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The Virginia Bald Eagle Survey: A History

Page 5'
Center for Conservation Biology
College of William and Mary and Virginia Commonwealth University
Williamsburg, VA 23187-8795, USA
The Virginia Bald Eagle Survey is a national treasure.
The survey has become one of the most significant serial
data sets in the world. Over the past 55 years, the survey has
documented biocide-induced reproductive suppression,
the resulting population low, and a dramatic recovery
in both reproductive rates and the overall population
following the ban of DDT and like compounds. The survey
itself has become one of the most effective tools in the effort
to recover the eagle population in Virginia, allowing for the
enforcement of wildlife laws and providing information
on the effectiveness of management actions. More than
population information alone, the effort has produced a
wealth of ecological information on a population recovering
within an increasingly human-dominated landscape. It has
become one of the best records of arguably the greatest
conservation achievement in our nation's history. My
objective here is to provide a brief history of the survey
effort and some of the events that shaped its development.
Tyrrell Survey
In the spring of 1935, during a time when bald eagles
were persecuted throughout their range, a bill was
introduced in Congress to protect the national symbol
from extinction. The bill passed the Senate, but failed in
the House of Representatives. [A modification of this bill
became the Bald and Golden Eagle Act of 1940 (16 U.S.C.
668-668d; 54 Stat. 250).] During the breeding season of 1934,
W. Bryant Tyrrell and other members of the Natural History
Society of Maryland made regular observations of an eagle
nest along the Magothy River south of Baltimore, including
prey use and chick development through the period of
fledging. Photographs of the chicks appeared in the New
York Times and were brought to the attention of Warren F.
Eaton. Eaton was working on the status of hawks and owls
and their economic importance. Eaton contacted Tyrrell
about the possibility of a survey of eagles throughout the
Chesapeake Bay region and an investigation of food habits.
Understanding the gravity of the situation and the
need to collect information to support the Senate bill, Tyrrell
wrote a letter to Professor R. V. Truitt of the University of
Maryland inquiring about the potential for funding from
the University or the State to support such a survey. Truitt
contacted the National Audubon Society and in January
of 1936 the president of that Society, John H. Baker, met
with Warren Eaton and Bryant Tyrrell in New York City to
lay out a plan and to acquire associated funding to survey
nesting eagles throughout the Bay region, including New
Jersey, Delaware, Maryland, and Virginia.
Tyrrell initiated the nest survey in February of 1936
(Tyrrell 1936). He began by contacting the community of
ornithologists, oologists, game wardens, and other people
who were most likely to know of nest locations. Harold H.
Bailey provided him with a map of 54 nests in Virginia.
Edward J. Court, a prominent egg collector in the region,
claimed to know of 90 nest locations, but provided Tyrrell
with only eight that could not be climbed. Tyrrell used these
eight locations as a basis for the survey, but when entering
a new community he would also visit the country store and
local landowners to take advantage of local knowledge
about breeding pairs, and thus accumulated additional
nest sites for the survey.
Although the survey was ground-based and covered
only a portion of the region, it became the benchmark
against which future efforts would be compared (e.g.,
Abbott, 1963; Byrd et al., 1990; Watts et al., 2008). This is
true because it was the only major effort to quantify eagle
numbers and productivity prior to the DDT era. In Virginia,
the survey included the Potomac River to its mouth, a small
portion of the Rappahannock River, approximately 20 miles
of the James River east of Richmond, and the coastal area
from Pungo through Back Bay. Tyrrell surveyed 19 nests,
16 of which were occupied in 1936. Fifteen of these nests
successfully produced 33 chicks.
The efforts of Tyrrell have provided the conservation
community with more than a population survey. His report
to the National Audubon Society, notes, and nest logs
provide an account of eagle-human interactions during a
critical time before both
passage of the Bald and Golden
Eagle Act and the DDT era, a time during which eagles
were under considerable pressure from various sectors
of society (e.g., loggers gave eagles no consideration and
numerous nest trees were lost annually to forest clearing;
many fur trappers, farmers, and waterfowl hunters shot
eagles on sight; collectors staked out nests in order to take
adult pairs and eggs for sale on the open market).
