Out of the Shadows: Black Swifts, North America's Most Mysterious Birds
Whether exploring dark, wet caves in Colorado or crossing paths with Montana's grizzlies, a dedicated band of scientists and volunteers is determined to solve the mystery of one of the most elusive birds on earth.
On a mid-July evening he and three other volunteers hiked to a spot above Glacier's Avalanche Lake and settled on a boulder with a view of four separate waterfalls cascading off the towering cliffs above the lake. They watched a number of feeding swifts, trying to see if any zipped into the falls. At about 9 p.m. one of them looked away from the birds. "Well, I don't know about you guys," he said, "but I think I'm going to turn around because there's a grizzly bear coming." He pointed to an enormous bear 200 feet away in the brush. "Yeah--we retreated," says Casey.
"Safety is a very real concern, especially with a bird that we're trying to survey primarily with volunteers," Casey says. "So while there are literally hundreds of potential sites in Glacier, we'll never fully inventory all of them. Getting to them will mean bushwhacking through bear-infested forest, hiking around after sundown."
In many ways, Glacier epitomizes the challenges and risks facing not only the people who research black swifts but also the birds themselves. Glaciers that help feed the park's waterfalls may disappear entirely within 20 years. Since a glacier-fed waterfall dried up, at least one colony has already vanished (that doesn't mean the birds died--merely that they're no longer using that site). Elsewhere in the Rockies and Southwest, climate models predict that warmer, drier conditions will cause decreased snowpack and earlier melting, contributing to reduced summer flows. Droughts, like the one that plagued much of the country this summer, are expected to worsen. There's also the possibility that climate could alter the timing of insect hatches, making the swift's food source scarce. "Here we have a bird very reliant on cool, moist habitat," says Casey. "It's the canary in the coal mine where climate change is concerned. We could see it blink out as the effects worsen."
Rather than taking a fatalistic view, that notion spurs Casey and his cohorts to search out new nesting sites. Maybe they'll find that these birds are more resilient than they're thought to be--perhaps direct sun and less moisture isn't as much of a threat to the young, for instance. Casey notes that at one site in Glacier, in direct contrast to conventional wisdom, nests were hit by full sunlight for part of the day. "If we can identify more sites, and get a sense of the variation, we may start to get a picture of how suitable habitat is changing and how the birds are responding."
Back at the Fulton Resurgence Cave in Colorado, the last light drains from the sky. Working by headlamp, Gunn and Beason measure and weigh each adult, taking feather samples and banding those that haven't been captured before. Potter continues trying to catch adults, some of which have stolen past the net. The birds darting around outside the cave emit low, flat twittering chirps. The researchers' anxiety grows; they're hoping to recover a geolocator put on a Fulton bird in 2010.
By 10 p.m. all is quiet and still, save the rushing stream. The trio sits silently in the dark, hoping one last swift sporting a backpack will hit the net. Finally, Potter sighs and says it's time to go.
One at a time the birds captured earlier are set free from the cotton sacks they've been placed in to keep them calm. Like all swift species, they don't perch. Instead they cling to cliff walls with their toes. Potter holds each bird up to the rock face, where it hangs for a moment before dropping, falling until it gathers enough air to take flight. In the dim starlight the swifts are just visible as they swing out away from the cave, then arc back inside.
The bird with the geolocator might have died. Perhaps it went to a yet-undiscovered nesting site. Possibly it's a non-breeder that's taken to the wing for months or years, like its non-breeding European cousins. Or maybe it slipped past the net and is safe within the cave, hiding among the shadows, holding on to its secrets for a little bit longer.
Looks: Torpedo-shaped, about 7 inches long, with relatively short tail and long, narrow, curved wings. Sooty black with a frosting of white on the forehead.
Range: Breeds at widely scattered points from British Columbia south to Costa Rica; also in the West Indies. Recently found wintering in western Brazil.
Habitat: Forages in the air over various habitats, from forest to open country. Nests on damp rocky cliffs, usually behind waterfalls or in sea caves.