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As the sun sinks into the sky on a warm August evening, a black swift nimbly plucks flying ants out of the air. The balloon-like bolus at her neck bulges with the insects, which she’ll soon feed to her hungry chick hidden away in a mountain cave. Her scythe-like wings and torpedo-shaped body blink in and out of view as she rockets toward a 1,500-foot-deep canyon here in western Colorado’s Flat Tops region, where 10,000-foot-high plateaus are riddled with water-carved caves. She’s heading for one of them: Fulton Resurgence Cave, a teardrop-shaped cavity high on a cliff. Water pours from its mouth, bathing the vibrant green moss and algae growing on the walls in mist as the stream cascades into a steep gulch. It’s the sort of place only spelunkers—or possibly hard-core birders in search of the continent’s most mysterious avian species—would venture. 

The swift makes a tight circle before zipping inside, where her downy chick waits in the dark on a teacup-sized moss nest built on a narrow ledge high above the cave floor. Four more ravenous chicks sit in nests on their own ledges in other parts of the cool, wet cave. The soothing sound of the rushing stream fills the air. These only children—black swifts, unlike the three other North American swift species, lay just one egg—are all safely out of the reach of predators.

Tonight, however, the mother doesn’t make it inside. Instead she’s snagged in a mist net strung across the opening.

“Oh, our first adult!” exclaims Kim Potter, a biologist with the U.S. Forest Service’s White River National Forest. Her short silver hair pokes out from beneath a rock-climbing helmet, and her black fleece jacket wards off the cool air flowing from the cave. 

Since 1998 Potter has made the arduous trek here once a year to monitor the birds. Her intrepid partners include Carolyn Gunn, a Colorado Parks and Wildlife veterinarian who volunteers on the swift project, and Jason Beason, the ’s special monitoring projects coordinator. Also along for the adventure is local photographer Todd Patrick, who has taken hundreds of pictures of the birds and researchers during the past several years. To reach the cave, the group hiked for three hours, losing 2,000 feet in elevation over three miles before covering the final 150-foot drop along a scree-covered slope to the cave hidden below. They’ll make the even more grueling return trip in the dark, using headlamps to follow their trail. 

This afternoon they banded the chicks, using an 18-foot ladder they keep stashed nearby to reach the lofty dwellings. Now it’s 7 p.m., and the adults are beginning to return. “From dusk to dark it’s pretty much rush hour,” says Potter. She jumps up, nimbly crosses the jagged rocks like the long-distance trail runner she is, and disentangles the bird in a few seconds. While she and Gunn examine the swift, Beason crouches near the net, watching for the next captive. 

“She’s nice and healthy-looking,” Potter says, blowing on the bird’s belly to ruffle the feathers and expose a visible layer of fat. Lustrous gray-black body feathers fade to light gray on the face. She has enormous black eyes and a petite nub of a beak. Her curved wings measure 6.5 inches each, and, at an ounce and a half, she’s astonishingly light. Referencing the leg band against a log—ID number 096103486—Gunn gives a little squeal. This female, which they’ve captured here yearly since 2008, helped solve the mystery of one of the bird world’s greatest vanishing acts: where black swifts disappear to in winter. In 2010, for the first time ever, the researchers tracked this and two other birds’ incredible 8,600-mile round-trip journey to lowland rainforest in northwestern Brazil—a country where the species had never before been documented. “These birds are just incredible, absolutely the coolest, most mysterious birds,” says Potter. “For every question we answer, 10 more pop up. There’s so much we don’t know, and we can’t really know how to protect them until we better understand them.”

The clock is ticking as a small but passionate cadre of professional and citizen scientists race to uncover the black swift’s secrets. Throughout the West these researchers are hiking to remote waterfalls and caves, bushwhacking through grizzly country, and scaling slippery cliffs in search of more nesting sites (only about 200 have been documented). At the same time, they’re employing cutting-edge genetic tools and strapping tiny geolocators on the birds to shed light on such basic questions as whether all black swifts winter in the same area and if different colonies mix.

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, 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 Լ����Ƶ 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 Cañon 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 Cañon 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 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.