Modern Survey
Despite the fact that he never surveyed eagles within
the Chesapeake Bay, Charles
Broley and his work on
Florida eagles ignited a national conservation movement
and indirectly led to the establishment of the Chesapeake
Bay Bald Eagle Survey. Broley, a retired bank manager from
Winnipeg, Canada, spent the winter months in Tampa,
Florida. He became increasingly concerned about habitat
loss, shooting, and egg collecting in western Florida that
he believed was causing eagle declines. At the age of 60, he
initiated a banding program in 1939 and banded more than
1,200 eaglets over the following 20 years. Broley's seminal
work not only documented new aspects of eagle ecology
(Broley 1947), but also provided one of the most complete
records of progressive nest failures during the early years
of the DDT era. In an area where he once banded more than
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Vol. 81
150 chicks in a single year, by 1958 Broley could only locate
a single chick to band. His energy and relentless advocacy
on behalf of eagle conservation spawned efforts across the
species range. His belief that the Chesapeake Bay could
serve as a stronghold for the species in the East led to the
Bay becoming one of the first focal monitoring locations.
In 1955, a committee was established within the
Audubon Naturalist Society to collect data on the status of
bald eagles within the Chesapeake Bay region (Abbott 1957).
Jackson Miles Abbott was a member of that committee and
would lead the survey effort for the next 20 years. Abbott, a
military engineer, accomplished naturalist, artist, lecturer,
and writer transformed the effort from a volunteer project
to a formal survey. Many of the ecological discoveries
made in the survey's early years led to the development of
effective aerial monitoring. Abbott's detailed field notes and
published papers provide a complete accounting of efforts
and observations during a critical period of the survey's
development. The survey would not have survived and
prospered without his leadership and dedication.
Between 1956 and 1962, the survey progressed from
a volunteer-based ground survey to a more effective
aerial survey (Abbott 1967). The survey was first
conceived as a volunteer effort. The committee executed
an outreach campaign to recruit observers that included
announcements in the Washington Post. In the first year,
nine observers provided nest locations and observations.
Despite a considerable outreach campaign, the committee
was unable to engage a large enough pool of qualified
observers to cover known nesting sites or to complete
follow-up productivity observations. By 1960 the effort had
collected information on 68 nest sites, but information on
productivity was limited. During the first 4 years, Abbott
was never able to exceed 20% coverage of known nests
by volunteers, due to the small pool of observers and the
remoteness of many nests. During these initial five years
it became increasingly evident to Abbott that a ground
effort would not be adequate to meet survey objectives.
In the spring of 1959, Abbott had the first opportunity to
do a limited flight for eagles in an H-23 army helicopter
and realized that aerial surveys were the best option for
monitoring nests. During the 1960 National Audubon
Society convention in New York City, Alexander Sprunt
IV announced a continental effort by the Society to assess
bald eagle populations. The effort focused on a mid-winter
survey and breeding surveys within selected geographic
areas of importance. The Chesapeake Bay Survey joined
this effort, and in 1962 Abbott conducted the first aerial
survey of the Bay with an assessment of productivity
(Abbott 1963). The army provided helicopter support
along the Potomac and the United States Fish and Wildlife
Service provided survey planes for the remaining areas.
In 1963, Frederick R. Scott III joined Abbott in
conducting the aerial survey and the team flew the Bay for
eagles through 1976. Often considered the dean of Virginia
birdwatchers, Scott had an encyclopedic knowledge of
bird populations, was the editor of The Raven for 27 years,
and was one of the region's staunchest conservationists.
During most years, Abbott flew the upper Bay from the
Potomac River north and Scott flew the lower Bay from
the Rappahannock River south. Through the 1960s and
1970s, Abbott and Scott served as witnesses to a stable but
unsettled eagle population with low productivity and high
abandonment rates.
The year 1977 was a transition year for the bald
eagle survey and for eagle conservation within the
Chesapeake Bay. In January of 1977, the Chesapeake
Region Eagle Group was established with representatives
from the Fish and Wildlife Service, Maryland Wildlife
Administration, Virginia Game Commission, the National
Wildlife Federation, the Audubon Naturalist Society, the
Maryland Ornithological Society, and the Virginia Society
of Ornithology. Very close to this time period, the Fish and
Wildlife Service, under the authority of the Endangered
Species Act, appointed a Chesapeake Bay Bald Eagle
Recovery Team to develop a recovery plan and to oversee
monitoring and recovery efforts. During that same year, the
state wildlife agencies assumed responsibility
for the nest
survey. In Virginia, Mitchell A. Byrd, professor of biology at
the College of William and Mary and a true pioneer of bird
conservation, conducted the survey on behalf of the state
agency, and he remained committed to the survey for the
next 34 years. In 1991, Bryan D. Watts joined the Virginia
survey and the two monitored the population together for
the next 20 years.
