From the February 2014 Conservationist
Wildlife Health Corner
A look at lead poisoning in bald eagles
By Kevin Hynes
Bald eagles have made a remarkable comeback in New York and many parts of the U.S. in the past 40 years. Once numbering only a single nesting pair, New York now boasts more than 170 breeding pairs of bald eagles. However, eagles face a largely unrecognized toxic threat from ingesting lead ammunition.
Every year, DEC's Wildlife Health Unit (WHU) diagnoses eagles that have died from lead poisoning. Most lead-poisoned eagles in New York are found in winter and early spring, when frozen waterways cause eagles to switch from a diet of primarily fish to more scavenged mammal and bird carrion, including discarded hunter-killed deer carcasses.
Immature bald eagle ready for necropsy
(Green staining of feathers near the feet
indicate the bird has not eatenfor an
extended period of time)
Fragments of lead rifle bullets embedded in discarded deer gut piles and carcass parts, or lead shotgun pellets in other game carcasses, pose a serious threat to eagles that ingest them. When an eagle (or other avian scavenger like a crow, raven, or vulture) consumes bullet fragments or shotgun pellets, the lead is dissolved by the bird's strong stomach acid and transported in the blood to the brain, where it affects the nervous system. Lead-poisoned eagles are usually found dead or in a weakened condition, unable to fly. Sometimes, poisoned birds can be treated with chelation therapy, but often by the time an eagle is captured, it is too late to be saved.
When we examine eagles killed by lead poisoning, they are typically in fair to poor body condition, have nearly empty stomachs and intestines, and may have green, bile-stained tail feathers. Interestingly, it is unusual to find lead bullet fragments or shotgun pellets in a poisoned eagle's stomach, because eagles will regurgitate pellets of undigested hair, feathers, and bone, including remaining lead fragments. We confirm lead poisoning by testing lead levels in the bird's liver or kidney. The WHU diagnosed five such cases of lead-poisoned eagles in 2011 and seven in 2012. However, it is likely that more eagles died from lead poisoning but were never found.
Lead bullet fragments from the stomach
of a lead-poisoned bald eagle.
Rifle bullets used for hunting are typically constructed of a lead core surrounded by a thin copper jacket designed to expand on impact. When the bullet hits a bone or expands inside of the target animal, small lead fragments are deposited along the wound tract. Some fragments can travel 12 to 18 inches away from the main wound channel. Big game animals like deer and bear are usually shot through the chest. The heart, lungs, and abdominal organs are removed during field dressing and are usually left in the field where the animal was shot. Eagles are opportunistic scavengers, and commonly feed on gut piles and discarded carcasses. Ingesting as few as two small lead pellets can result in clinical, if not fatal, lead poisoning.
Lead bullets (left side) fragment much
more than non-toxic copper (at right).
Non-toxic substitutes are available in many popular rifle calibers. Solid copper bullets often have better accuracy and more controlled expansion than conventional copper-jacketed lead bullets. In addition, solid copper ammunition is non-toxic to birds of prey and is comparable in price to premium-grade lead ammunition. To reduce lead exposure to hunters, their families, and eagles, DEC recommends that hunters consider using non-lead ammunition. Hunters are the original conservationists, and we hope that when they realize the potential threat lead ammunition poses to eagles and other birds of prey, they will readily make the switch to non-toxic ammunition.
Kevin Hynes is a biologist with DEC's Wildlife Health Unit in Delmar.