ANNAPOLIS – Bird lovers and biologists are monitoring rising bird deaths in Maryland after the fourth raptor – a hawk found in Dorchester County – was found last week to have died from West Nile Virus.
“We’re keeping our eyes and ears open, because we know that there has been a big increase” in deaths of owls and hawks in other states, said Glen Therres, endangered species expert with the Department of Natural Resources. “But it doesn’t look like it’s affected our birds to that point yet.”
Raptors are of special concern because their populations are smaller and more spread out, although other bird species have lost greater numbers, said John Bianchi, National Audubon Society spokesman.
“It’s not a huge problem with most birds,” he said. “What we are concerned with is those that have a real small population. That comes down to two groups – raptors and rare birds.”
In Maryland’s neighboring Pennsylvania, significant numbers of raptors have fallen prey to the disease. Of 168 sharp-shinned hawks found dead, 79 had West Nile virus, along with four of 42 owls and 44 of 135 red-tailed hawks, said Pennsylvania health department spokesman Richard McGarvey.
Pennsylvania’s game commission was most concerned about endangered raptors like bald eagles, ospreys, short-eared owls and peregrine falcons. Those species also are found in Maryland, although their populations here have not suffered the same losses from the virus.
“We’re seriously concerned about West Nile having an impact on those four species because of their low numbers already,” said commission press secretary Jerry Feaser. Other raptor species, such as red-tailed hawks and great horned owls, would be able to recover from the virus, he said.
The virus is a “bird disease,” Bianchi said, though it doesn’t always kill susceptible birds. They are infected the same way humans are – from mosquito bites – but some can carry the virus in their blood for a few days before becoming immune to it, according to the Centers for Disease Control and Prevention.
Reports of rising deaths among raptors in the Midwest alarmed the Raptor Center at the University of Minnesota in St. Paul. More than 100 great horned owls and red-tailed hawks were affected in Ohio, according to a Sept. 3 news release. Indiana, Kentucky, Michigan and Iowa each reported “dozens” of infected raptors. But the number of sick or dead birds reported has dropped since then, and is likely to continue dropping as the colder weather reduces the number of mosquitoes that transmit the virus, said the center’s Dr. Pat Redig.
All but six states in the west – Arizona, Idaho, Nevada, Oregon, Washington and Utah – have reported bird, human or animal cases of West Nile virus, according to the CDC. While colder weather will reduce reports nationwide, birds’ winter migration patterns may also be “a potential source of transmission of the disease from affected areas to unaffected areas,” Therres said.
West Nile virus has been found in 525 birds across Maryland, with about one-fifth in Montgomery County. More than three-quarters were crows, and 61 were blue jays, which belong to the same family of birds. These are common species, so their deaths so far are not a “serious conservation consequence,” Therres said.
But the bird found in Dorchester County was a sharp-shinned hawk, a regular Maryland winter migrant. Two owls and two hawks, including the Dorchester bird, have died of the disease in Maryland, said Department of Health and Mental Hygiene press officer J.B. Hanson.
Scientists are not yet certain why crows and their relatives, or raptors, are so much more susceptible. Bianchi likened the effect of the virus to “unleashing a nonnative predator.” Like humans in the U.S., American birds are coming into contact with this disease for the first time populationwide, and it will take some time before its effects are fully understood. “This disease is relatively new on the wildlife radar screen,” Therres explained. “Every year we’re learning a little bit more about its impact. Where it’s headed from here, we’re just going to have to wait and see.” – 30 – CNS-10-1-02