Following the federal listing of bald eagles in 1967
under the Endangered Species Protection Act of 1966
(16 U.S.C. 668aa-668cc) and, subsequently, under The
Endangered Species Act of 1973 (16 U.S.C. 1531 et seq.),
efforts were mounted throughout the species range
and there was a movement toward more standardized
monitoring programs. The Virginia survey transitioned
to a standard two-flight approach, consisting of one flight
in March to locate new nests and determine the status of
known nests, and a second flight in late April and May
to check active nests for productivity. The survey also
became more systematic in its coverage of the Coastal Plain
including Chesapeake Bay tributaries to the fall line, the
Eastern Shore, and lower Tidewater including Back Bay and
the North Landing River. Mapping of nests became more
standardized, using 7.5 minute topographic quadrangles
to provide the resolution needed to enforce regulations of
The Endangered Species Act.
As bald eagle populations continued their remarkable
recovery throughout the late 1990s, wildlife agencies across
the species range began to divert resources away from
eagle monitoring to more pressing priorities. Beginning
in 2000, financial responsibility for the Virginia survey has
been increasingly assumed by the Center for Conservation
Biology, a research and conservation organization founded
in 1992 by Bryan Watts and Mitchell Byrd. The Center is
shared between the College of William and Mary and the
Virginia Commonwealth University and is committed to
long-term species conservation. This survey has continued
to document eagle population growth, productivity and
distribution to the present. The 2010 survey checked more
than 900 nests and monitored 684 occupied territories
(Watts and Byrd, 2010). Throughout the years, the survey
has conducted more than 22,000 nest checks, including
more than 13,000 since the year 2000.
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The Virginia Bald Eagle Survey has truly been a
community effort with contributions from dozens of eagle
biologists, environmental activists, bird watchers, and
concerned citizens all coming together around a common
goal. Funding for the Virginia Survey has been provided
by the Virginia Department of Game and Inland Fisheries,
U.S. Fish and Wildlife Service, U.S. Department of Defense,
Audubon Naturalist Society, National Audubon Society,
Virginia Society of Ornithology, and the Center for
Conservation Biology.
Literature Cited
Abbott, J. M. 1957. Bald Eagle survey: first annual report.
Atlantic Naturalist
Abbott, J. M. 1963. Bald eagle survey for Chesapeake Bay,
Atlantic Naturalist
Abbott, J. M. 1967. The Chesapeake Bay eagles: Summary
Report - 1936; 1955-1965.
Atlantic Naturalist
Broley, C. L. 1947. Migration and nesting of Florida Bald
Wilson Bulletin
Byrd, M. A., Therres, G. D, Wiemeyer, S. N., 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, MA. 49 pp.
Tyrrell, W. B. 1936. Unpublished report of bald eagle
nest survey of the Chesapeake Bay region. National
Audubon Society, Washington, D.C. 30 pp.
Watts, B. D. and Byrd, M. A. 2010. Virginia bald eagle
nest and productivity survey: Year 2010 report.
Center for Conservation Biology Technical Report
Series, CCBTR-10-09. College of William and Mary,
Williamsburg, VA. 40 pp.
Watts, B. D., G. D. Therres, G. D., and Byrd, M. A. 2008.
Recovery of the Chesapeake Bay bald eagle nesting
Journal of Wildlife Management
... The entire study area has been surveyed systematically for nesting bald eagles for 50 years (1962-2011) with a minimum of 2 flights per season (Abbott 1963, Watts 2010. A survey flight is conducted between late February and mid-March to locate nesting territories. ...
... The cost structure for management scenarios is sensitive to the underlying forces that drive shifts in activity status for both nests and nest trees. Turnover and loss rates of nests are high within the study area (Watts andDuerr 2010). Clearly these parameters vary across the wide breeding range of this species, but it is not clear where the Chesapeake Bay fits within this range. ...
