Big Belts nation’s No. 1 flyway for golden eagles, survey saysSource: Great Falls Tribune
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Karl Puckett , firstname.lastname@example.org
More golden eagles fly through Montana’s Big Belt Mountains than any other raptor migration site in the Lower 48, a new report has confirmed.
Primary observer and site supervisor Ronan Dugan, assisted by biologist Jeff Grayum, observed golden eagles Aug. 27 through Nov. 5.
They counted 2,620 golden eagles during that span.
“Our Big Belt count recorded the greatest number of golden eagles of any raptor migration site in the contiguous United States during fall 2016!” gushed a Montana Audubon report on the fall golden eagle migration issued last week.
The only other migration site where more migrating eagles were counted last fall was Mount Lorette in the Canadian Rockies in Alberta, said Steve Hoffman, the recently retired executive director of Montana Audubon, who helped to set up the observation site in Montana’s Big Belt Mountains.
At Mount Lorette, 3,388 golden eagles counted.
The accessibility of the Big Belts observation station to the public makes it stand out along with the high number of golden eagles that use the flyway, Hoffman said.
It’s operated by Montana Audubon, Last Chance Audubon, Helena-Lewis and Clark National Forest and Montana Fish, Wildlife and Parks.
“This is a great opportunity to enjoy one of the most amazing natural spectacles in nature,” Hoffman said.
Although people can hike to the area and watch raptors soaring past on powerful updrafts, it also can be reached by four-wheel drive vehicle.
From Sept. 1 to Nov. 5, an average of 7.4 golden eagles flew by every hour.
Golden eagle numbers peaked Oct. 13 when 223 birds were recorded in nine hours.
The Big Belts are a 75-mile long, northwest-to-southeast section of the Rocky Mountains.
When raptors migrate between breeding and wintering grounds, they follow predictable migration routes and concentrate along specific geographic features, especially high mountain ridges and coastlines with optimal flying conditions.
That makes observations possible in popular migration routes like the Big Belts, where strong, prevailing southwesterly winds constantly blow. In combination with the southern Big Belts’ steep, westerly slopes, powerful updrafts are generated, providing ideal flying conditions for migrating raptors.
Bald eagles, several species of hawks and falcons use the Big Belts flyway along with golden eagles.
Some 4,389 migrating raptors of 17 species were recorded during the survey, with an average passage rate of 12.4 raptors an hour.
On Sept. 23, all 17 species of raptors known to migrate through the region were recorded, an unprecedented occurrence in the West, the report says.
The golden eagle was by far the most numerous migrant raptor.
From Oct. 11 and Oct. 15, 1,665 golden eagles were counted, the highest five-day passage rate.
The Big Belt Mountains were first recognized as a significant migration flyway for Golden Eagles in 2007.
In 2015, golden eagles and other raptors were counted for a partial season that did not begin until Sept. 15. Still, 2,630 golden eagles were counted.
The fall 2016 study represents the longest period of daily, standardized raptor migration observation ever conducted in the Big Belt Mountains, the report says.
The purpose of the observations is to study movement patterns of all diurnal raptor species, especially golden eagles, as they pass through Big Belts flyway to assess long-term population trends.
“As the changing global climate is rapidly affecting northern latitudes, monitoring populations of North American Golden Eagles breeding in far northern latitudes (many of which migrate via the Rocky Mountain Flyway) has become increasingly important,” the report says.
It’s not the only site in Montana where golden eagles are counted.
Since 1991, golden eagles have been counted in the Bridger Mountains, which are about 80 miles southeast of the Big Belt Mountains.
This year in the Bridger Mountains, the migration count for all raptors was 3,074, the fifth highest on record, according to a report on the 2016 migration survey by Montana Audubon and HawkWatch International.
That number included 1,329 golden eagles. A previous decline in golden eagles documented at the Bridger Mountain site seems to be reversing, Hoffman said.
“We don’t even know why it declined so it’s really hard to know why it reversed,” Hoffman said.
One would expect the counts of golden eagles in the Big Belts to be similar those in the Bridger Mountains because the Bridger Mountains are only two to three hours of flying time southeast of the Big Belts, Hoffman said. But almost double the number golden eagles are being counted in the Big Belts. Many of the golden eagles seem to be making a sharp turn to the east toward the Crazy Mountains instead of continuing onto the Bridger Mountains.
“Why do they do that?” Hoffman said. “That’s interesting.”
A large increase in turkey vultures has been recorded at the Bridger Mountains over the past five years, the Bridger survey report says. That suggests that the birds may be expanding their range northward in response to a warming climate, the report says.
In past years, turkey vultures have only rarely been documented at the Bridger Mountain observation site, and they’ve been residents, the report says. However, in 2016 a flock of 10 to 12 individuals cruised up and down the ridgeline near the observation point. They also were observed soaring together to the east in the vicinity of the Bangtail Range, the report says.
“These thermal-loving scavengers remained in the area from Aug. 29 to Aug. 30 before disappearing,” the report says.