Disease hitting Midwest raptors especially hard

By Jeff Cole
Milwaukee Journal Sentinel
October 29, 2002

Town of Fredonia - The red-tailed hawk perched in a cage at Pine View Wildlife Rehabilitation Center didn't look sick as it eyed Jean Lord, the center's executive director.

But the raptor was ill. Like hundreds, possibly thousands of other wild birds, the hawk had West Nile disease. Lord was nursing it back to health.

Lord and other professionals who rehabilitate injured and sick wild birds say the virus has ripped through wild bird populations like nothing else they have ever seen.

The hawk was lucky because Lord was able to help it. But, wildlife professionals fear that other birds will not be as fortunate. There is a growing concern that West Nile is devastating wild bird populations in Wisconsin and throughout the Midwest.

"The fear is that the disease is going to affect species such as the bald eagle, the California condor, the Mississippi sandhill crane and others whose entire populations are only in the double digits," said Emi Kate Saito, a wildlife veterinarian and the West Nile surveillance coordinator at the U.S. Geological Survey's National Wildlife Health Center in Madison.

The Raptor Education Group in Antigo was raising 39 common terns, which despite their name are very rare in Wisconsin, said Marjorie Gibson, the group's director. Thirty-six of the chicks died this summer. Initial testing has found that at least some of the chicks died as a result of West Nile. Test results for the other birds are still pending.

The center was able to release the surviving three into the wild to join the 370 pairs of common terns in Wisconsin, Gibson said.

"We are hoping they have a natural immunity," Gibson said.

The disease seems to be hitting raptors particularly hard in the Midwest, something that was not seen to that degree in the East when the disease was first detected in 1999.

"From what I can tell, West Nile showed up in the Midwest first near Cincinnati and then moved northwest," said Patrick Redig, director of the Raptor Center at the University of Minnesota.

The disease has jumped to humans and other mammals. According to the federal Centers for Disease Control and Prevention, 3,346 people in the United States have been infected so far this year. Of those, 183 have died - including two in Wisconsin.

Other sources

Although it is thought that the disease is spread by mosquitoes, rehabilitation experts are starting to wonder whether raptors might be catching the virus from other sources, Lord said. West Nile has been found in squirrels, Gibson said.

"Raptors get a great deal of their moisture from the blood of their prey," Lord said. "We are concerned that they might be getting West Nile from what they eat."

Some experts also feel it is not just mosquitoes spreading the virus. There is a school of thought that feels that a parasitic fly known as the flat fly is spreading the disease from raptor to raptor.

"We had our first confirmed case this summer," said Mike Reed, a curator at the Bay Beach Wildlife Sanctuary in Green Bay. "By the end of August, it started in red-tailed hawks and great horned owls."

Birds that have the disease are lethargic to the point where they can often be approached and picked up, Reed said. However, he cautioned that it can be very dangerous to approach a raptor because if it feels threatened, it might attack.

There is no cure for infected birds, Reed said. All that can be done is feed them and hope they get better.

Some birds that appear to have kicked the disease show signs of neurological damage, Reed said. The virus seems to have affected their eyesight and coordination.

"It appears to affect their ability to digest and process food," Reed said. "We had one red-tailed hawk which seemed to be getting better. All of a sudden, it started hemorrhaging from its mouth and nose. It died.

"Eagles seem to go down particularly hard when they catch it."

Number unknown

No one knows exactly how many wild birds have been infected because many of the birds that become infected simply die without anyone knowing, said Yvonne Wallace Blane, director of rehabilitation at Fellow Mortals wildlife rehabilitation center in Lake Geneva.

Experts hope that some members of each species will have a natural immunity to the virus and pass that on to their offspring.

Cold weather will help in the short run, said Linda Glaser, West Nile surveillance coordinator with the Wisconsin Department of Health and Family Services.

"Mosquito activity is diminishing as its gets colder," Glaser said. "But it does take several hard frosts to get rid of the mosquitoes entirely, and if the weather warms up for Indian Summer, they will return."

The cold weather will eventually kill off the mosquitoes and the problem will end for the winter. But that doesn't mean the disease will go away, Glaser said. It will just go dormant until mosquitoes return in warm weather.

"I am not sure even cold weather will help," Gibson said. "We had a bald eagle come on Jan. 2, 2002. It had West Nile.

"It's possible that the virus lay dormant. Or, it could be like in humans when we have what first seems to be a mild case of the flu. Then, something happens and we get a bad case. Maybe stress brought it on in the eagle.

"There is a lot we don't know."