Full-text available
For over 30 years, bald eagle (Haliaeetus leucocephalus) nests and nest trees have been managed using a combination of spatial buffers and time-of-year restrictions. Most management standards include the protection of nests currently in use as well as alternate nests and trees that have lost nests. Protection is extended to alternate nest structures under the assumption that they provide value to the breeding population. However, the notion that these structures hold enough residual value to warrant the cost of their protection has not been fully explored. I used nest histories (n > 2,250) from a long-term (1962–2011) dataset collected in the lower Chesapeake Bay to evaluate the relationship between management costs and residual value across the range of management scenarios currently in use. I used a joint, multistrata, live-recapture/dead-recovery model in Program MARK to estimate probabilities of annual survival for active and alternate nests and transition probabilities between active and alternate nests. My primary objective was to assess the residual biological value of alternate nests and trees relative to the management costs required to protect them. I estimated the per capita management costs and the residual value of alternate nests and trees. Survival rates were 0.902 ± 0.007 (mean ± SE) and 0.703 ± 0.017 for active and alternate nests, respectively. Of 1,163 alternate nests, 352 (30.3%) were determined to be re-used within 5 years. However, the likelihood of re-use declined with time. Most re-used nests were re-used in the first year (76.4%), with virtually all (98.6%) being re-used in the first 3 years. Only 9.9% (168 of 1,699) of trees that had lost nests were re-used within the first 10 years. Nests were rebuilt in 32% (equating to 3.1% re-use) of re-used trees in the first year and in 71.4% of these trees in the first 3 years. Implementation of current national management guidelines resulted in 2.35 nest equivalents of management cost for each active nest in the population. The residual value and cost functions diverged over time such that the return on social investment diminishes over the management periods. The cost-to-benefit relationship is particularly poor when the protection of alternate nests is extended beyond 3 years and when protection is extended to trees that have lost nests. © 2015 The Wildlife Society.
... The Chesapeake Bay is an important recovery unit for bald eagles and monitoring has been a component of both the Bay-wide ) and Virginia (Watts 2005) conservation plans. The breeding population has been surveyed annually for more than 50 years beginning with a ground survey in 1957 and the establishment of an aerial survey in 1962 (Abbott 1963, Watts 2010. The aerial survey has employed a standard two-flight approach (Fraser et al. 1983) to track the entire population within the tidal reach of the Bay and to estimate reproductive rates. ...
... Because of the annual variation in egg lay date, the exact timing of the influx of fledgling eagles into the population may be difficult to predict in any given year (Watts et al. 2007). Consequently, monitoring of the nesting cycle, such as that currently being conducted in the Chesapeake Bay by The Center for Conservation Biology (Watts 2010) and providing a mechanism to relay that information to airfield managers, would help managers plan for increased monitoring and deterrent activities. Such information could contribute to decreased BASH brought on by this influx of young, inexperienced eagles. ...
Bald eagle (Haliaeetus leucocephalus) aircraft strikes have increased since 1998 because their populations have recovered to near historical sizes. Their attraction to airfields and their large body size makes them a danger to aircraft and therefore important to airfield managers. However, bald eagle management is complicated by their special protected status and the place they hold in the eyes of the public. To help airfield managers plan monitoring efforts and make informed management decisions, we studied the movements of 32 bald eagles telemetered as nestlings in the Chesapeake Bay, Virginia, USA, 2013–2018. Managers often need to know when fledged eagles are most likely to move enough to encounter airfields near nests. As fledglings aged, they moved progressively farther from the nest and spent more time away from the nest. Twenty-eight days after fledging, eagles spent most of the day (81 ± 10% [95% CI]) near the nest (<500 m) and only 7 ± 7% of the daytime away from the nest (>1 km). By day 55 fledglings ventured beyond 2.5 km from the nest and spent 32 ± 15% the day >1 km away from their nest. Distances moved, however, were influenced by proximity of the nest to water, the salinity of that water, and human population density. Eagles left their natal nests and generally migrated out of the Chesapeake Bay 60.5 ± 7.7 days (4 Aug) after fledging and returned to the Chesapeake Bay approximately 220 days later (Mar–Apr). Eighty-four percent (27 of 32) of the eagles that we tracked encountered 164 airfields across the east coast with 91% of those airfields located within 10 km of the Chesapeake Bay. Encounters with airfields outside the Chesapeake Bay occurred mainly during the first 1.5 years of life, peaking in late fall and early spring. We recorded eagles on Chesapeake Bay airfields during each year, but encounters peaked in April of the first year of the bird's life. April coincides with the height of reported strikes of eagles by aircraft in the region. Our results suggest that eagles fledging from the Chesapeake Bay are an issue for airports near the Chesapeake Bay and for airports across the east coast. Given the continued growth of the population, this issue is likely to continue and grow in significance.
