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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)