that these factors have
contributed to or will likely cause a population level decline in
cerulean warblers. These factors are:
Mortality From Collisions With Structures
The collision of birds with structures during migration has been
well documented, especially since this issue began receiving major
emphasis in the 1970s (Manville in press, p. 2). Structures that pose a
collision hazard to birds include buildings, communication towers
(cell, radio, and television), wind power turbines, smoke stacks, and
power lines. There is no confirmed, validated number or accurate
estimate of the total number of birds killed by these structures, but
estimates range from four to five millions of birds up to 40 million
(Shire et al. 2000, p. 3; Manville in press, p. 3). Few studies have
been carried out to document cerulean warbler mortalities from tall
structures. The analysis by Shire et al. (2000, p. 9) of 149 reports of
tower-caused mortalities identified 164 cerulean warblers killed at 5
sites. At this time, there have been insufficient studies conducted for
the Service to be able to evaluate the threat of tall structures to
cerulean warblers.
Localized Areas of Calcium Depletion Because of Acid Rain
Atmospheric acid deposition (acid rain) has been linked with
reduced abundance of some songbird species (Hames et al. 2002, pp.
11238-11239; Hames et al. 2006). Under some conditions, calcium, which
is needed for egg production, is leached from basic soils. Researchers
have not studied the potential effect of this phenomenon on cerulean
warblers.
Reduction in Prey Availability Because of Climate Change
Evidence from Europe indicates that climate change may advance the
phenology of insect populations in temperate regions, and the peak in
insect prey abundance may therefore occur before long-distance
migratory birds arrive from the tropics, and prior to their need for
abundant food for their young (Both et al. 2006, pp. 81-82; and Both
and Visser 2001, pp. 296-298). We know of no information that indicates
this is currently a problem for cerulean warblers.
Small Population Phenomena
We found no evidence that genetic isolation (Veit et al. 2005) or
other phenomena associated with small populations are affecting
cerulean warblers.
Extinction Risk Analysis
Since our knowledge of the factors that may lead to extinction is
incomplete, and because extinction is inherently a probabilistic event
(it may or may not happen at any specified time due to random events),
extinction risk is best described by a likelihood or probability. The
most direct method available to estimate extinction likelihood for
cerulean warblers is to
[[Page 70731]]
calculate forward from the current total abundance using the average
annual trend in abundance. The best available estimate for current
global population size of cerulean warblers is based on the Partners in
Flight estimate of 560,000 birds in 1995 (Rich et al. 2004, Appendix
A--pp. 69-77), decreased by 11 years of declines that average 3.2
percent annually, resulting in an estimate of about 390,000 birds in
2006. Although the Partners in Flight estimate was imprecise (plus or
minus 50 percent of the estimate) and may also be biased, most likely
underestimating abundance (see Population Size Estimate Based on the
Partners in Flight Method above), it is the best available data at the
time of this finding. Expressed as a more general figure that reflects
the substantial uncertainty about actual population size, we conclude
that the current population of cerulean warblers may be around a half-
million birds, and perhaps much larger. For the extinction risk
analysis that follows, however, an estimate of 400,000 birds was used
for 2006.
If the average 3.2 percent per year decline continues without
variance, a population of 400,000 birds will decrease to approximately
200,000 in 20 years, 80,000 in about 50 years, and 15,000 in 100 years.
In reality, population trends vary from year to year so future
population change could be greater or less than these median or
``deterministic'' estimates. Thogmartin (2006, pp. 3-4) applied a
statistical method called diffusion approximation (described in Dennis
et al. 1991, and Holmes 2001, 2004) to the BBS data to estimate the
probability of cerulean warbler population change to different levels
over time. This method requires estimates for initial population size,
average annual trend, and the year-to-year variance in population
counts to project a statistical distribution of potential future
population sizes over time--given the key assumption that past year-to-
year fluctuations represent the plausible range (a statistical
distribution) of annual changes that can happen randomly in the future.
