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Recovery of the Chesapeake Bay Bald Eagle Nesting Population

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Abstract We conducted annual aerial surveys throughout the tidal reach of the Chesapeake Bay, USA, between 1977 and 2001 to estimate population size and reproductive performance for bald eagles (Haliaeetus leucocephalus). The population increased exponentially from 73 to 601 pairs with an average doubling time of 8.2 years. Annual population increase was highly variable and exhibited no indication of any systematic decline. A total of 7,590 chicks were produced from 5,685 breeding attempts during this period. The population has exhibited tremendous forward momentum such that >50% of young produced over the 25-year period were produced in the last 6 years. Rapid population growth may reflect the combined benefits of eliminating persistent biocides and active territory management. Reproductive rate along with associated success rate and average brood size increased throughout the study period. Average reproductive rate (chicks/breeding attempt) increased from 0.82 during the first 5 years of the survey to 1.50 during the last 5 years. Average success rate increased from 54.4% to >80.0% during the same time periods. The overall population will likely reach saturation within the next decade. The availability of undeveloped waterfront property has become the dominant limiting factor for bald eagles in the Chesapeake Bay. Maintaining the eagle population in the face of a rapidly expanding human population will continue to be the greatest challenge faced by wildlife biologists.
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Management and Conservation Article
Recovery of the Chesapeake Bay Bald Eagle
Nesting Population
BRYAN D. WATTS,
1
Center for Conservation Biology, College of William and Mary, Williamsburg, VA 23187-8795, USA
GLENN D. THERRES, Maryland Department of Natural Resources, Wildlife and Heritage Service, Annapolis, MD 21401, USA
MITCHELL A. BYRD, Center for Conservation Biology, College of William and Mary, Williamsburg, VA 23187-8795, USA
ABSTRACT We conducted annual aerial surveys throughout the tidal reach of the Chesapeake Bay, USA, between 1977 and 2001 to
estimate population size and reproductive performance for bald eagles (Haliaeetus leucocephalus). The population increased exponentially from 73
to 601 pairs with an average doubling time of 8.2 years. Annual population increase was highly variable and exhibited no indication of any
systematic decline. A total of 7,590 chicks were produced from 5,685 breeding attempts during this period. The population has exhibited
tremendous forward momentum such that .50%of young produced over the 25-year period were produced in the last 6 years. Rapid
population growth may reflect the combined benefits of eliminating persistent biocides and active territory management. Reproductive rate
along with associated success rate and average brood size increased throughout the study period. Average reproductive rate (chicks/breeding
attempt) increased from 0.82 during the first 5 years of the survey to 1.50 during the last 5 years. Average success rate increased from 54.4%to
.80.0%during the same time periods. The overall population will likely reach saturation within the next decade. The availability of
undeveloped waterfront property has become the dominant limiting factor for bald eagles in the Chesapeake Bay. Maintaining the eagle
population in the face of a rapidly expanding human population will continue to be the greatest challenge faced by wildlife biologists.
(JOURNAL OF WILDLIFE MANAGEMENT 72(1):152–158; 2008)
DOI: 10.2193/2005-616
KEY WORDS bald eagle, Chesapeake Bay, Haliaeetus leucocephalus, population recovery, reproductive rates.
Since the ban on DDT and like compounds in 1972, bald
eagle (Haliaeetus leucocephalus) populations have exhibited
dramatic growth throughout their breeding range. Bald
eagles throughout the conterminous United States have
increased from an estimated low in 1963 of 417 pairs
(Sprunt 1963) to an estimated 5,748 pairs by 1998 (Millar
1999). This represents an average annual increase of nearly
8%despite the fact that some populations did not show
appreciable growth until the early 1980s (Buehler 2000). In
response to the dramatic increases in population size,
productivity, and distribution, the bald eagle was reclassified
from endangered to threatened in 1995 by the United States
Fish and Wildlife Service (Millar 1995) and was proposed
for removal from the federal list of threatened and
endangered species in 1999 (Millar 1999).
The Chesapeake Bay area, USA, was 1 of 5 regions
established in the mid-1970s for the recovery of the bald
eagle. Biologists within the Bay have had a long history of
work with eagles since the first ground survey was conducted
in 1936 (Tyrell 1936). There was an estimated 600–800
nesting pairs in the 1930s. Surveys have been conducted
annually for .45 years beginning with ground surveys in
1956 (Abbott 1957) and continuing with aerial surveys since
1962 (Abbott 1963, 1976; Sprunt 1963). By 1962 the
nesting bald eagle population had declined to 150 pairs with
a productivity rate of only 0.2 young per active nest. By 1970
there were only 80–90 pairs in the Chesapeake Bay area.
In 1977 the United States Fish and Wildlife Service
formed the Chesapeake Bay Bald Eagle Recovery Team
(Abbott 1977). This team was tasked with developing a plan
for the recovery of the Bay population. As part of this
process, state wildlife agencies assumed the responsibility for
population monitoring. The 2001 breeding season repre-
sented the 25th year of the comprehensive bald eagle
breeding survey under the coordination of the respective
state agencies. The purpose of this paper is to present the
results of this 25-year period and to discuss findings with
respect to regional recovery goals and the future of the
population.
STUDY AREA
Our study area included the entire tidal reach of the
Chesapeake Bay (Fig. 1). The Chesapeake Bay is the largest
estuary in the United States, containing .19,000 km of
tidal shoreline. The Bay’s wide salinity gradient, shallow
water, and climate have made it one of the most productive
aquatic ecosystems in North America. Bald eagles breed
throughout the estuary from the Atlantic Ocean to the fall
line. The fall line is an erosional scarp where the
metamorphic rocks of the Piedmont meet the sedimentary
rocks of the Coastal Plain. The geologic formations along
this boundary frequently determine the landward extent of
tidal influence. Forest cover has varied dramatically since
European settlement, reaching a low of 50%in the late
1800s, but is now the dominant land cover except in areas
with intensive agriculture (Brush 2001). Forest composition
forms a pine–hardwood gradient throughout the Bay with
pine-dominated forests on the outer Coastal Plain to
hardwood-dominated forests on the inner Coastal Plain.
Pine forests are dominated by loblolly pine (Pinus taeda) and
mixed hardwoods are dominated by various oaks (Quercus
spp.), red maple (Acer rubrum), American beech (Fagus
grandifolia), and tulip poplar (Liriodendron tulipifera). The
Bay supports a diverse fish community that has been the
1
E-mail: bdwatt@wm.edu
152 The Journal of Wildlife Management 72(1)
basis of significant commercial fisheries (Murdy et al. 1997).
The Chesapeake Bay and its adjacent uplands are under
increasing pressure for growth and development. The
human population within counties adjacent to the tidal
reach of the Bay has increased from 1.63 million people in
1900 to 3.81 million people in 1950 to 8.06 million people
in 2000 (http://www.census.gov). This growth is expected
to continue into the foreseeable future (Gray et al. 1988),
placing increasing pressures on the Bay and its natural
resources.
