Last year, West Nile came within eight miles of the 12,800 acres of marsh and woodland of the Geological Survey's Patuxent Wildlife Research center, when a crow died of it in nearby Howard County, according to [Glenn H. Olsen], the Patuxent cranes' chief curator.

"We're very concerned about the West Nile virus, because we don't know how serious a health threat it poses," Olsen said yesterday at the refuge's veterinary hospital. "We do know that [the cranes are] susceptible to other mosquito-borne viruses.

West Nile also comes in the midst of elaborate efforts to increase the number of whooping cranes in the wild. This fall, conservationists will use 15 Patuxent birds, led by an ultralight aircraft, to try to establish a wild flock and a migratory route from Wisconsin to Florida. The last thing the project needs is its cranes dying of the virus, Olsen said.