Given the available 40-years of BBS abundance indices and assuming the
current population size is nearly 400,000 birds, Thogmartin (2006, p.
18) projected an 83 percent chance that the population will decrease to
40,000 birds (90 percent decline) in 100 years. The likelihood of
extinction, modeled as a 99.999 percent population reduction or a
decline to a few hundred birds, was close to zero in 100 years
(Thogmartin 2006, p. 18). To date, there have been no published
diffusion approximation models or other extinction risk analyses for
the cerulean warbler. Therefore, the work conducted by Thogmartin
(2006) is the best scientific information currently available on this
topic.
Thogmartin (2006, p. 19) subsequently evaluated whether the
likelihood of population declines was sensitive to the uncertainty
about current population size. He found that the estimated
probabilities of declines differed for projections using the upper and
lower ends of the interval estimated by Partners in Flight extrapolated
to 2006, that is, 200,000 or 600,000 birds rather than the median or
``best'' estimate of 400,000 birds.
Thogmartin (2006, p. 20) also completed calculations for the
eastern or Appalachian portion of the species' range separately from
the regions farther west to consider possible regional differences.
Initial population in the east (Bird Conservation Regions 13 and 27 to
30) was 345,000 birds (86 percent of total abundance), and in the west
(Bird Conservation Regions 22 to 25) it was 55,000 birds (14 percent of
total abundance) (relative abundance between regions from Partners in
Flight figures; Rich et al. 2004, Appendix A--pp. 69-77). Projected
likelihood of a 90 percent decline in 100 years in these two regions
was about 70 percent and 90 percent, respectively (Thogmartin 2006, p.
20). The projected risk of decline was actually lower for the
Appalachian region alone than for the species rangewide due to
relatively less year-to-year variance in counts in this higher density
area compared with the estimates that include very small sample size
counts in the western parts of the range.
These calculations are helpful in understanding the consequences of
a continuation of the historical trend, but they do not address whether
underlying population dynamics will differ as time passes. The 100-year
time frame in Thogmartin's (2006) analysis is simply a convention from
theoretical modeling (e.g., Dennis et al. 1991, and Holmes 2001, 2004)
and does not address the reliability of projecting that far forward
based only upon historical data. It is clear that the farther into the
future we attempt to predict, the less confident we can be that the
historical trend will persist. Future population sizes will vary due to
a variety of factors, both random events and progressive changes in
causal environmental factors that we cannot foresee at this time. Thus
we are more confident that the historical trends will continue over the
next few decades, than over longer time frames such as 100 years.
Determination of Status Under the Endangered Species Act
The Act defines an endangered species as ``any species which is in
danger of extinction throughout all or a significant portion of its
range * * *'' (16 U.S.C. 1533 Sec. 3(6)). The Act defines a threatened
species as ``any species which is likely to become an endangered
species within the foreseeable future throughout all or a significant
portion of its range'' (16 U.S.C. 1533 Sec. 3(20)). For each species
considered for listing, the Service must review the best available
information on the likelihood of extinction over time and determine
case-by-case whether the present risk is sufficient to constitute a
``danger'' of extinction, or whether projected future risk is
``likely'' to become a danger of extinction under ``foreseeable''
conditions.
The cerulean warbler has been declining by about 3 percent
annually, on average, for the last 40 years, including within the
Appalachian core breeding area (see Population Size and Trends). The
biological factors most likely to have caused this trend include: (1)
Reduction in available nesting sites and suitable breeding territory
characteristics because of loss or degradation of nesting habitat; (2)
reduction in foraging success resulting from decreased prey abundance,
primarily on the wintering ground in South America; (3) increased
predation throughout the species' annual range and nest parasitism of
cerulean warblers in the breeding grounds resulting from habitat
fragmentation; and (4) increased mortality during migration due to
coastal forest habitat loss (see The Present or Threatened Destruction,
Modification, or Curtailment of Its Habitat or Range). The Service
further concludes that those factors are ongoing and thus will likely
continue to cause the species to decline, probably at a similar rate,
as in the recent past. The best available projection for future trends
is to assume that the persistent rate of decline documented by the BBS
over the past 40 years will continue within the estimated credible
interval, between 2.0 and 4.2 percent per year.