METHODS
We have systematically surveyed the entire study area for
breeding bald eagles since spring 1977 via a standard 2-
flight approach (Fraser et al. 1983). We conducted the first
flights between late February and the end of March to locate
breeding territories. We used a Cessna 172 or 180 aircraft to
systematically over-fly the land surface at an altitude of
approximately 100 m to detect eagles and nests. We
maneuvered the aircraft between the shoreline and a
distance of 1–3 km to cover the most probable breeding
locations. Survey effort and coverage was consistent
throughout the study period. We plotted nests detected on
7.5-minute topographic maps and gave them unique alpha-
numeric codes. We examined each nest to determine its
condition and status. We considered a breeding territory to
be occupied if we observed a pair of birds in association with
the nest and there was evidence of recent nest maintenance
(e.g., well-formed cup, fresh lining, structural maintenance).
We considered nests to be active if we observed a bird in an
incubating posture or if we detected eggs or young in the
nest (Postupalsky 1974). We conducted the second survey
flights from late April through May to check occupied nests
for productivity and to recheck occupied territories for
breeding. We flew a plane low over the nest, allowing
observers to examine nest contents and record the number of
eaglets.
Previous authors (e.g., Fraser 1978, Steenhof and Kochert
1982, Fraser et al. 1984, Steenhof 1987) have outlined
several potential sources of bias inherent in the 2-flight
survey for raptor populations. One such source arises from
pairs that make breeding attempts, but fail prior to the first
survey flight. This bias serves to both underestimate the
nesting population and inflate the per capita reproductive
rate. In this study, we used the number of territories
determined to be occupied rather than the number of nests
with eggs to represent the breeding population. Although
this parameter is subject to similar concerns, we feel that it is
more robust with respect to this source of sampling error. A
second source of error stems from using a single productivity
flight within an asynchronous population. When used alone,
a single survey records chicks from a cross-section of ages
and assumes no mortality. The error associated with this
assumption serves to overestimate fledging success since
some young chicks do not to survive to fledging age. We
have not corrected for this source of error.
We defined breeding success as the percentage of occupied
nests that contained 1 young, reproductive rate as the
number of young per occupied nest, and average brood size
as the number of young per successful nest. We expressed
population growth rate using the average time (in yr)
required for the population to double in size (t
double
), the
intrinsic rate of increase (r), and the average annual percent
increase over the study period. We calculated average
doubling time using the growth equation N
t
¼N
0
e
rt
where
N
t
is the population size in 2001, N
0
is the population size
in 1977, eis the base of the natural logarithm, ris the
intrinsic rate of increase, and tis the time interval between
population estimates. With this configuration, t
double
¼
ln(2)/r. We calculated average annual percent increase as
(N
tþ1
N
t
)/N
t
3100.
RESULTS
Between 1977 and 2001, the bald eagle breeding population
in the tidal reach of the Chesapeake Bay increased from 73
pairs to 601 pairs (Table 1). During this period, the
population grew exponentially with an average doubling
time of 8.2 years. Intrinsic rate of increase (r) was 0.084.
Average annual increase was 9.4 61.11%(x¯ 6SE). The
annual population increase, as expressed by a percentage,
was highly variable over the study period and ranged from a
low of 2.2%(1998–1999) to a high of 22.0%(1989–1990).
There is no indication over the survey period that this rate
has shown any directional change (R
2
¼0.045, F[1,22] ¼
1.034, P¼0.429).
During the study period, we documented 5,685 breeding
attempts that produced 7,590 young (Table 1). Average,
annualized rates were 70.7 62.12%, 1.19 60.554, and 1.7
60.03 for breeding success, reproductive rate, and brood
size, respectively. The population has exhibited tremendous
Figure 1. We surveyed bald eagles within the Chesapeake Bay, USA
(1977–2001). We did not include areas outside of the tidal reach of the Bay
watershed in this study.
Watts et al. Chesapeake Bay Eagles 153
forward momentum such that .50%of young produced
over the 25-year period have been produced in the 6 years
since 1995.
Per capita reproductive rates increased significantly over
the study period (R
2
¼0.72, F[1,23] ¼58.4, P,0.001; Fig.
2). Reproductive rates averaged 0.82 60.058 for the period
1977 to 1981 compared to 1.50 60.032 for the period 1997
to 2001. The specific form of this increase may not be simple
linear. It appears that reproduction has shown a general
increase since the 1970s, but also experienced a perturbation
in the early 1990s (Fig. 2). The overall increase in per capita
reproductive rate resulted from a significant increase in both
success rate (R
2
¼0.69, F[1,23] ¼50.7, P,0.001) and
average brood size (R
2
¼0.60, F[1,23] ¼33.8, P,0.001).
Average success rate increased from 54.4%for the period
1977 to 1981 to .80%for the period 1997 to 2001. Success
rate and average brood size are strongly and positively
correlated ([Spearman Rank correlation coeff.] r
s
¼0.837, P
,0.001; Fig. 3), suggesting that reproduction is regulated by
some factor that varies annually throughout the entire Bay.
Table 1. Bald eagle population size and productivity within the tidal reach of the Chesapeake Bay, USA (1977–2001).
Yr
Occupied
nests
Active
nests
Successful
nests Young
Successful/
occupied
a
Successful/
active
a
Young/
occupied
a
Young/
active
a
Young/
successful
a
1977 73 69 39 62 53.4 56.5 0.8 0.9 1.6
1978 83 79 40 55 48.2 50.6 0.7 0.7 1.4
1979 87 82 38 57 43.7 46.3 0.7 0.7 1.5
1980 90 82 47 68 52.2 57.3 0.8 0.8 1.4
1981 93 88 54 89 58.1 61.4 1.0 1.0 1.6
1982 105 101 61 94 58.1 60.4 0.9 0.9 1.5
1983 112 106 69 109 61.6 65.1 1.0 1.0 1.6
1984 120 114 73 124 60.8 64.0 1.0 0.9 1.7
1985 125 122 86 158 68.8 70.5 1.3 1.0 1.8
1986 131 127 95 179 72.5 74.8 1.4 1.1 1.9
1987 154 152 123 221 79.9 80.9 1.4 1.3 1.8
1988 171 169 137 247 80.1 81.1 1.4 1.4 1.8
1989 182 179 122 200 67.0 68.2 1.1 1.5 1.6
1990 222 212 161
b
298 74.2 77.8 1.4 1.5 1.9
1991 232 224 179 313 77.2 79.9 1.3 1.1 1.7
1992 274 267 189
b
317 69.2 71.1 1.2 1.4 1.7
1993 287 280 194 331 67.6 69.3 1.2 1.4 1.7
1994 307 276 193
b
337 63.1 70.2 1.1 1.2 1.7
1995 340 307 250
b
464 74.4 82.5 1.4 1.2 1.9
1996 377 348 267
b
490 72.8 79.0 1.3 1.2 1.8
1997 416 387 294
b
557 72.4 78.0 1.4 1.5 1.9
1998 462 415 318
b
563 70.0 78.1 1.2 1.4 1.8
1999 472 441 348
b
650 75.3 80.7 1.4 1.5 1.9
2000 513 487 402
b
758 79.3 83.6 1.5 1.6 1.9
2001 601 571 448
b
849 75.7 79.7 1.4 1.5 1.9
a
Based on nests with known outcome.
b
Final outcome of ,10 nests not determined and not included in totals.
Figure 2. Relationship between reproductive rate (chicks/active nest) and
year for bald eagles within the tidal reach of the Chesapeake Bay, USA
(1977–2001).
