Birds of Prey Fall Victim to West Nile Virus

Although Susan Ahalt has tended sick golden eagles, red-tailed hawks and other birds of prey for 14 years, losing one still bothers her. So the last few months have been tough as she has watched West Nile virus take its toll on raptors.

“It rips your heart out to work and work on these birds and there’s nothing you can do,” Ahalt said. She’s had at least three confirmed West Nile cases -- including two golden eagles -- and others she’s only suspected in birds she treats at a rehabilitation center in northern Wyoming. “It’s devastating and I hate it.”

West Nile, the mosquito-borne virus first reported in this country in 1999 and now spreading West, reached the Rocky Mountain states last year and hit hard this year. West Nile infects humans, birds, horses, cats and other animals. But humans are the essential health focus.

Colorado was hit particularly hard this year. By early October, the state had reported 2,090 human cases of West Nile, and 38 deaths, to the Centers for Disease Control and Prevention. Also hard hit were Nebraska, South Dakota and Wyoming, which each reported hundreds of human cases.

But while attention has been fixed on keeping people safe, West Nile has also taken a largely unseen toll on eagles, owls, hawks and other birds of prey.

Many raptor centers in those states are being inundated with birds that officials often describe as weak, disoriented, off-balance or plain sickly. West Nile symptoms in raptors can be vague and resemble trauma, starvation or even poisoning.

The virus is taxing the limited resources of rehabilitation centers that rely on financial aid and volunteer help. And it’s leaving many bird lovers used to helping raptors -- and who need permits to work with birds of prey -- feeling helpless.

More than 210 birds have been admitted this year to the Rocky Mountain Raptor Program at Fort Collins, Colo. The center’s director believes that many have had West Nile -- a belief Judy Scherpelz said she bases on gut instinct and some blood tests.

Tending for sick birds requires extra time and money. It can take eight weeks of intensive care before a raptor that survives West Nile can perch or even eat on its own again, she said, and longer for it to build up its strength and learn to fly. Even the recovery period can be fatal to a bird in the wild.

“Think of it as a human that’s had a severe neurological disease; it’s going to be a long time before they run a marathon,” she said. “A bird in the wild is a performance athlete. It must go from not being able to stand back to being a performance athlete.”

Some species may be more affected by the virus than others, and the virus may affect different species in different ways, said Patrick Redig, a professor and director of the Raptor Center at the University of Minnesota College of Veterinary Medicine.

“Great horned owls, by and large, tend to exhibit more severe neurological signs -- imbalance, seizuring, the nobody’s-home kind of thing,” he said. “Red-tailed hawks present more as a very sick bird. But the outcome is largely the same -- and they die from it.”

Tallying West Nile cases among great horned owls, peregrine falcons and other raptors -- even getting rough estimates -- is difficult because many birds were not tested and not all cases were reported to state public health agencies, said Emi Saito, West Nile surveillance coordinator for the U.S. Geological Survey’s National Wildlife Health Center at Madison, Wis.

“Last year was the first year we heard about large numbers of raptors being affected, primarily in Midwestern states,” she said.

Crows are highly susceptible to West Nile and are watched closely because they can tip public health officials to the virus’ spread, said John Pape, Colorado Department of Public Health epidemiologist.

“By testing that type of bird, we can track and check hot spots,” he said, noting the overall goal of early detection.

How West Nile will affect raptor populations in the long run remains unclear, wildlife officials said, noting that the size of many of those populations was unclear even before West Nile.

But Saito said that what does seem clear is that “it’s here to stay. It’s going to be in the background.... As far as what’s going to happen, I don’t really know.”