Out of the Shadows: Black Swifts, North America's Most Mysterious Birds

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 Wilson Journal of Ornithology 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 “Unlocking Migration’s Secrets"). 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.