Figure 3. Relationship between average brood size and breeding success for
bald eagles within the tidal reach of the Chesapeake Bay, USA (1977–
2001).
154 The Journal of Wildlife Management 72(1)
DISCUSSION
The Chesapeake Bay bald eagle population has now
recovered to the size estimated during the 1930s (Tyrell
1936, Abbott 1978). Population size thresholds outlined in
the Chesapeake Bay Bald Eagle Recovery Plan (Byrd et al.
1990) for federal downlisting (175–200) and delisting (300–
400) were met in 1988 and 1992, respectively, for the
broader Chesapeake Bay Recovery Region (Millar 1995,
1999). The recovery region extends well beyond the
tributaries of the Chesapeake Bay and includes all of
Virginia, Maryland, Delaware, and New Jersey, as well as
portions of Pennsylvania and West Virginia, USA (Byrd et
al. 1990). Our study area typically supports 90–95%of the
population within the broader recovery region.
We documented an average annual rate of increase of
9.4%. Buehler et al. (1991a) used demographic data along
with a deterministic life-table model to predict population
growth for the Chesapeake Bay population. They estimated
minimum and maximum survival rates based on 39 eagles
that were monitored with telemetry and predicted a range of
population growth rates from 5.8%to 16.6%per year.
These predictions are in general agreement with the
observed growth rate of 9.4%reported here. Sensitivity
analysis revealed that model estimates were most sensitive to
changes in adult survivorship followed by subadult survivor-
ship. As expected, growth rates were relatively robust against
variation in nest success and reproductive rates.
Nesting success in the Chesapeake Bay may be the highest
on record in North America. Since 1995, 70%of occupied
territories produced 1 young. Success rates in many parts
of North America have ranged between 60%and 65%,
including the Pacific Northwest (Anthony et al. 1994,
Watson et al. 2002) and the Rocky Mountains (Swenson et
al. 1986, Kralovec et al. 1992). In Alaska (Stiedl et al. 1997)
and Arizona, USA (Driscoll et al. 1999) only half of nesting
pairs produced young.
The reproductive rate of Chesapeake Bay eagles is
comparable to or greater than those of other regions. The
highest reproductive rates have been in Florida, USA, where
nesting bald eagles produced 1.3 young per breeding pair
during 1997–2001 (Millsap et al. 2004) and Wisconsin,
USA, where eagles produced 1.3 young per occupied
territory in the mid 1980s (Kozie and Anderson 1991).
Productivity in the Rocky Mountain states has ranged from
1.0 to 1.2 young per nesting pair (Swenson et al. 1986,
Kralovec et al. 1992). Reproductive rates in the Pacific
Northwest were 0.9 young per occupied nest (Anthony et al.
1994, Watson et al. 2002). In Alaska, productivity (0.8
young/pair) was well below that in the Chesapeake Bay
(Stiedl et al. 1997). The lowest reproductive rate (0.13
young/pair) recorded in recent times was in Alaska on
Prince of Wales Island (Anthony 2001). That low rate was
attributed to high densities of nesting bald eagles. There is
no indication in the Chesapeake Bay that nesting densities
are reducing productivity rates yet.
A reproductive rate of 0.7 chicks per breeding attempt has
been suggested to represent the threshold for population
maintenance for bald eagles (Sprunt et al. 1973). Buehler et
al. (1991a) estimated that 1.0 chicks per successful nest
(equivalent to brood size) was required for population
maintenance in the Bay. A reproductive rate of 1.1 chicks
per breeding attempt was set as the recovery goal for the
Chesapeake Bay population (Byrd et al. 1990). Documented
rates for the Chesapeake Bay population reached an all-time
low of 0.2 chicks per breeding attempt in 1962 (Abbott
1963). Productivity showed a steady increase throughout the
late 1960s and early 1970s, reaching projected maintenance
levels by the mid-1970s (Abbott 1978). The population has
met or exceeded the productivity target outlined in the
recovery plan in every year since 1985. The reproductive rate
documented by Tyrrell in 1936 was nearly 1.5 chicks per
breeding attempt. The population has achieved this rate in 4
of the 5 years between 1997 and 2001.
We documented an increase in reproductive rates
throughout the period of this study. This increase resulted
from increases in both elements of reproduction including
the proportion of nesting attempts that were successful and
average brood size for successful nests. Gains in the early
portion of the study likely reflect the general recovery in
productivity that followed a reduction in contaminant use
within the Bay. The concentrations of DDE, dieldrin, and
PCBs in eggs from the Chesapeake Bay during 1973–1979
were among the highest for any bald eagle population in the
United States (Wiemeyer et al. 1984). However, dramatic
reductions in these contaminants were documented by the
mid-1980s (Wiemeyer et al. 1993). This time frame
corresponds to a time when many of the breeding
populations throughout the lower portion of the breeding
range began to show definitive signs of growth (Buehler
2000). Why reproductive rates have continued to rise after
the mid-1980s is less clear. It is possible that recent gains
reflect a continued lag in productivity as older adults with
higher contaminant loads in the population are replaced or
that some other demographic process is at work.
We documented a strong, positive correlation between
annual success rate and average brood size throughout the
Chesapeake Bay. This relationship shows that during good
years a larger portion of pairs are productive and that
productive pairs raised larger broods compared to poor years.
This pattern implies that annual variation in reproductive
rates may, at least in part, be regulated by factors that are
acting on a large geographic scale. While reproductive rates
in bald eagles are certainly responsive to spatial and temporal
variation in prey resources (e.g., Hansen 1987, Bortolotti
1989, Steidl et al. 1997), it is not likely that prey stocks
alone are responsible for this specific pattern. Fish are the
dominant prey used by bald eagles for brood-rearing in the
Chesapeake Bay (Wallin 1982, Markham 2004). The
Chesapeake Bay supports a diverse fish assemblage, but
interspecific synchrony in stocks is poor and intraspecific
cycles in stocks often vary tributary to tributary (Murdy et al.
1997). Annual variation in spring weather conditions
throughout the Bay may be a more likely explanation for
this pattern. A relationship between weather and produc-
Watts et al. Chesapeake Bay Eagles 155
tivity has been suggested for other eagle populations (e.g.,
Isaacs et al. 1983, Swenson et al. 1986). Wet conditions
throughout the spring have been suggested to influence
brood provisioning, growth rates, and reproductive success
in the lower Bay (Markham 2004). Extended periods of rain
both increase the exposure of broods and make hunting
more difficult. Depending on brood age, these factors may
result in brood reduction or failure.
Given the tremendous forward momentum currently
exhibited by the breeding population, it seems likely that
bald eagles will reach saturation within the Bay in a
relatively short period of time. No specific estimates of the
Chesapeake Bay bald eagle population are available prior to
the early 1900s. However, given the high productivity of
Bay waters and the availability of extensive shallow-water
foraging areas, it has been speculated that prior to European
settlement the Chesapeake Bay may have supported one of
the densest breeding populations of bald eagles outside of
Alaska. By applying breeding densities from Alaska to the
13,000 km of Chesapeake shoreline, Fraser et al. (1996)
suggested that the Chesapeake may have supported in excess
of 3,000 breeding pairs of bald eagles prior to European
Settlement. However, a recent investigation shows signifi-
cant spatial variation in both colonization rates and breeding
density, suggesting that carrying capacity varies widely
throughout the Bay (Watts et al. 2006). By fitting
population growth data (1977–2002) for birds in portions
of the lower Chesapeake Bay to a logistic curve, Watts et al.