Then there’s the enigma of their behavior in their wintering grounds. While the three birds from two sites in Colorado outfitted with geolocators all traveled to the same general area in Brazil, no one knows if it’s the primary overwintering site for the global population, or just one of many. Other questions include what they eat down south and where they roost—or if they roost. “Common swifts from Europe fly all winter without roosting at all,” says Beason, explaining that the birds rest in flight. “It’s possible that black swifts could be doing that, or roosting every few days.” 

The Colorado team is turning to technology to solve some of these riddles. They’re putting geolocators—simple gadgets with a light sensor, a digital clock, and a tiny memory chip—on birds from other colonies to chart their migratory routes. The swifts carry them in a special harness Gunn designed and made. Geolocators provide enough information to determine the bird’s location, but researchers must recapture the birds to retrieve the data. So far they’ve recovered four of eight geolocators they’ve deployed. 

“Geolocators don’t pinpoint the exact spot the birds went to, but they do give the general area,” says Beason, lead author of the study published in the in March. “I was most surprised because I thought they’d go to a mountainous area, and it looks like it’s lowland rainforests, though there are some waterfalls and cliffs.” 

This past summer researchers planned to attach geolocators to swifts in New Mexico; next summer they’ll outfit birds in Idaho and California. “We want to determine if other populations of black swifts are all wintering in the same area of Brazil or not,” says Gunn. “If they are, and anything happened to that one spot, it could have huge implications for the breeding population of swifts in North America.”  

Alarmingly, the Amazon is rapidly being cleared for agriculture. One computer model predicts that by 2050 up to 30 percent of the forest cover in the part of Brazil where the birds winter could be lost. Beason and his colleagues are talking with a researcher in South America, hoping that the recent findings will spur studies of black swifts there. Once conservationists know where the birds are going and how they’re using the landscape, they’ll have the ammunition they need to better protect them. For instance, if huge numbers of swifts congregate in one area in winter, conservationists could fight to protect that critical habitat.

The team is already making plans to equip the birds with satellite tags, which will reveal precise migration routes and wintering grounds (see “"). Unfortunately, the current transmitters are too big for swifts, though the Colorado team expects smaller devices will be available in two or three years. They’ll divulge not only the birds’ path but also offer insight into the their behavior—where they stop during their three-week journey to the Amazon and how much time they spend aloft or roosting once they arrive.

Meanwhile, Gunn is spearheading cutting-edge genetic analysis that will give a clearer picture of the population size and diversity. Team members have already collected blood samples from three dozen swifts, and they gathered feathers from birds throughout the breeding range this year. DNA samples allow scientists to decipher how diverse the populations are. “If there’s a lot of gene flow from colony to colony across North America, the birds would be experiencing great genetic diversity,” says Gunn. “They’d have a larger gene pool to draw from and perhaps be more adaptable to risks, like climate change or disease.”

She hopes the analysis will also provide a more accurate population estimate. “Banding and searching for new colonies to add to the count could take decades,” says Gunn. “This should give us a much better population estimate, which directly relates to conservation.”

While the Colorado team forges ahead on the technology front, groups in other states are scouring the wilderness for new nesting sites. In Montana, where three active swift sites are known, that means risking the occasional run-in with a deadly predator, as Daniel Casey discovered in 2004. 

That year Casey, an biologist who lives south of , spearheaded a statewide effort to visit 32 potential nesting sites—places where swifts had been spotted flying above waterfalls or areas that would seem to offer ideal habitat. (They’re still at it; in addition to investigating a variety of potential sites in Glacier, this past summer and scientists and volunteers sought out possible sites elsewhere in the state.) 

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.

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Incredible Journeys

Black Swift

Cypseloides niger

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.

Behavior: Spends most waking hours in continuous flight, like other swifts, catching insects in midair. Travels singly or in small flocks.

Status: Localized and uncommon throughout its range. Total population may not exceed about 20,000 birds. Scattered distribution makes it hard to census.

Threats: Because birds often nest behind waterfalls, destruction of mountain forests or the effects of a drying climate could make some sites unsuitable by reducing stream flows. Deforestation in South America also could degrade their wintering habitat.

Outlook: With its wide range, the species is in no immediate danger, but its long-term survival could be jeopardized by climate change and habitat loss.

This story originally ran in the September-October 2012 issue of Լ����Ƶ as "Out of the Shadows." To receive our print magazine,