Critter Watch: Bridge favors troubled critters
Spokane’s Sunset Highway Bridge is far more than a passageway for motorists across Hangman Creek.
The bridge doubles as a condo for discerning critters.
The architectural designed that makes it pleasing to the eye also has nooks and crannies favored by a variety of nesting birds, including peregrine falcons.
And just last month, a Washington Department of Fish and Wildlife biologist was thrilled to discover a Townsend’s big-eared bat maternity colony.
“It’s just like a cave under there,” said Howard Ferguson, who had teamed with Spokane County bridge maintenance crews to search for the return of peregrine falcons that have been nesting there almost yearly since the late 1990s.
The Townsend’s name owes to ears that are 1.5 inches long — pretty darned big considering the bat’s entire length ranges from 3.5 to 4.5 inches.
The Townsend is a “lump-nosed” bat with large glandular masses like warts between the eyes. Truly a face only a mother could love.
Lava tubes, caves and man-made cave-like structures such as mines are among the Townsend’s favorite habitats for rearing and hibernating. They can fly at very low speeds, almost hovering in flight, to prey on insects, primarily small moths.
This is about the time of year the female bats give birth and tend to their young in the maternity colonies, while the males are off somewhere else, on their own.
Meanwhile, Ferguson said he saw a pair of peregrine falcons copulating near the bridge this spring, but he wasn’t sure at that time whether the birds were nesting, yet.
Spokane’s Sunset Highway bridge, which parallels Interstate-90 and railroad bridges at the junction with U.S. Highway 195, is a standout location for giving chicks a chance to survive, Ferguson said.
Choice peregrine nest sites in Eastern Washington have been found near Palouse Falls, Banks Lake and Coffee Pot Lake. But Spokane stands out as one of the best urban sites.
One female nested under the Sunset bridge for at least seven consecutive years before disappearing two years ago. She was known to have produced 17 chicks in Spokane. Nine were banded.
The bridge spans Hangman Creek, a narrow ribbon of water, just big enough to produce the insects that attract the birds peregrines can hunt, such as the white-throated swifts that nest in the vertical tubes under the I-90 bridge. Yet the bridge is situated in a big gorge with steep banks and a variety of shrubs and trees protected in High Bridge Park.
This combination gives the fledglings a decent chance at surviving the first few unpracticed flights.
Adult peregrines are top guns that can stoop to speeds exceeding 200 mph to prey upon other birds in midair. But peregrine chicks making their first leap from the nest in July often land in a heap on the ground.
That’s the beauty of the High Bridge site. The fledglings are not likely to drown or be hit by a vehicle or snapped up by a dog.
Weak-flying fledglings can easily avoid Hangman Creek. Even if they hit the ground, they can get oriented, walk up a steep bank if necessary and fly into a tree or shrub for more security. Given a chance, the parents will continue to feed the chicks and eventually they can make short hops back up to the bridge or aerie for another shot at flying.
Indeed, many urban sites from Seattle to New York offer fledglings little hope. The birds reared under the popular public eye of video cameras at the Washington Mutual building in Seattle have the safety of ledges and a bounty of food. But when they fledge, they crash into a sidewalk or get hit by a car.
Peregrine falcon numbers plunged throughout the United States shortly after World War II because of the widespread use of the pesticide DDT. The chemical accumulated in the birds peregrine falcons ate, which led to a decrease in falcon reproduction.
Their success is among the shining examples in the recovery of a species that was on the verge of doom 30 years ago.
And the Sunset Bridge has been part of the dawn of their revival.