Since projections derived from the BBS data indicate effectively no
chance for this species to become extinct in the next 100 years unless
conditions change beyond what we can anticipate (see Extinction Risk
Analysis above), we do not believe this species is likely to become
endangered within the foreseeable future. In short, a species with a
current population of perhaps half a million birds and quite possibly
more, declining chronically by 2 to 4
[[Page 70732]]
percent annually, is neither in danger of extinction now or likely to
become in danger of extinction in the future that we can reasonably
foresee. Thus, the Service concludes that the cerulean warbler does not
presently qualify for protection as an endangered species or a
threatened species under the Act and the petitioned action is not
warranted.
Summary
The cerulean warbler population is decreasing by approximately
three percent per year across its breeding range. A combination of
habitat losses and structural changes and fragmentation in remaining
forest habitats across the species' annual range are most likely the
primary causal factors contributing to this decline. The available
information on potential causal factors indicates these threats are,
for the most part, both already operating and will continue to operate
in the foreseeable future. Hence, we anticipate continued, gradual
decline of this species. We also conclude, however, that abundance will
remain high enough that the species effectively is in no danger of
extinction in the near term, and that, if the historical trend
continues, tens of thousands of cerulean warblers will remain in 100
years.
The Act defines an endangered species as a species in danger of
extinction in all or a significant portion of its range. Given the
available information including a population size approaching half a
million, perhaps more, cerulean warblers are not currently facing
extinction across their range. We do not consider the westernmost parts
of the range, where local extirpation could possibly occur in the next
few decades, as significant from the perspective of defining the entire
species as endangered, because those portions already contain only a
small fraction of the total population and their loss would not put the
remainder of the range at risk of extinction. Therefore, those
westernmost areas are not a significant portion of the species' range.
A threatened species, as defined in the Act, is a species likely to
become endangered in the foreseeable future in all or a significant
portion of its range. We do not believe that it is likely (more likely
to happen than not) that cerulean warblers will decline to a point
where they are endangered or facing extinction within the foreseeable
future. This is our conclusion, even if conditions were on the worst
end of the range for trends and abundance rather than the median or
'best' estimates indicated by 40 years of breeding bird surveys. Again,
we do not consider those portions of the range with currently marginal
populations that may become at risk of extinction in less than 100
years as significant to the entire species' projected extinction risk,
and thus they are not a significant portion of the range as used in the
definition of threatened. Based on the trends recorded in breeding
population counts and the assumption that those declines and their
causal factors will continue unabated, the likelihood of species
extinction, even as far into the future as 100 years, appears close to
zero.
Finding
We have carefully assessed the best scientific and commercial
information available regarding the past, present, and future threats
faced by the cerulean warbler. We reviewed the petition, available
published and unpublished scientific and commercial information, and
information submitted to us during the public comment period following
our 90-day petition finding. This finding reflects and incorporates
information we received during the public comment period and responds
to significant issues. We also consulted with recognized experts on the
cerulean warbler and its habitat from Federal and State agencies, non-
governmental conservation organizations, academia, and the forest
industry. On the basis of this review we have determined that the
listing of cerulean warbler as threatened or endangered is not
warranted under the Endangered Species Act, as amended.
If new impacts to the species arise in the future or if the Service
finds that the populations are declining significantly faster than they
were found to have done in the past or that threats are of greater
magnitude than they are currently, the Service can reexamine the
listing status of the cerulean warbler. We will continue to monitor the
status of the cerulean warbler and its habitat and will continue to
accept additional information and comments from all governmental
agencies, the scientific community, industry, or any other interested
party concerning this finding.