(2006) estimated that the population had reached approx-
imately 70%of capacity. This suggests that the current
carrying capacity of the Bay may be half of that estimated by
Fraser et al. (1996) for the pristine Bay and that if recent
growth rates continue, this population should reach that
level within the next decade.
The availability of undeveloped waterfront property has
become the dominant limiting factor for bald eagles in the
Chesapeake Bay. Human activity is the best predictor of
eagle distribution within the tidal portion of the Bay.
Indicators of human activity such as housing and road
density, shoreline use, and boating activity have been related
to nest distribution (Watts et al. 1994), shoreline use
(Buehler et al. 1991b, Watts and Whelan 1997), and the
likelihood of nest abandonment (Therres et al. 1993) or
recolonization (B. D. Watts, College of William and Mary,
unpublished data). Since bald eagles began their most
dramatic decline in the 1950s, the human population within
the tidal reach of the Bay has increased by .50%(http://
www.census.gov). A preliminary review of development
occurring around eagle nests in the lower Chesapeake Bay
shows that development had occurred in 55%of shoreline
areas by the late 1980s (Byrd et al. 1990). Similarly, Buehler
et al. (1991b) found that in northern areas of the Bay,
75.6%of the shoreline had developments within 500 m.
Application of a habitat suitability model to the James River
in 1991 revealed that .50%of the available area was not
suitable for eagle breeding due to human use (Watts et al.
1994).
Increases in the human population around the Chesapeake
Bay are expected to continue for the foreseeable future
(Gray et al. 1988), likely causing further reductions in the
capacity of the Bay to support bald eagles. In the long term,
the size and stability of the breeding population will depend
on both the bald eagle’s capacity to cope with human activity
and the management community’s ability to protect suitable
breeding habitat. In Florida, Millsap et al. (2004) found
similar nest-occupancy rates and brood sizes between
suburban and rural nesting bald eagles. They defined
suburban nest sites as those with .50%intensive human
use within 1,500 m of the nest. Young per occupied nest site
averaged 1.3 in suburban nests between 1996 and 2001.
That is comparable to productivity of Chesapeake Bay bald
eagles during the same time period. Though few in number
as of 2001, bald eagles nesting in suburban situations are
increasing in the Chesapeake Bay area. Over the past
decade, the transition in the eagle population has been
ongoing with an increasing number of pairs breeding in very
disturbed settings. A recent investigation within the lower
Chesapeake Bay has shown that success rate and produc-
tivity for pairs within the most human-dominated settings
are not statistically distinguishable from pairs in the most
pristine settings (Watts 2006).
MANAGEMENT IMPLICATIONS
Banning of DDT and the application of management
guidelines by state and federal resource agencies have
resulted in a dramatic recovery of bald eagles in the
Chesapeake Bay. Despite successes, the eagle population
continues to be threatened by urban sprawl and associated
habitat loss. To date, the management community has not
been able to reach 50%of the habitat protection goal set in
the Chesapeake Bay Bald Eagle Recovery Plan (Byrd et al.
1990). Based on the current rate of land protection, the
increase in the human population, and the proximity of the
eagle population to capacity it appears unlikely that this goal
will ever be achieved, implying that the future of the
population will continue to depend on privately owned
lands. Broad land-use efforts, such as Maryland’s Ches-
apeake Bay Critical Area Program (Therres et al. 1988),
designed to help control shoreline development may be
critical in sustaining the population. Given the current rate
of land development along the shores of the Chesapeake
Bay, continued population and productivity monitoring is
needed to assess how bald eagles respond to habitat changes.
ACKNOWLEDGMENTS
The Maryland Department of Natural Resources, Virginia
Department of Game & Inland Fisheries, the United States
Fish and Wildlife Service, the United States Department of
Defense, and the United States Army Corps of Engineers
provided financial support for the annual survey. Federal
Aid in Wildlife Restoration grants and contributions to the
Chesapeake Bay and Endangered Species Fund also
provided funding. J. Abbott, K. Cline, F. Scott have
contributed a great deal to the survey. Regular survey pilots
156 The Journal of Wildlife Management 72(1)
have been S. Beck, C. and M. Crabbe, G. Lacey, and C.
Shermer. In addition to the authors, other biologists who
conducted numerous hours of aerial surveys during this
study were K. D’Loughy, A. Straw, and G. W. Willey, Sr.
We thank the many private citizens and government
employees who have provided information and assistance
over the years.
LITERATURE CITED
Abbott, J. M. 1957. Bald eagle survey: first annual report. Atlantic
Naturalist 12:118–119.
Abbott, J. M. 1963. Bald eagle survey for Chesapeake Bay, 1962. Atlantic
Naturalist 18:22–27.
Abbott, J. M. 1976. Bald eagle nest survey 1976. Atlantic Naturalist 31:
162–163.
Abbott, J. M. 1977. Annual survey report. National Audubon Society,
Washington, D.C., USA.
Abbott, J. M. 1978. Chesapeake Bay bald eagles. Delaware Conservationist
22:3–9.
Anthony, R. G. 2001. Low productivity of bald eagles on Prince of Wales
Island, Southeast Alaska. Journal of Raptor Research 35:1–8.
Anthony, R. G., R. W. Frenzel, F. B. Isaacs, and M. G. Garrett. 1994.
Probable causes of nesting failure in Oregon’s bald eagle population.
Wildlife Society Bulletin 22:576–582.
Bortolotti, G. R. 1989. Factors influencing the growth of bald eagles in
north-central Saskatchewan. Canadian Journal of Zoology 67:606–611.
Brush, G. S. 2001. Forests before and after the colonial encounter. Pages
40–59 in P. D. Curtin, G. S. Brush, and G. W. Fisher, editors.
Discovering the Chesapeake: the history of an ecosystem. Johns Hopkins
University Press, Baltimore, Maryland, USA.
Buehler, D. A. 2000. Bald eagle (Haliaeetus leucocephalus). Account 506 in
A. Poole and F. Gill, editors. The birds of North America. The Academy
of Natural Sciences, Philadelphia, Pennsylvania, and The American
Ornithologists’ Union, Washington, D.C., USA.
Buehler, D. A., J. D. Fraser, J. K. D. Seegar, G. D. Therres, and M. A.
Byrd. 1991a. Survival rates and population dynamics of bald eagles on
Chesapeake Bay. Journal of Wildlife Management 55:608–613.
Buehler, D. A., T. J. Mersman, J. D. Fraser, and J. K. D. Seegar. 1991b.
Effects of human activity on bald eagles in the Chesapeake Bay. Journal
of Wildlife Management 55:282–290.
Byrd, M. A., G. D. Therres, S. N. Wiemeyer, and M. Parkin. 1990.
Chesapeake Bay region bald eagle recovery plan: first revision. U.S.
Department of the Interior Fish and Wildlife Service, Newton Corner,
Massachusetts, USA.
Driscoll, D. E., R. E. Jackman, W. G. Hunt, G. L. Beatty, J. T. Driscoll, R.
