Pittsburgh — A ground-breaking effort to protect northern goshawks from West Nile virus is also enabling wildlife biologists to learn more about the secretive, forest-dwelling raptor that was state-listed as endangered in October.
In what is believed to be a first, state game officials captured a nesting female goshawk in June to vaccinate her against the deadly disease. They then color banded the bird for future monitoring.
Although just three active goshawk pairs are known to exist in Pennsylvania – down from 150 to 200 pairs 30 years ago – biologists now are working to see if there are more, and how they can best be protected. They, too, would be vaccinated.
Mosquito-borne West Nile is one of many threats to goshawks, a species also impacted
by commercial logging, oil and gas drilling, climate change, predation,
and prey availability, according to Pennsylvania Game Commission
ornithologist Sean Murphy.
“The vaccine is very safe, it has been used on goshawks in captivity, and if it gives
the few goshawks that we have a leg up against exposure should they get
bitten by an infected mosquito, there’s not much downside to this
—Veterinarian Andrew DiSalvo
He characterized Pennsylvania’s greatly-diminished population as “the canary in the coal
mine,” noting that goshawks are extirpated in neighboring Maryland and
West Virginia, which are part of the species’ southernmost range.
“If you want to reverse the trend in declining numbers, you have to
minimize threats,” he said. “Pennsylvania still has birds to hopefully
maintain and we want to help the species rebound.”
The process began in March when biologists installed a dozen autonomous
recording devices to collect sounds in areas known to have historically
March is when goshawks are vocally courting to pair-bond.
The units were programmed to activate in the hours immediately before and
after dawn, “which would be the goshawks’ noisiest time of day,” Murphy
A Penn State student developed a program that would enable scientists to isolate the
signature goshawk call from other forest sounds and transcribe it in a
read-out similar to an electrocardiogram. The devices were moved every
couple of weeks in 30 different areas in the state.
When one of the units detected a goshawk, biologists went to search for a
nest and found one 35 feet up in a tree, Murphy said. “At first, they
thought it was an old nest, but on a second visit they saw the tail
feathers of an adult goshawk so it turned out to be an active nest.”
Given the delicacy involved in handling such a rare bird, scientists,
including state wildlife veterinarian Andrew DiSalvo and Maryland-based
goshawk expert David Brinker, carefully planned their operation to
capture and process the adults in June, by which time they were tending
to two chicks.
The crew set up a robotic, “taxidermied” great-horned owl to try to lure the
adults into leaving the nest, and a mist net that would collect them
when they did.
“Great-horned owls are a known goshawk predator, so presenting that temporary
threat on a territorial pair, when they have chicks to protect, can make
the goshawks very aggressive,” Murphy said.
His crew operated the roboowl’s sounds and head and wing movements from inside a blind stationed 40 feet from the goshawks.
It worked, at least with the female, DiSalvo said. “The adult birds began
calling to each other and became very agitated. There were five to 10 of
us on the ground, so they weren’t happy about that, either. The female
dive-bombed the decoy.”
As soon as she hit the mist net and got tangled, scientists swaddled her
“like a burrito” to secure and protect her wings, DiSalvo said, and
fitted her with a hood to minimize her stress.
A blood sample was drawn to determine whether she was infected with West
Nile or other diseases and then she was banded and vaccinated.
Banding was important because goshawks are site-faithful and while the female
isn’t expected to return to the same tree next spring, she is likely to
nest within 500 meters of this year’s base.
Although tree climbers were part of the crew, the decision was made not to band
the chicks because they weren’t old enough to be able to fly and “we
didn’t want to spook them into trying to leave the nest,” DiSalvo said.
When a scientist returned to the site a week later, he found that the
nestlings had fledged and were perched in nearby trees and the female
appeared to be fine, Murphy said.
Vaccination of wildlife is “a bit controversial,” DiSalvo said, given the
difficulty in capturing animals to deliver shots, and the feasibility of
such an effort.
“It takes a lot of legwork.
Where it makes sense is where you have these really small populations.”
It would be useful, for example, for wildlife rehabilitators to be able to
administer a West Nile vaccine if they are brought an injured goshawk.
And while there is some risk in the pilot inoculation program, it is outweighed by the benefits, he explained.
“The vaccine is very safe,” he said. “It has been used on goshawks in
captivity, and if it gives the few goshawks that we have a leg up
against exposure should they get bitten by an infected mosquito, there’s
not much downside to this approach.”
More autonomous recording devices will be installed next year as part of an
overarching goal to assess goshawk numbers and implement conservation
Documenting nest locations would ensure greater protection when loggers and oil and gas companies seek permits for their activities, and would influence forest management decisions, Murphy
As an example, he pointed out that the Game Commission is looking to change the way
game lands roads are engineered to reduce standing water and, thus, mosquitoes.
Goshawks are not the only avian animal vulnerable to West Nile. The virus, which
causes inflammation of the brain, also is impacting ruffed grouse,
turkeys and bald eagles.