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.
Since swifts are nearly impossible to locate on the ground and can likely exceed 100 mph in flight, population estimates are sketchy. Even so, it's thought that the species has suffered a relentless decline over the past 40 years. The total population, estimated at 15,000, is thought to be declining about 6 percent a year, Breeding Bird Survey data shows. Deforestation, which may be degrading the birds' Amazon wintering grounds, along with climate change are the biggest threats. In fact, the federal 2010 State of the Birds report, coauthored by Audubon and other conservation groups, rated the species as the western forest bird most vulnerable to climate change. Because it depends on water flow at nesting sites, the predicted loss of glaciers and decreased precipitation could shrink suitable breeding grounds. Climate change might also disturb the flying ant hatch, a major part of the bird's summer diet. Add that the species rears a single, slow-growing nestling, and it's easy to see why this elusive bird is facing serious trouble.
The species was one of the last North American birds described to science, in 1857. Nearly a half-century passed before the first nest was found, in 1901, on a sopping-wet coastal cliff in California. Most of the documented nesting sites are in Colorado, where swift detectives have been most active, though one or more breeding areas have also been found in British Columbia, Alberta, Montana, Idaho, Utah, New Mexico, Arizona, Mexico, Central America, and the Caribbean. Sometimes a decade passes between discoveries. The first site in Oregon was uncovered just this past summer.
In part that's because the wide-ranging birds conceal their young on dripping rock faces behind or near waterfalls and inside caves, making roosts extremely difficult to locate, much less access. To complicate matters, swifts are exceptionally evasive. The tireless aerialists can cover hundreds of miles a day in search of food, spending 10 or 12 hours on the wing often at heights too high for the naked eye to see. And when they return to a nesting site, they might shoot through a curtain of water so quickly that even a careful observer could blink and miss it.
Those under the black swift's spell are "crazy about the birds, and they sometimes go to crazy extremes," says Gunn. Take ornithologist Owen Knorr. As a graduate student in 1949, hoping to solve the mystery of the bird's winter whereabouts, he was the first to band them. To do so he rappelled down the 285-foot-high Box Canon Falls--in the dark--swung under an overhang, and distracted the birds with a flashlight beam while he grabbed them.
From 1949 through 1958 Knorr documented about 80 nests at 27 sites in Colorado. Only six more colonies were discovered in the state in the next half-century. Richard Levad, the Rocky Mountain Bird Observatory's coordinator of special monitoring projects before Beason, got hooked on the birds in the 1990s and didn't think twice about setting off into the wilderness or clambering up slick rock faces in search of them. In 1998, under his guidance, the observatory joined forces with U.S. Forest Service biologists to inventory Colorado's black swifts. To date they've investigated nearly 400 sites.
Thanks to the devotion of the likes of Knorr and Levad (who died in 2010 and 2008, respectively), black swift enthusiasts now recognize the hallmarks of likely nesting sites: water, a lofty position, inaccessibility, darkness, and unobstructed flyways. These days they use mist nets and modified fishing nets with extra-long handles to catch adults, but reaching some nesting sites still requires ropes, ladders, and a sense of adventure.
Close observation of the birds on their breeding grounds has helped paint a general picture. Gunn's soon-to-be published data indicates that nesting sites have extremely narrow temperature and humidity ranges--compounding the threat from climate change. Both the male and female care for the chick. At first they stay close, feeding it periodically during the day. In a couple of weeks, after the chick develops a thick downy coat, the parents start to forage from dawn until dusk, regurgitating insects throughout the night to feed their only child. The hearty meals allow the youngster to nearly match--or even surpass--its parents' size and weight by the time it fledges, at around 48 days, in late August or early September.
Incredibly, it seems that the maiden flight is the first leg of migration. Sue Hirshman has spent 17 years monitoring the swifts in Box Canon Falls, which, with about a dozen breeding pairs, is Colorado's largest known nesting site. In that time she has recorded only one fledgling returning to the nest, for one night during a fierce thunderstorm. "I start in May, and I come every day until the last chick leaves," says Hirshman, a member of Black Canyon Audubon who is so smitten with the birds that she successfully petitioned for the site to become an Important Bird Area. "Every year my friends tease me that I suffer from empty-nest syndrome. I'm going to keep coming to monitor these birds as long as the good Lord lets me."
Researchers still don't know if the birds, which may mate in flight, are monogamous, or if they return to their natal cave to breed. One particularly perplexing mystery is how the chicks survive alone for hours on end, their feathers ever damp; the leading theory is that during the day they go into torpor, a hibernation-like state, to conserve energy and keep warm.