L. Glinski, T. A. Gatz, and R. I. Mesta. 1999. Status of nesting bald
eagles in Arizona. Journal of Raptor Research 33:218–226.
Fraser, J. D. 1978. Bald eagle reproductive surveys: accuracy, precision, and
timing. Thesis, University of Minnesota, St. Paul, USA.
Fraser, J. D., S. K. Chandler, D. A. Buehler, and J. K. D. Seegar. 1996. The
decline, recovery and future of the bald eagle population of the
Chesapeake Bay, U.S.A. Pages 181–187 in B. U. Moyberg and R. D.
Chancellor, editors. Eagle studies. World Working Group of Birds of
Prey, Berlin, London, United Kingdom and Paris, France.
Fraser, J. D., L. D. Frenzel, J. E. Mathisen, F. Martin, and M. E. Shough.
1983. Scheduling bald eagle reproductive surveys. Wildlife Society
Bulletin 11:13–16.
Fraser, J. D., F. Martin, L. D. Frenzel, and J. E. Mathisen. 1984.
Accounting for measurement errors in bald eagle reproduction surveys.
Journal of Wildlife Management 48:595–598.
Gray, R. J., J. C. Breeden, J. B. Edwards, M. P. Erkiletian, J. P. Blase
´
Cooke, O. J. Lighthizer, M. J. Forrester, Jr., I. Hand, J. D. Himes, A. R.
McNeal, C. S. Spooner, and W. T. Murphy, Jr. 1988. Population growth
and development in the Chesapeake Bay watershed in the year 2020. U.S.
Environmental Protection Agency, Chesapeake Bay Liaison Office,
Annapolis, Maryland, USA.
Hansen, A. J. 1987. Regulation of bald eagle reproductive rates in Southeast
Alaska. Ecology 68:1387–1392.
Isaacs, F. B., R. G. Anthony, and R. J. Anderson. 1983. Distribution and
productivity of nesting bald eagles in Oregon, 1978–1982. Murrelet 64:
33–38.
Kozie, K. D., and R. K. Anderson. 1991. Productivity, diet, and
environmental contaminants in bald eagles nesting near the Wisconsin
shoreline of Lake Superior. Archives of Environmental Contaminants
and Toxicology 20:41–48.
Kralovec, M. L., R. L. Knight, G. R. Craig, and R. G. McLean. 1992.
Nesting productivity, food habits, and nest sites of bald eagles in
Colorado and southeastern Wyoming. Southwestern Naturalist 37:356–
361.
Markham, A. C. 2004. The influence of salinity on diet composition,
provisioning patterns, and nestling growth in bald eagles in the lower
Chesapeake Bay. Thesis, College of William and Mary, Williamsburg,
Virginia, USA.
Millar, J. G. 1995. Endangered and threatened wildlife and plant; final rule
to reclassify the bald eagle from endangered to threatened in all of the
lower 48 states. Federal Register 60:36000–36010.
Millar, J. G. 1999. Endangered and threatened wildlife and plants;
proposed rule to remove the bald eagle in the lower 48 states from the list
of endangered and threatened wildlife. Federal Register 64:36454–36464.
Millsap, B., T. Breen, E. McConnell, T. Steffer, L. Phillips, N. Douglas,
and S. Taylor. 2004. Comparative fecundity and survival of bald eagles
fledged from suburban and rural natal areas in Florida. Journal of Wildlife
Management 68:1018–1031.
Murdy, E. O., R. S. Birdsong, and J. A. Musick. 1997. Fishes of the
Chesapeake Bay. Smithsonian Institution Press, Washington, D.C.,
USA.
Postupalsky, S. 1974. Raptor reproductive success: some problems with
methods, criteria and terminology. Raptor Research Report 2:21–31.
Sprunt, A., IV. 1963 Continental Bald Eagle Project: progress report No.
III. Proceedings of the National Audubon Society’s Convention, Miami,
Florida, USA.
Sprunt, A., IV., W. B. Robertson, Jr., S. Postupalsky, R. J. Hensel, C. E.
Knoder, and F. J. Ligas. 1973. Comparative productivity of six bald eagle
populations. Transactions of North American Wildlife and Natural
Resource Conference 38:86–106.
Steenhof, K. 1987. Assessing raptor reproductive success and productivity.
Pages 157–170 in B. A. Millsap and K. W. Cline, editors. Raptor
management techniques manual. National Wildlife Federation, Wash-
ington, D.C., USA.
Steenhof, K., and M. N. Kochert. 1982. An evaluation of methods used to
estimate raptor nesting success. Journal of Wildlife Management 46:885–
893.
Steidl, R. J., K. D. Kozie, and R. G. Anthony. 1997. Reproductive success
of bald eagles in interior Alaska. Journal of Wildlife Management 61:
1313–1321.
Swenson, J. E., K. L. Alt, and R. L. Eng. 1986. Ecology of bald eagles in
the Greater Yellowstone Ecosystem. Wildlife Monographs 95.
Therres, G. D., M. A. Byrd, and D. S. Bradshaw. 1993. Effects of
development on nesting bald eagles: case studies from Chesapeake Bay.
Transactions of the North American Wildlife and Natural Resources
Conference 58:62–69.
Therres, G. D., J. S. McKegg, and R. L. Miller. 1988. Maryland’s
Chesapeake Bay Critical Area Program: implications for wildlife.
Transactions of the North American Wildlife and Natural Resources
Conference 53:391–400.
Tyrell, W. B. 1936. Report of bald eagle nest survey of the Chesapeake Bay
region. National Audubon Society, Washington, D.C., USA.
Wallin, D. O. 1982. The influence of environmental conditions on the
breeding behavior of the bald eagle (Haliaeetus leucocephalus) in Virginia.
Thesis, College of William and Mary, Williamsburg, Virginia, USA.
Watson, J. W., D. Stinson, K. R. McAllister, and T. E. Owens. 2002.
Population status of bald eagles breeding in Washington at the end of the
20th century. Journal of Raptor Research 36:161–169.
Watts, B. D. 2006. Evaluation of biological benefits and social
consequences of bald eagle protection standards in Virginia. College of
William and Mary, Center for Conservation Biology Technical Report
CCBTR-06-09, Williamsburg, Virginia, USA.
Watts, B. D., M. A. Byrd, and G. E. Kratimenos. 1994. Production and
implementation of a habitat suitability model for breeding bald eagles in
the lower Chesapeake Bay (phase II: model construction through habitat
Watts et al. Chesapeake Bay Eagles 157
mapping). College of William and Mary Center for Conservation Biology
Technical Report CCBTR-94-06, Williamsburg, Virginia, USA.
Watts, B. D., A. C. Markham, and M. A. Byrd. 2006. Salinity and
population parameters of bald eagles (Haliaeetus leucocephalus) in the
lower Chesapeake Bay. Auk 123:393–404.
Watts, B. D., and D. M. Whalen. 1997. Interactions between eagles and
humans in the James River Bald Eagle Concentration Area. College of
William and Mary, Center for Conservation Biology Technical Report
CCBTR-97-02, Williamsburg, Virginia, USA.