... The Virginia bald eagle population is part of the broader breeding population within the Chesapeake Bay region (Watts 2005). The population has been systematically monitored from the air since 1962 (Watts 2010) and reached a low of 26 pairs in the early 1970s (Abbott 1975). The species was proposed for endangered status within Virginia during both 1978 and 1989 (Byrd 1979b(Byrd , 1991b due to the reduced population status, contaminant-induced reproductive suppression and ongoing habitat loss. ...
Full-text available
Virginia supports a diverse community of breeding birds that has been the focus of investigation for more than 400 years. The avifauna reflects the latitudinal position of the state and the fact that the border extends from the Atlantic Ocean to the Appalachian Mountains. A total of 224 species have been recorded breeding in Virginia, 214 of which are extant. Twenty species have colonized the state since 1900 including 14 since 1950. Of all extant species, 102 (48%) are considered common at least somewhere in the state and 64 (30%) are rare to very rare. Diversity varies by physiographic region with 179 (83%), 168 (78%) and 141 (66%) in the Coastal Plain, Mountains and Piedmont, respectively. Two significant landscape features make significant contributions to the statewide diversity including tidal waters along the coast and isolated spruce-fir forests of the Appalachians that represent Pleistocene-era relicts. In all, nearly 25% of the statewide avifauna is either wholly or nearly confined to tidal water and 10% is confined to "sky island" refugia. Since 1978, 25 species of birds throughout Virginia have been identified as requiring immediate conservation action. A retrospective assessment shows that 5 of these species including osprey (Pandion haliaetus), bald eagle (Haliaeetus leucocephalus), peregrine falcon (Falco peregrinus), brown pelican (Pelecanus occidentalis) and piping plover (Charadrius melodus) have recovered to or beyond historic numbers. Three species including Bewick's wren (Thryomanes bewickii), Bachman's sparrow (Peucaea aestivalis) and upland sandpiper (Bartramia longicauda) have been lost from the state and the black rail (Laterallus jamaicensis), loggerhead shrike (Lanius ludovicianus) and Henslow's sparrow (Ammodramus henslowii) are in imminent danger of extirpation. Several species including the peregrine falcon, piping plover, Wilson's plover (Charadrius wilsonia) and red-cockaded woodpecker (Picoides borealis) are the focus of intensive monitoring and management programs. The underlying causes of imperilment remain unclear for several species of concern, limiting our ability to development effective conservation strategies.
Full-text available
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.
Migration and nesting of Florida Bald Eagles
  • C L Broley
Broley, C. L. 1947. Migration and nesting of Florida Bald Eagles. Wilson Bulletin 59:1-68.
Virginia bald eagle nest and productivity survey: Year 2010 report
  • B D Watts
  • M A Byrd
Watts, B. D. and Byrd, M. A. 2010. Virginia bald eagle nest and productivity survey: Year 2010 report. Center for Conservation Biology Technical Report Series, CCBTR-10-09. College of William and Mary, Williamsburg, VA. 40 pp.
Bald eagle survey for Chesapeake Bay
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The Chesapeake Bay eagles: Summary Report -1936; 1955-1965
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Unpublished report of bald eagle nest survey of the Chesapeake Bay region
  • W B Tyrrell
Tyrrell, W. B. 1936. Unpublished report of bald eagle nest survey of the Chesapeake Bay region. National Audubon Society, Washington, D.C. 30 pp.
Bald Eagle survey: first annual report
  • J M Abbott
Abbott, J. M. 1957. Bald Eagle survey: first annual report. Atlantic Naturalist 12:118-119.
Chesapeake Bay region bald eagle recovery plan: First revision. U.S. Department of the Interior, Fish and Wildlife Service
  • M A Byrd
  • G D Therres
  • S N Wiemeyer
  • M Parkin
Byrd, M. A., Therres, G. D, Wiemeyer, S. N., 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, MA. 49 pp.
Recovery of the Chesapeake Bay bald eagle nesting population
  • B D Watts
  • G D Therres
  • G D Byrd
Watts, B. D., G. D. Therres, G. D., and Byrd, M. A. 2008. Recovery of the Chesapeake Bay bald eagle nesting population. Journal of Wildlife Management 72:152-158.