The latest USFWS Bald Eagle Population Update report estimates 316,708 eagles across the contiguous United States.

Bald eagle count quadruples, thanks in part to eBird data boost

For the past 50 years, the U.S. Fish and Wildlife Service (USFWS) has been assembling counts of bald eagle nests to track the triumphant recovery of America’s national symbol. But in its new bald eagle population report – tabulated with the help of results using eBird data from the Cornell Lab of Ornithology – the USFWS found many more eagles than previously thought to exist in the Lower 48 states.

A lot more.

The latest USFWS Bald Eagle Population Update report estimates more than quadruple the eagle population noted in the 2009 report, or 316,708 eagles across the contiguous United States. The rising number of bald eagles undoubtedly reflects the continuing conservation success story that stretches back to the banning of DDT in 1972. But it also represents a major advance in using citizen-science powered supercomputing to generate better estimates for the eagle population.

“Working with Cornell to integrate data from our aerial surveys with eBird relative abundance data on bald eagles is one of the most impressive ways the we have engaged with citizen science programs to date,” said Jerome Ford, USFWS migratory birds program assistant director. “This critical information was imperative to accurately estimate the bald eagle population in the contiguous United States, and we look forward to working with Cornell in the future.”

In addition, the new USFWS report estimates 71,467 nesting pairs of bald eagles in the Lower 48 states, which is double the number of eagle nests noted in the 2009 report – and many multitudes higher than the all-time recorded low of 417 known eagle nests in 1963. Back then, the popular use of DDT pesticides after World War II had decimated the eagle population. In 1967, the bald eagle received protection under the predecessor to the federal Endangered Species Act (ESA). Then in 1972, the United States banned DDT.

Thanks to legal protections, captive-breeding programs and habitat protection around nests, the bald eagle population rebounded. The USFWS tracked the recovery through counts from states and by aerial surveys every few years, as pilots from the agency’s Migratory Bird Program flew eagle-counting missions over high-density eagle-nesting areas to count numbers of occupied nests.

But for this latest USFWS report, the federal government collaborated for the first time with the Cornell Lab to augment their aerial surveys with a big-data population model generated by eBird.

The computer science that built the eBird model was powered by citizen science. More than 180,000 birders shared data with the Cornell Lab by uploading eBird checklists – tallies of which bird species they saw, and how many, in a single outing. Cornell Lab scientists then developed a model that uses eBird estimates of relative abundance for bald eagles to generate numbers of occupied nesting territories in the areas that USFWS were not able to cover in their aerial surveys.

“One of our main objectives was to see if population modeling based on eBird data would enhance the survey work the Fish and Wildlife Service was already doing,” said Viviana Ruiz-Gutierrez, assistant director of Cornell Lab’s Center for Avian Population Studies, who supervised the lab’s role in this partnership. “We’re hoping that this will allow the Fish and Wildlife Service to track bald eagle populations over a much wider area in the most cost-effective manner in the future.”

And, Ruiz-Gutierrez says, she also hopes those eagle models continue to show positive momentum. Since the USFWS delisted the bald eagle from the ESA in 2007 – a historic moment for species recovery under the act – the number of known occupied nests in the Lower 48 states has more than doubled, according to the latest report.

“It’s a great American conservation success story,” Cornell Lab Center for Avian Population Studies Senior Director Amanda Rodewald said March 24 at a virtual press conference hosted by the USFWS. She thanked the agency for hosting the event to celebrate eagle recovery, and to celebrate the role of citizen science – the thousands of birders who shared their observations to help build the population models.

“It’s heartening to see how we can all come together in different ways to conserve the birds that we all cherish,” Rodewald said. “We at the Cornell Lab hope that this is just the beginning of many more successful collaborations with the Fish and Wildlife Service.”

Gustave Axelson is the editorial director at the Cornell Lab of Ornithology.

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