Wiemeyer, S. N., C. M. Bunck, and C. J. Stafford. 1993. Environmental
contaminants in bald eagle eggs—1980–1984—and further interpreta-
tions of relationships to productivity and shell thickness. Archives of
Environmental Contamination and Toxicology 24:213–227.
Wiemeyer, S. N., T. G. Lamont, C. M. Bunck, C. R. Sindelar, F. J.
Gramlich, J. D. Fraser, and M. A. Byrd. 1984. Organochlorine pesticide,
polychlorobiphenyl, and mercury residues in bald eagle eggs—1969–79—
and their relationships to shell thinning and reproduction. Archives of
Environmental Contamination and Toxicology 13:529–549.
Associate Editor: Bechard.
158 The Journal of Wildlife Management 72(1)
... For example, although there were historical declines in Florida (Broley 1947, Cruickshank 1980, resident eagles were neither as heavily impacted nor completely extirpated as in other states (e.g., Oklahoma, Jenkins and Sherrod 2005;California, Sorenson et al. 2017). In addition, the rate of population growth we observed (5.5%) was less than increases reported for the Chesapeake Bay (9.4%, Watts et al. 2008), Texas (13%, Saalfeld et al. 2009), Louisiana (11.1%, Smith et al. 2016, and likely Kansas (Winder and Watkins 2020). Mean productivity in Florida was consistently .1 fledglings per occupied territory, in alignment with findings from other state populations (Jenkins and Sherrod 2005, Stinson et al. 2007, Watts et al. 2008, Saalfeld et al. 2009, Smith et al. 2016. ...
... In addition, the rate of population growth we observed (5.5%) was less than increases reported for the Chesapeake Bay (9.4%, Watts et al. 2008), Texas (13%, Saalfeld et al. 2009), Louisiana (11.1%, Smith et al. 2016, and likely Kansas (Winder and Watkins 2020). Mean productivity in Florida was consistently .1 fledglings per occupied territory, in alignment with findings from other state populations (Jenkins and Sherrod 2005, Stinson et al. 2007, Watts et al. 2008, Saalfeld et al. 2009, Smith et al. 2016. This exceeded both the minimum rate cited for population maintenance (0.7, Sprunt et al. 1973) and the recovery goal established by the Southeastern States Bald Eagle Recovery Plan (0.9; USFWS 1989). ...
Article
The range-wide recovery of Bald Eagles (Haliaeetus leucocephalus) is one of the great North American conservation successes, with the Bald Eagle population in Florida contributing substantially to this recovery. Florida has one of the densest concentrations of nesting Bald Eagles in the lower 48 states and sustained a population monitoring program that spanned 45 yr. We used nest monitoring data from 1972–2017 to quantify changes in the size, extent, and productivity of the breeding Bald Eagle population in Florida. We documented an increase in the number of occupied Bald Eagle territories from 88 in 1973 to an estimated 1565 in 2017, with nests recorded in 64 of Florida's 67 counties by the end of the monitoring efforts. Mean annual growth rate in the number of occupied eagle territories in Florida was 5.5 ± 1.1% (SE). High reproductive rates, exemplified by a mean productivity of 1.13 ± 0.02 fledglings per occupied nest, a mean brood size of 1.54 ± 0.01 fledglings per successful nest, and the production of nearly 40,000 fledglings over a 45-yr period, translated into substantial gains for the state and southeastern US Bald Eagle population. Eagles have established a large, spatially expansive, and productive breeding population in Florida, one that exceeded the conservation objectives established when the species was state-delisted in 2008. These data provided key insights into the breeding ecology, recovery, and long-term stability of Bald Eagles in Florida. Given the predicted increase in the human population and landscape modification anticipated in the coming years, the conservation of the eagle population within Florida will require adaptive management strategies.
... Species such as the redtailed hawk (Buteo jamaicensis) and Cooper's hawk (Accipiter cooperii) have become more common, likely benefiting from increased prey availability in reforested areas and adaptation to suburban/urban environments (Stout and Rosenfield 2010). Governmental bans on the pesticide DDT (dichloro-diphenyltrichloroethane), which was widely used in agricultural settings until the 1970s and caused eggshells to become brittle in birds, has led to significant recovery in some raptor species, especially Bald Eagles (Haliaeetus leucocephalus; Watts, Therres, and Byrd 2008). Last, many of the species increasing between both seasons are short-distance migrants or resident species. ...
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Aim Seasonality governs species composition at a given place and time. However, the effects of climate and land‐use change can vary by season, altering species composition. These changes can lead to a loss of distinct seasonal community composition, representing a novel form of biotic homogenisation. We ask if breeding and winter bird communities are becoming more similar over time. If so, is homogenisation occurring more rapidly in winter than in the breeding season, and has the presence of individual species changed between seasons? Location Northeastern United States. Time Period 1989–2019. Major Taxa Studied Two hundred thirty‐eight bird species. Methods We use data from The National Audubon Society's Christmas Bird Count and the North American Breeding Bird Survey to test if winter and breeding bird communities have become more similar (homogenised). We evaluate this change using the Sørensen dissimilarity index, and its components of turnover (species replacement) and nestedness (a subset of a more species rich community) and describe the mechanism in which the seasonal winter and breeding bird communities are changing. Results We found that winter and breeding bird communities are homogenising, driven by significant decrease in turnover and a marginal decrease nestedness. When viewing breeding and wintering communities separately, we observe different trends. Breeding communities are becoming more unique with decreasing turnover and nestedness. Winter communities are becoming more similar to each other, with decreasing turnover and nestedness. More breeding species are declining and species that are typically found in the winter and year‐round residents are the main contributors to the homogenisation between seasons. Main Conclusions We show for the first time homogenisation between winter and breeding bird communities over time across the northeastern United States. This insight into how individual species are faring between seasons, and how they impact community structure, can be used when implementing conservation measures for maintaining ecological functioning and integrity.
... To identify and mitigate threats to raptor populations, research on an individual species throughout its geographic distribution, along with communication and collaboration among scientists can lead to successful conservation measures. For example, dedicated research and collaboration have led to significant progress toward long-term population persistence of the Peregrine Falcon (Falco peregrinus), Bald Eagle (Haliaeetus leucocephalus), and California Condor (Gymnogyps californianus) in North America (Watts et al. 2008, 2015, Walters et al. 2010, Mauritius Kestrel (Falco punctatus) on the island of Mauritius in the western Indian Ocean (Jones et al. 1994), and the Golden Eagle (Aquila chrysaetos, Fernández-Gil et al. 2022) and Saker Falcon (Falco cherrug, Lazarova et al. 2021) in Europe. ...
