Among more than 30 species of birds and mammals known to scavenge deer carcasses in New York state, bald eagles are the most vulnerable to lead poisoning from hunters’ ammunition and best bioindicator for ongoing monitoring of the hazard, new Cornell research finds.

Analyzing game camera images contributed by New York residents, the researchers developed the state’s first comprehensive list of scavengers of white-tailed deer, identifying 14 birds and 17 mammals, from American crows to Virginia opossums. Considering each species’ numbers, physical traits and opportunity to scavenge – especially during big-game hunting season – the team determined bald eagles are most at risk from ingesting toxic debris from lead bullets, which fragment on impact.

The findings validate that the New York State Wildlife Health Program – a partnership between the Cornell Wildlife Health Lab and the Department of Environmental Conservation (DEC) – has been focusing on the correct species. Because the public reports sick or dead bald eagles more than other scavengers, many more are tested for lead and necropsied, including at the College of Veterinary Medicine’s Animal Health Diagnostic Center.

“A surprising number of species are at risk, and we can use bald eagles to continue to monitor lead issues because they are quite vulnerable,” said Krysten Schuler, a wildlife disease ecologist in the College of Veterinary Medicine who directs the Cornell Wildlife Health Lab. “With this list, we’re expanding our lead testing to more species and will think more broadly about lead exposure in these animals over time.”

Schuler is a co-author of “Vulnerability to Lead Toxicosis and Bioindicator Utility of Deer Scavengers in New York,” published Aug. 9 in the Journal of Wildlife Management. The first author is Dr. Andreas Eleftheriou, a visiting scientist with the U.S. Geological Survey’s Eastern Ecological Science Center and a former One Health fellow at the Cornell Wildlife Health Lab. Co-authors from the DEC, which funded the study, are Kevin Hynes, director of the Wildlife Health Unit, and Michael Clark, a wildlife manager, co-chairs of the multiagency New York State Lead Ammunition Working Group, whose members include Schuler.

Used by most deer hunters, lead bullets break apart on impact into hundreds of shards and particles that can spread well beyond a wound channel. A piece of lead smaller than a grain of rice can kill an eagle, and no amount of the neurotoxin is considered safe for humans – particularly pregnant women and children – who might unwittingly consume it in game meat.

Prior research by Cornell and DEC collaborators found lead exposure from hunters’ ammunition to be widespread among bald eagles, with nearly 40% of the study sample suffering from toxic levels. In the northeast and in New York, researchers estimated that lead poisoning had slowed bald eagles’ population growth rate by about 5%, limiting their resilience to other threats.

In a 2022 report, the Lead Ammunition Working Group encouraged hunters to choose non-toxic bullets, or to remove or bury carcasses and gut piles that attract eagles and other scavengers. The DEC has incorporated information about lead alternatives into hunting education courses and shared “Your Choice of Ammunition,” a Cornell-produced, evidence-based video featuring hunters and instructors. The state also implemented a pilot rebate program for non-lead ammunition that is now available statewide.

While studies had documented scavengers in North America and Europe, the working group wanted to know which other species might be at risk in New York. The research team reviewed nearly 160 images from 33 game cameras focused on white-tail deer carcasses, captured between 2010 and 2023. Scavenging birds identified included eagles, hawks and owls, but also mourning doves, woodpeckers, cardinals and blue jays. Scavenging mammals included coyotes, bobcats and foxes, plus squirrels, weasels and skunks.

“It’s like a big buffet,” Schuler said of the deer remains. “Everybody shows up for it.”

The researchers categorized 17 species as having higher vulnerability to “bullet-derived lead,” with bald eagles followed by golden eagles (not common in New York), American goshawks, American crows and common ravens. Some scavengers are less exposed because they migrate or hibernate during parts of the hunting season.

Encouraging a transition to non-lead ammunition is a complex sociopolitical issue, Eleftheriou and Schuler write in a related article in the Wildlife Society Bulletin. Rebate programs incentivizing voluntary adoption of lead alternatives – typically all-copper bullets – are a promising strategy, they suggest.

“It’s an opportunity for hunters to try non-lead ammunition risk-free,” Schuler said. “The more people try non-lead ammo, the more they’ll find that it performs really well and that it’s good for human and wildlife health.”