ANNAPOLIS, Md. — Maryland’s bald eagle population has surged from 44 breeding pairs in 1977 to over 1,400 in 2025, a recovery driven by pesticide bans, habitat protections, and dedicated monitoring. Glenn Therres, a retired Maryland Department of Natural Resources biologist, documented this rebound through annual aerial surveys from 1985 to 2004, spotting nests from a Cessna plane. The resurgence, fueled by the 1972 DDT ban and Chesapeake Bay restoration, marks a conservation success under the Endangered Species Act.
Therres, who retired in 2021, recalled the early surveys, saying, “Every year we would find additional nests and map the new locations.” Starting with 62 breeding pairs in 1985, the count grew to 123 by 1990, 200 by 1996, and 390 by 2004, when the Department of Natural Resources ended the survey after surpassing recovery goals. Surveys initially required three days but expanded to nine or 10 days by the end to cover the growing number of nests.
The bald eagle’s decline stemmed from DDT, a pesticide that caused eggshell thinning and reproductive failure. By 1963, only 417 nesting pairs remained in the lower 48 states. The Environmental Protection Agency’s 1972 DDT ban allowed populations to recover. Dave Brinker, a Department of Natural Resources conservation ecologist, noted, “Bald eagles are a very good example of what happens when you find the solutions and take action, and now you can look at how they’ve come back.”
Gwen Brewer, a Department of Natural Resources science program manager, emphasized the societal effort, stating, “To recover a species that is so widely distributed and that declined to such a serious level—that is something to celebrate.” The Chesapeake Bay Protection Act of 1984 safeguarded nest sites by restricting development within 1,000 feet of tidal waters, further supporting recovery.
Aerial surveys, started by the Audubon Naturalist Society in 1977 and taken over by the Department of Natural Resources, involved low-altitude flights over waterways. Therres described the challenging conditions, saying, “It took a strong stomach and inner ear because we were flying donuts around the nests.” Flights in February or March located nests, with May or June follow-ups to count near-adult-sized nestlings.
Since 2004, the Maryland Bird Conservation Partnership has coordinated volunteer nest monitoring. Gabriel Foley, the partnership’s executive director, said, “MBCP’s Bald Eagle Nest Monitoring Program is a great example of how anyone can help make sure eagles remain a common sight in Maryland.” Volunteers track nest success and population trends, aiding conservation efforts.
The Chesapeake Bay hosts the highest bald eagle concentration outside Alaska, supporting local, southern, and northern eagle populations seasonally. Brinker explained, “In the winter, northern populations that need a warmer place, they come down to the Chesapeake Bay.” Despite ongoing threats like avian flu, bald eagles now nest in every Maryland county and Baltimore City. Nationally, the species was reclassified as threatened in 1995 and delisted in 2007.
