October 2008

Rescuing the Raptors

A common household rodent poison can kill birds of prey, but help is on the way

By Jacqueline Mitchell

When the red-tailed hawk came barely responsive into the clinic, Tufts wildlife veterinarian Maureen Murray, V03, knew the prognosis wasn’t good. Found in Boston, the bird’s oral tissues were pale, instead of a normal healthy pink, and the blood oozing from a small wound on its shoulder showed no signs of clotting.

Raptors such as the red-tailed hawk that eat poisoned rodents face slow death, but new EPA regulations may be a lifesaver. Photo: iStockphoto

“These two things together immediately made me think of rodenticide,” toxic chemicals intended to kill rodents, says Murray, who began a course of treatment that saved the bird’s life. Murray and Flo S. Tseng, director of the Wildlife Clinic at the Cummings School of Veterinary Medicine, described the lifesaving treatment protocol—a six-week regimen of fluids, blood and vitamin K—in the Journal of Avian Medicine and Surgery.

Red-tailed hawks (Buteo jamaicensis), sometimes called chicken hawks, are medium-sized birds of prey found throughout North America, Central America and the West Indies. Opportunistic carnivores, the hawks dine on whatever birds and mammals are available. Their diverse diet and love of tall perches like skyscrapers and telephone poles mean they are perfectly happy in cities, feasting on mice and pigeons. Unfortunately, the measures we take to get rid of those pests can harm the birds that hunt them.

The red-tailed hawk that arrived at the clinic in March 2006 wasn’t the first poisoned hawk Murray and Tseng had seen that spring. Lab results for two dead red-tailed hawks had come back positive for brodifacoum, a common over-the-counter rodent poison. Brodifacoum is a particularly potent member of a family of anticoagulants that kills by inhibiting blood clotting, damaging blood vessels and causing hemorrhaging.

Rodents poisoned with the stuff die over the course of several days, becoming more lethargic—and increasingly easy targets for birds of prey. Because the toxin metabolizes slowly and accumulates in the liver, a raptor feeding on poisoned rodents can build up toxic levels over time.

A recent survey of 265 dead birds representing 12 different species in New York City found residues of anticoagulant rodenticides in half the birds’ livers. Murray has been testing the livers of the birds of prey that come through the Wildlife Clinic, and has found that “a pretty high percentage do have low levels of rodenticides,” though the majority don’t have enough in their systems to get sick.

The Wildlife Clinic sees a half-dozen birds each year that show signs of rodenticide poisoning, says Murray. The research results that she and Tseng published are the first to describe the symptoms and the successful treatment of a live red-tailed hawk.

Turning the Corner

Symptoms of brodifacoum poisoning differ between birds of prey and mammals. In dogs and humans, the toxin causes bleeding into the chest cavity, which can be seen on X-rays. Raptors suffer from bruising and extreme anemia. This hawk had both: bruising on the torso and a red blood cell count of 9 percent (38 percent is normal). The oozing wound on the hawk’s shoulder was also typical; a 1999 study reported about a third of poisoned birds had a minor cut that wouldn’t clot.

Ideally, the veterinarians would have given the hawk a transfusion of blood from another bird of the same species. But “we often don’t have a donor as readily for birds as we do for dogs and cats,” says Murray.

So the chicken hawk was given fluids, commercially available blood products and heavy doses of vitamin K, the established antidote to brodifacoum, which kills by interrupting a clotting mechanism mediated by the nutrient. This restorative elixir had to be delivered via a catheter inserted into the bone, since the hawk was so dehydrated that its veins were “really collapsed,” says Tseng.

On the third day of treatment, the hawk “dramatically turned the corner;” it was standing and alert, says Murray. The bird’s blood levels were better, but still low, so Murray and Tseng continued the fluids and vitamin K therapy, served with toxin-free mice dinners. Perhaps having learned its lesson about rodents, though, the bird refused the mice. Meals of vitamin K-laced quail, however, were an instant hit. After 10 days of treatment, the hawk had a normal blood cell count.

After six-weeks, the hawk was healthy again, a tiny sample of its blood clotting in under two minutes. The bird was banded and released near the clinic in Grafton, Mass., where there is less chance of it preying on poisoned mice or rats than in the city. Murray and Tseng have not heard any reports of the bird. Both say that no news is good news.

This past spring, the Environmental Protection Agency moved to enact regulations to better control the use of brodifacoum and nine other potent anticoagulant poisons. The new rules will restrict household, but not commercial, use of these poisons. The changes won’t happen for three more years, but it’s a step in the right direction, says Murray. “A lot of people who use [brodifacoum] have no idea the danger they pose to wildlife,” she says.

Still, three more years of easy availability of the stuff could mean roughly 18 more poisoned raptors at the Wildlife Clinic. Murray and Tseng’s treatment protocol could make the difference at wildlife clinics nationwide—even worldwide. “The prognosis is not great when they are this down and out,” says Tseng. “We’re very happy when we can bring them back from the brink.”

This story first appeared in the Summer 2008 issue of Tufts Veterinary Medicine magazine. Jacqueline Mitchell can be reached at jacqueline.mitchell@tufts.edu.

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