Future Conservation
Even though we have determined in this 12-month petition finding
that the cerulean warbler does not meet the definition of endangered or
threatened, we believe it is essential that existing conservation
efforts for the cerulean warbler be pursued and new actions implemented
to address the steady decline of the species. Besides the ongoing
conservation efforts addressed under Factor A of this finding, there
are several important emerging efforts and programs, all involving
multiple, diverse partners. We did not rely on these future
conservation actions in our determination that listing the cerulean
warbler is not warranted and, therefore, we did not evaluate them under
our 2003 Policy for Evaluation of Conservation Efforts When Making
Listing Decisions (68 FR 15100; March 28, 2003).
In 2005, the Service's Migratory Bird Program initiated a new
strategy to better measure its success in achieving its bird
conservation priorities and strategies. The Focal Species Strategy
involves campaigns for selected species to provide explicit, strategic,
and adaptive sets of conservation actions required to return species to
healthy and sustainable levels. The Service's list of Birds of
Management Concern is a subset of species protected by the MBTA that
pose special management challenges due to a variety of reasons. There
are currently 412 species, subspecies, or populations of birds on the
Birds of Management Concern list, including the cerulean warbler.
Through a comprehensive review of the birds on this list and using a
combination of evaluation factors, the Service's Migratory Bird Program
identified 139 bird species for the development of Focal Species
Strategies. The cerulean warbler is in the first group of birds to have
focal species strategies developed in Fiscal Years 2005 and 2006. The
cerulean warbler Focal Species Strategy, the first draft of which is
scheduled to be completed in September 2006, will utilize management
and conservation documents to form an action plan (a species-specific
mix of monitoring, research, assessment, habitat and population
management, and outreach) necessary to accomplish: (1) Desired status;
(2) a summary of the responsibilities for actions within and outside
the Migratory Bird Program; (3) a focus of Service resources on
implementing those actions; and (4) communications to solicit support
and cooperation for partners inside and outside the Service. The
engagement of partners and stakeholders is essential for developing and
implementing this focal species strategy for the future conservation of
the cerulean warbler. The Service's Migratory Bird Program has involved
cerulean warbler experts and other partners in identifying the future
desired status and priority conservation measures for the focal species
strategy. The Cerulean Warbler Focal Species Strategy will provide an
important ``blueprint'' for use by Federal and State agencies,
conservation organizations, researchers, corporations, private
landowners, groups like the
[[Page 70733]]
Cerulean Warbler Technical Group (see below), and other bird
conservation programs, such as the Important Bird Areas, in
implementing actions for the conservation of the cerulean warbler.
BirdLife International's Important Bird Areas Program (administered
by the National Audubon Society in the United States) identifies,
monitors, and conserves a global network of Important Bird Areas (IBA)
that provide important habitat for birds and focuses conservation
efforts at these sites. The IBA Program recognizes that habitat loss
and fragmentation are the most serious threats facing populations of
birds. By working through partnerships, principally the North American
Bird Conservation Initiative, to identify those places that are
essential to birds, the National Audubon Society and its many IBA
partners hope to minimize the effects of habitat loss on birds. The
identification and inventory of IBAs has been a particularly effective
way to prioritize conservation efforts. IBAs are key sites for
conservation, often able to be conserved in their entirety and often
already part of a conservation-area network. There are approximately
112 IBAs in the United States and six in the Canadian Province of
Ontario that contain the cerulean warbler. Several of these IBAs
contain large cerulean warbler populations and important breeding
habitats (for example, Northern Montezuma Wetlands IBA in New York and
Southern Cumberland Mountains IBA in Tennessee). Within the cerulean
warbler's wintering range, there are 30 IBAs that contain the species
(14 in Colombia, 14 in Venezuela, and 2 in Ecuador).
