Rather grim news to share. This article was passed to me from a friend who
works documenting West Nile cases.
West Nile virus may be killing raptors by the thousands
Massive die-off of birds strikes Midwest
Sunday, October 20, 2002
By Don Hopey, Post-Gazette Staff Writer
Thousands of hawks, eagles, kestrels, falcons and owls have died in recent
months in a swath of the United States from Minnesota to the Gulf of Mexico
and Nebraska east through Ohio into Pennsylvania.
West Nile virus was-and still is-a prime suspect in the raptor deaths. But
tests on some of the dead birds show they were not infected, and avian
experts are investigating other factors that could be acting alone or in
combination with the virus to bring the big birds down.
Southwestern Pennsylvania appears to be on the edge of the massive and
mysterious raptor die-off that has taken a tremendous toll on birds in the
broad Midwest but, for reasons that are still unclear, have resulted in few
raptor deaths and affected fewer species from the Appalachian Mountains to
the East Coast.
Large numbers of crows and blue jays and a few red-tailed hawks, great
horned owls and kestrels have died of West Nile in the East, but it's
nothing like the toll in the Midwest, including southwestern Pennsylvania.
"We've lost a great horned owl we use for educational programs to what we
believe is West Nile, and also a red-tailed hawk," said Rozanne Wilson,
director of the Pennsylvania Wildlife Center in Penn Hills. "Luckily, two
birds-a short-eared owl and a screech owl-in cages right next to them didn't
She said another great horned owl and three of five hawks that were brought
to the center while displaying classic West Nile symptoms-low body weight,
inability to walk straight or identify food, head twitches-also died. The
other two hawks are recovering and could be released soon.
"It looks like West Nile but we don't know for sure," Wilson said.
"Whatever it is, it's hit us hard."
Patricia Bright, director of the pesticides and birds program for the
American Bird Conservancy in Plains, Va., said her organization guessed that
the number of dead raptors was in the thousands.
"But there are no hard numbers," she added. "And wherethey do have them
they're usually dramatically understated because sick birds sequester
themselves and dead birds are hard to find.
"The real concern is what effect this will have on long-term raptor
populations. The ones with high reproductive rates will be OK, but the
concern comes when birds like the California Condor, which are already
existing in low numbers, get it."
Birds serve as hosts for West Nile virus, which is spread by mosquitoes to
other birds as well as to humans, horses, squirrels and dogs. The virus can
cause encephalitis, a potentially fatal inflammation of the brain and spinal
cord, but only a very small percentage of humans who contract the disease
suffer any ill effects. Many birds also contract West Nile, but only a small
The virus cannot be spread from person to person or from birds to humans.
While many of the dead birds have tested positive for West Nile virus,
others have not. Even birds that display West Nile symptoms have tested
negative for the virus.
Wildlife Works Inc., an animal rehabilitation center in Youngwood, Fayette
County, has taken in 29 raptors since July and had 17 die. Ten of the birds
were sent to state labs for testing, but only one of the six test results
returned to the center so far was positive for West Nile.
"We're still waiting for the other results but so far we don't have the
information to make sense of what's happening here," said Beth Shoaf, a
wildlife rehabilitator. "Something has gone on out there that is outside of
the norm. We'reseeking other diagnostic help."
Shoaf said the neurological symptoms displayed by the birds-head tremors,
difficulty swallowing, inability to recognize food-are also suggestive of
exposure to pesticides or some other environmental toxin.
Some longtime observers of raptors are blaming the Hippoboscid fly- actually
a group of bird parasites also known as louse flies or flat flies. The
flies proliferated because of last year's mild winter and infested birds of
prey in unusually large numbers this summer. The flies feed on blood in the
quill of emerging feathers on large birds.
"We want to be able to deal with the situation, whatever it is," Shoaf said.
"It would be nice to establish some sort of research team to document the
clinical signs and find out what's happening."
A fistful of theories
At the Hawk Mountain Sanctuary in central Pennsylvania, the annual fall
raptor migration is in full swing with scarcely a ruffled feather. There
have been no reports of raptor mortality and the "kettles"-swirling flocks
of hawks riding the columns of warm air rising against Kittatinny
Mountain-have been as full as or fuller than ever.
"I've had a lot of questions, but we haven't seen any decline. Migration
counts have been incredible," said Mary Linkevich, a Hawk Mountain Sanctuary
spokeswoman. Sightings of bald eagles are on record pace for the year and
the 31 peregrine falcons sighted Oct. 5 broke the old one-day record of 11
established in 1937.
"We're very pleased with what we're seeing here," she said. "Unfortunately
we have heard about the raptor deaths and know about the declining numbers
in other areas."
Why raptors are dying in greater numbers in the Midwest than they are in the
East is a question still in search of an answer, but one that's hatched many
One is that the West Nile virus could be mutating as it moves west,
developing a strain that is more deadly to bird populations. Another is that
bird populations in the Midwest are genetically different than those in the
East and for some reason more susceptible to West Nile virus.
A third theory holds that the birds, already weakened by West Nile, are
being killed off by other viruses, bacteria or pesticides. Or it could be
that different species of mosquitoes in the Midwest may target raptors over
Yet another theory holds that raptors in the East have long been exposed to
Eastern equine encephalitis, a virus related to West Nile, and have
developed an immunity to it.
"There's a whole lot of variables out there and a lot more questions than
answers," Bright said. "Something else other than just West Nile is going on
out there, but we don't know what it is."
Chuck Tague, a Pittsburgh area naturalist and publisher of Nature Observer
News, said his concern was that migrant birds will become infected with West
Nile virus as they move through the area.
"If they spread the disease to other birds, that could well weaken them and
affect their migration next spring," he added.
Earlier this month, a red-tailed hawk Tague often featured in his nature
talks died after exhibiting West Nile symptoms.
"I'm afraid we're just seeing the beginning of something here," he said.