Keeping track of migrating raptors
Scientists in Washington State monitor the populations and migration patterns of birds of prey, to identify trends.
The instant a black dot appears on the horizon, someone calls out, “We’ve got a bird out there,” and all chatter stops. The sound of a gentle wind pushing against the ridgetop is all that can be heard as wildlife biologists and visitors raise binoculars to their eyes to study the speck coming toward them.
Silence. More silence.
“A bald eagle, maybe?” someone asks.
Moments later, “Yes, a bald eagle,” biologist Brian Connelly confirms when the raptor is close enough for positive identification.
Satisfied, his counting partner, Craig Waythomas — also a wildlife biologist — puts it down on a clipboard page marked with 18 different species of hawks, falcons, and other birds of prey that might be seen from here.
Over the last 13 years, biologists have counted more than 27,000 raptors from this 5,500-foot ridge that separates the Methow and Chelan valleys. It’s about 40 miles northeast of Wenatchee. In the past 11 years, they’ve captured and banded more than 6,000 birds of prey, starting the leg-banding after two years of counting confirmed this was a good migratory route for birds of prey from late August to late October.
Principal biologist Kent Woodruff, who works for the US Forest Service in the Methow Valley Ranger District, says the collaboration between the nonprofit conservation group HawkWatch International and the Forest Service gathers valuable baseline data that will help determine when a species is in trouble.
“One of the things we’re learning is that raptor populations fluctuate, and some of that fluctuation is normal,” he says. A drop in the count of one species over a few years is no cause for alarm, he says. But over a decade, it becomes a trend, and can be an indicator that something’s wrong. The data so far shows no trends, up or down, of any of the hunting birds they count. “We haven’t seen anything that would be cause for action,” Mr. Woodruff says.
Each year, they count and capture everything from the extremely common sharp-shinned and Cooper’s hawks, to the less-often-seen prairie and peregrine falcons.
Among the rarest sightings from this location is the broad-winged hawk. Over the years, they’ve counted only 62 from this location of the tens of thousands of birds identified. On Sept. 28 they trapped and banded the first broad-winged hawk ever captured in Washington state.
The species is common in the eastern United States, but is apparently expanding its range to the west, and migrates now from British Columbia, Woodruff says. The one they banded was a “dark morph,” or bird with unusually dark feathers for its species.
The event was a highlight of the summer. Biologist Robert Spaul calls it luck. He knew almost immediately what he had, despite its unusually dark color. “It threw me off for a couple of seconds. But as I pulled it out of the net I was like, ‘Oh, wow! This is something special.’”
Mr. Spaul is one of two biologists who work the capture stations on Chelan Ridge, known as North Blind and South Blind. He uses live pigeons under plastic cover to attract the raptors, which trigger a net to fall when they attempt to catch the protected bait.
Once the raptor is caught, Spaul takes measurements, like leg length, beak length, and length of the longest talon. This helps determine if they’ve captured a male or female. They also weigh the bird, and take notes on its plumage.
Chelan Ridge is one of six places where HawkWatch International captures and bands birds of prey, and one of 13 counting sites.
Woodruff noticed it might be a hawk migration area about 15 years ago, when he was flying over the ridge looking for smoke as part of his Forest Service duties.
He sent someone up to investigate, then called his good friend, Steve Hoffman, who happened to be the director of HawkWatch International at the time.
A biologist with ornithology as an area of emphasis, Woodruff knew that ridge lines are often migration routes for raptors if the prevailing winds create what’s known as ridge lift. “It makes it easier for hawks to migrate without expending as much energy,” he explains.
A year later, the counting surveys started, and that was so successful they decided to make it a banding area.
“For me, it’s one of the most rewarding and meaningful projects I’ve done in my career,” Woodruff says. He says he’s constantly impressed with the dedication of the biologists, who put in many volunteer hours. “It gives young biologists an opportunity to learn about good science and allows us to share some of what we’ve learned with the public.”
Data has already been used in a publication last year on the status of raptors called, “The State of North American Birds of Prey.”