The State Wildlife Grants Program (SWG; administered by the
Service's Federal Assistance Program), provides Federal funds to every
State and territory for the development and implementation of programs
that benefit wildlife and their habitat, including species that are not
hunted or fished. A primary focus of the SWG Program is to target funds
to States to implement conservation actions for rare or declining
wildlife species to prevent these species from becoming endangered in
the future. To be eligible for these funds, States and territories were
required to submit to the Service by October 1, 2005, a State Wildlife
Action Plan (also called a Comprehensive Wildlife Conservation
Strategy) that, at a minimum, addressed the following seven items: (1)
Information on the distribution and abundance of wildlife species,
including low and declining populations, that are indicative of the
diversity and health of the State's wildlife; (2) descriptions of
locations and relative condition of key habitats and community types
essential to conservation of these species; (3) descriptions of
problems which may adversely affect these species; (4) descriptions of
conservation actions proposed to conserve these species and habitats
and priorities for implementing actions; (5) proposed plans for
monitoring these species and their habitats; (6) descriptions of
procedures to review the Plan; and (7) plans for coordinating the
development, implementation, review, and revision of the Plan. In
appropriating funds for the SWG Program, Congress directed the States
to place appropriate priority on ``those species of greatest
conservation need''. In defining the species required by number 1
above, most State Wildlife Action Plans contain a list and description
of the Species of Greatest Conservation Need (SGCN).
All 33 States within the range of cerulean warbler have completed
their State Wildlife Action Plans. These plans have been reviewed and
approved by the Service. Of these States, 23 have identified the
cerulean warbler as a SGCN. In addition, nine States' Plans have
identified priority conservation and management objectives and actions
for the cerulean warbler. The actions in these nine Plans include
monitoring populations, managing forests to provide high-quality
nesting habitat, implementing measures to maintain appropriate habitat
patch size and reduce forest fragmentation, and collaborating with
others to conserve the species' wintering habitat in South America.
The integrated bird conservation efforts under the North American
Bird Conservation Initiative and Partners-In-Flight will benefit the
future conservation of the cerulean warbler. Concept Plans and Bird
Conservation Plans have been completed or are being developed in Bird
Conservation Regions (BCR) and Physiographic Areas that contain
cerulean warblers. These plans have specific actions pertaining to the
cerulean warbler, especially in the Appalachian Mountains Bird
Conservation Region. This BCR, encompassing 42 million ha (105 million
ac), contains the core breeding population of cerulean warbler and is
essential to the future conservation of the species. A future critical
need in this BCR is the establishment of a coordinator to integrate and
expand conservation actions for the cerulean warbler and other birds in
this region. The Partners-In-Flight program is addressing the decline
of the cerulean warbler and its habitat in both its breeding and non-
breeding range.
We believe these and other existing and emerging collaborative
efforts provide an excellent opportunity to reverse the steady decline
of the cerulean warbler and preclude the future need to list. The
Service believes it is important to continue strong support for
monitoring efforts for this species, especially long-term monitoring
programs like the Breeding Bird Survey that provides valuable trend
information. Tracking population changes is vital to the future
conservation of the cerulean warbler and other neotropical migratory
birds. We will provide strong support and develop partnerships around
the Service's Cerulean Warbler Focal Species Strategy, which will
become an important blueprint for helping to reverse the warbler's
population decline through proactive conservation efforts. We will also
continue to support and provide assistance to the Cerulean Warbler
Technical Group because it has the opportunity to effect positive
change for the species through its scientifically driven collaborative
efforts. We will support and provide technical assistance in using the
other integrated bird conservation programs (Partners-In-Flight, North
American Bird Conservation Initiative, and Important Bird Areas) and
the State's Wildlife Action Plans to further promote the future
conservation of the cerulean warbler.
References
A complete list of references used in the preparation of this
finding is available upon request from Columbia Ecological Services
Field Office (see ADDRESSES) or can be downloaded from our Web site at
http://www.fws.gov/midwest/eco_serv/soc/.
Author
This finding was written by biologists from the Service's
Endangered Species and Migratory Bird Programs in Region 3, 4, and 5
and Washington, DC.
Authority
The authority for this action is the Endangered Species Act of
1973, as amended (16 U.S.C. 1531 et seq.).
Dated: November 28, 2006.
Kenneth Stansell,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. E6-20530 Filed 12-5-06; 8:45 am]
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