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Because information availability and management are essential components of wildlife conservation, we sought to compile literature published since 1900 on the caracaras, a group of nine extant species, eight of which occur only in Central America and South America. Our findings revealed that the number of sources and therefore, the amount and types of information available varied considerably among the caracara species and among countries where these raptors occur. Most sources represented studies conducted in Argentina, the United States, Brazil, and Chile, and many focused on the more common species, for example, the Crested Caracara (Caracara plancus) and the Chimango Caracara (Milvago chimango). Most sources published in the early 20th century focused on breeding and feeding ecology and natural history. Since the 1960s, the number of studies published per decade has increased, and since the 1990s, more studies have addressed a broader range of topics including behavioral ecology, demography, infectious agents, parasites, contaminants, biomedicine, and taxonomic relatedness among the caracara species and other falcons. Aside from the Striated Caracara (Phalcoboenus australis), which recently has been the subject of intensive research, other species in the genus Phalcoboenus (the Mountain Caracara [P. megalopterus]; the White-throated Caracara [P. albogularis]; and the Carunculated Caracara, [P. carunculatus]) remain little known, as do the two forest-dwelling caracaras, the Black Caracara (Daptrius ater) and the Red-throated Caracara (Ibycter americanus). Knowledge gaps exist for all the caracaras; research is especially needed on subjects outside typically studied topics such as breeding and feeding ecology. Also important to expanding knowledge of this group will be collaboration with researchers studying other avian scavengers such as condors and vultures, focusing on common threats, and coordination among researchers in countries inhabited by multiple caracara species. EVALUANDO EL CONOCIMIENTO SOBRE LOS CARACARAS: COMPILANDO INFORMACIÓN, IDENTIFICANDO VACÍOS DE CONOCIMIENTO Y RECOMENDACIONES PARA INVESTIGACIONES FUTURAS RESUMEN.-Contar con información y poder implementar medidas de gestión es esencial para la conservación de la fauna silvestre. Consecuentemente, realizamos una revisión exhaustiva de la literatura existente para las nueve especies reconocidas de caracaras, sobre las que existe información limitada cuando se compara con rapaces de Norte América, Europa y otras regiones fuera de la región Neotropical. Nuestro análisis identificó, en base al número y tipos de fuente, que la cantidad de información existente sobre este grupo varió en función de la especie y del país donde habitan. La mayoría de las publicaciones se originaron en estudios realizados en Argentina, Estados Unidos, Brasil y 1 Chile y sobre las especies más comunes, por ejemplo, Caracara plancus y Milvago chimango. A partir de la década de 1960 se observó un aumento en el número de publicaciones; previamente éstas estaban focali-zadas en la historia natural y la ecología reproductiva y trófica de estas especies. A partir de la década de 1990, los trabajos publicados sobre este grupo ampliaron el rango de temas estudiados, incluyendo ecología comportamental, demografía, agentes infecciosos y parasitarios, contaminantes, biomedicina, e incluso estudios taxonómicos dedicados a entender mejor tanto las relaciones entre las distintas especies de caracaras entre sí como su relación con los halcones. Excepto para Phalcoboenus australis, quien recien-temente ha sido objeto de investigación intensiva, otras especies en el género Phalcoboenus (P. megalopteris, P. albogularis y P. carunculatus) siguen siendo prácticamente desconocidas, al igual que las dos especies de caracaras selváticos, Daptrius ater e Ibycter americanus. Se necesita un mayor número de estudios sobre todas las especies de caracaras que incluyan otros temas más allá de la ecología reproductiva y trófica. La colaboración con investigadores que trabajan con otras especies de rapaces carroñeras, como cóndores y gallinazos, es esencial. Una mayor integración y coordinación de los esfuerzos permitirá identificar y reducir las amenazas comunes para estos grupos, sobre todo en aquellos países que cuentan con varias especies de caracaras.
... Likewise, Bald Eagles may also respond negatively to structures themselves or habitat modifications, because, even during seasons with low human activity, they avoided developed areas (Buehler et al. 1991). In the long term, the Bald Eagle's capacity to cope with human activity and the ability to manage appropriate breeding habitats will determine the size and stability of breeding populations (Watts et al. 2008). ...
... For birds of North America, reference conditions beginning in the latter part of the 20th century coincide with the advent of federal environmental protections (Grier, 1982;Scott et al., 2005;Watts et al., 2008) and may thus mask important population dynamics resulting from anthropogenic drivers occurring earlier on, including land conversion (Stanton et al., 2018), hunting (Bucher, 1992), and pesticide use (Mineau & Whiteside, 2013). ...
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Understanding population changes across long time scales and at fine spatiotemporal resolutions is important for confronting a broad suite of conservation challenges. However, this task is hampered by a lack of quality long-term census data for multiple species collected across large geographic regions. Here, we used century-long (1919-2018) data from the Audubon Christmas Bird Count (CBC) survey to assess population changes in over 300 avian species in North America and evaluate their temporal non-stationarity. To estimate population sizes across the entire century, we employed a Bayesian hierarchical model that accounts for species detection probabilities, variable sampling effort, and missing data. We evaluated population trends using generalized additive models (GAMs) and assessed temporal non-stationarity in the rate of population change by extracting the first derivatives from the fitted GAM functions. We then summarized the population dynamics across species, space, and time using a non-parametric clustering algorithm that categorized individual population trends into four distinct trend clusters. We found that species varied widely in their population trajectories, with over 90% of species showing a considerable degree of spatial and/or temporal non-stationarity, and many showing strong shifts in the direction and magnitude of population trends throughout the past century. Species were roughly equally distributed across the four clusters of population trajectories, although grassland, forest, and desert specialists more commonly showed declining trends. Interestingly, for many species, region-wide population trends often differed from those observed at individual sites, suggesting that conservation decisions need to be tailored to fine spatial scales. Together, our results highlight the importance of considering spatial and temporal non-stationarity when assessing long-term population changes. More generally, we demonstrate the promise of novel statistical techniques for improving the utility and extending the temporal scope of existing citizen science datasets.
... Several recent papers suggest general strategies for increasing species resilience, including increasing connectivity between habitats and populations, broadening the spatial distribution of subpopulations, increasing genetic or life history diversity, and reducing climate change effects on habitats Davies, 2010;Dunwiddie et al., 2009;Waldman et al., 2016). There is also evidence that restoring habitat capacity (e.g., increasing habitat area) may be more important for recovery of some species (Kautz et al., 2006;Kerr & Deguise, 2004;Walters, Copeland, & Venditti, 2013), whereas increasing productivity (reproductive success) may be more important for others (Grier, 1982;Watts et al., 2008). While each of these strategies has been considered individually, there have been few attempts to compare the likely effectiveness of different strategies for increasing resilience of species to climate change, nor of the mechanisms that may increase resilience (Battin et al., 2007;Justice et al., 2017). ...
Article
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A pressing question for managing recovery of depressed or declining species is: Can habitat restoration increase resilience to climate change? We addressed this question for salmon populations with varying life histories, where resilience is defined as maintaining or increasing population size despite climate change effects. Previous studies indicate that several interrelated mechanisms may influence salmon resilience to climate change, including improving either habitat capacity or productivity, and ameliorating climate change effects on flood flow, low flow, or stream temperature. Using the Habitat Assessment and Restoration Planning (HARP) model, we first examined the relative importance of each mechanism for increasing salmon population resilience by comparing projected salmon spawner abundance for seven individual restoration action types under current and projected mid‐ and late‐century climates. We found that restoring habitats with the greatest restoration potential most increased resilience for all species, but the most beneficial restoration actions varied among species. Increasing habitat capacity and productivity both contributed to resilience, and ameliorating climate change effects was important in a few subbasins where the restoration opportunity was widespread. Cool‐water climate refuges contributed to resilience of some subpopulations by reducing late‐century declines in spawner abundance even without restoration. We also modeled more complex habitat restoration strategies comprised of several restoration action types at varying restoration intensities and found that the restoration action types and level of restoration effort needed to increase resilience varied among species. Less vulnerable species such as coho salmon responded well to four restoration actions (floodplain reconnection, wood augmentation, increased shade, and increased beaver ponds) applied at low restoration intensity and over a large area. More vulnerable species such as spring Chinook responded to fewer action types (floodplain reconnection, wood augmentation, and increased shade), but at much higher intensity and over a much smaller area. The analysis also identified important locations for each restoration action type for each species, which helps focus habitat restoration effort on areas that are likely to provide the largest increases in resilience.
