Approximately 30 species of birds and mammals are known to scavenge deer carcasses in New York State. But this source of food is proving a deadly option for some of them.
Many of the deer are shot by hunters and their bodies – or parts of their bodies – left on the ground. The lead ammunition embedded in their carcasses is poisonous to most scavenging animals, causing illness and sometimes death when ingested.
In a new study published earlier this week in The Wild Society journal, experts from Cornell University and the New York State Department of Environmental Conservation (DEC) found that bald eagles – the national animal of the USA – are most at risk from this bullet-derived lead poisoning.
Analysing images collected from game cameras across the state, the team of researchers documented 14 birds and 17 mammals that fed on deer carcasses and gut piles (specifically of white-tailed deer).
To assess the risk to each species, they considered their numbers, physical traits and opportunity to scavenge, eventually determining that bald eagles are most at risk from ingesting toxic debris from lead bullets, followed by golden eagles, American goshawks, American crows and common ravens.
Used by most deer hunters, lead bullets shatter on impact into hundreds of fragments that can spread through the animal's body. A piece of bullet smaller than a grain of rice can kill an eagle.
“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,” says Krysten Schuler, a wildlife disease ecologist and co-authored the study.
The study revealed that other species are less exposed, for example turkey vultures, because they are absent in the area for much of New York State’s big-game hunting season. Animals that hibernate during the hunting season are also less at risk.
“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," says Schuler.
This isn't the first time lead poisoning in bald eagles has been studied. Past analysis by Cornell and DEC collaborators found lead exposure from hunters’ bullets to be widespread among bald eagles, with nearly 40% of the study sample suffering from toxic levels. Researchers estimated that lead poisoning had slowed the growth rate of New York's bald eagles by about 5% – increasing their vulnerability 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.
Find out more about the study: Vulnerability to lead toxicosis and bioindicator utility of deer scavengers in New York
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