... For example, Bald Eagle populations have more than doubled. Other studies have demonstrated drastic increases in Bald Eagle populations (Farmer et al., 2008;McClure et al., 2021b;Watts et al., 2008) likely due to a continuing rebound from the DDT era (Grier, 1982;Postupalsky, 1978;Smith et al., 2016). Our results also support the assertion that Cooper's Hawk populations are generally increasing across the USA and Canada Rosenberg et al., 2019;Smallwood et al., 2009). ...
Article
To effectively maximize the conservation value of management plans intended to capture ecosystem-wide health, it is essential to obtain an understanding of emergent patterns in dietary dynamics spanning many species. Chesapeake Bay, USA, is a critical ecosystem used annually by a diverse assortment of waterbird species, including several of conservation concern. However, the ecosystem is threatened by many ecological pressures driven largely by the dense human population of the surrounding region. These issues necessitate proactive monitoring and management efforts to track the health of ecosystems like the Chesapeake Bay. Such monitoring efforts of population dynamics require adequate data on the connections between trophic levels to understand how changes to the forage base might influence higher trophic levels, such as these diverse avian predators. However, we have historically lacked standardized quantitative data drawing these connections at the community level, as well as the relative importance of these taxa in the diet of such predators. We collated existing quantitative data on avian dietary composition to construct a database on the diets of 58 waterbird species that make use of the Chesapeake Bay. From this database, we quantified the relative importance of forage taxa to the diet of each waterbird species. Such data can enable managers to develop a comprehensive suite of forage taxa indicators whose abundance and distributions can be monitored as a proxy for ecosystem health. It is our goal that this database be harnessed as a tool to enable conservation practitioners to prioritize indicator taxa for monitoring purposes, contributing towards conservation plans that best address the health of the ecosystem at large.
Article
The Chesapeake Bay, along the mid-Atlantic coast of North America, is the largest estuary in the United States and provides critical habitat for wildlife. In contrast to point and non-point source release of pesticides, metals, and industrial, personal care and household use chemicals on biota in this watershed, there has only been scant attention to potential exposure and effects of algal toxins on wildlife in the Chesapeake Bay region. As background, we first review the scientific literature on algal toxins and harmful algal bloom (HAB) events in various regions of the world that principally affected birds, and to a lesser degree other wildlife. To examine the situation for the Chesapeake, we compiled information from government reports and databases summarizing wildlife mortality events for 2000 through 2020 that were associated with potentially toxic algae and HAB events. Summary findings indicate that there have been few wildlife mortality incidents definitively linked to HABs, other mortality events that were suspected to be related to HABs, and more instances in which HABs may have indirectly contributed to or occurred coincident with wildlife mortality. The dominant toxins found in the Chesapeake Bay drainage that could potentially affect wildlife are microcystins, with concentrations in water approaching or exceeding human-based thresholds for ceasing recreational use and drinking water at a number of locations. As an increasing trend in HAB events in the U.S. and in the Chesapeake Bay have been reported, additional information on HAB toxin exposure routes, comparative sensitivity among species, consequences of sublethal exposure, and better diagnostic and risk criteria would greatly assist in predicting algal toxin hazard and risks to wildlife.
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From 1980-98 the population of Bald Eagles (Haliaeetus leucocephalus) nesting in Washington increased (P < 0.001) at an exponential, annual rate of 10% as adult eagles reoccupied habitat vacated during the period of widespread persecution and DDT use. Further indications of population health were linear increases in the rates of nest occupancy, productivity, and nest success. Productivity and nest success of eagles affected by contaminants along Hood Canal and the Washington side of the Columbia River estuary also increased during the study period but remained below statewide averages. By 1998, the population was widely distributed, with 89% of pairs nesting west of the Cascade crest, and 11% east of the crest. There were indications that the population stabilized from 1993-98, when statewide occupancy rates decreased (P = 0.040), and productivity and nest success stabilized. Modeling predicts that a statewide population of 733 breeding pairs at carrying capacity would, after 25 yr, provide an equilibrium population of 4913 eagles. Stability of the statewide population of Bald Eagles seems to be less dependent on productivity rates than on adequate numbers of replacement adults, as maintained through high survival.
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Only 55 of 1117 locations of radio-tagged Haliaeetus leucocephalus (4.9%) occurred in the developed land-cover type ≥4 buildings/4 ha), although 18.2% of potential eagle habitat was developed. Eagle use of the shoreline was inversely related to building density and directly related to the development set-back distance. Few eagles used shoreline segments with boats or pedestrians nearby. Only 360 of 2532 segments (14.2%) had neither human activity nor shoreline development. Eagle flush distances because of approaching boats were greater in winter than in summer (mean 264.9 vs. 175.5 m, respectively), but were similar for adult and immature eagles (203.7 vs. 228.6 m, respectively). Of 2472 km of shoreline on the N Chesapeake, 894 km (36.2%) appears to be too developed to be suitable for eagle use, and an additional 996 km (40.3%) had buildings within 500 m, thereby reducing eagle use. The projected increase in developed land in Maryland (74%) and Virginia (80%) from 1878 to 2020 is likely to determine the future of the bald eagle population in this area. (See also 91L/12673). -from Authors
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Aimed to determine 1) the frequency and causes of error in aerial surveys at different stages of the breeding season of Haliaeetus leucocephalus on the Chippewa National Forest, and 2) the aerial survey schedule that would provide the most accurate estimates of nesting parameters of the bald eagle population. -from Authors
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The Chesapeake Bay may once have provided habitat for as many as three thousand pairs of breeding bald eagles and for thousands of subadult and migrant birds. The population has declined dramatically over the past three centuries due to habitat destruction, persecution, and contamination by DDT and other chemicals, reaching a low of 80-90 breeding pairs in 1970. After DDT was banned in 1972, the population began to increase. In 1989, 185 pairs of eagles nested in Maryland and Virginia. Eagles require large trees for nesting, roosting, and perching. These trees must be in areas with limited human activity. Bald eagles are opportunistic predator-scavengers, consuming many different prey species. They take fish when they are available, but shift to waterflow and mammals when fish are scarce. The long-term survival of the bald eagle on Chesapeake Bay will be determined by the management of shoreline habitat. The very rapid rate of shoreline development, if unchecked, will eliminate most large undistributed forest blocks in the next 50-100 years and will lead to a decline and perhaps extirpation of the species from the Chesapeake Bay area. This can be avoided if a series of shoreline refuges is created. Adequate fish and waterfowl populations also will be required to sustain the species in the future.
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Developed a probabilistic method of distinguishing real changes in Haliaeetus leucocephalus reproduction on the Chippewa National Forest from apparent changes caused by errors in the annual two-flight survey. -from Authors