Scientists were able to capture never-before-recorded data on the behaviour of the elusive American black swift bird. Among other things, they confirmed that the birds spend nearly all their time flying when not breeding and that they likely rely on moonlight to help them hunt. The team also managed to record them right in the middle of a lunar eclipse, during which time the birds abruptly dove toward Earth.
Black swifts (Cypseloides niger) are considered some of the most mysterious birds around. They’re rarely spotted on the ground, though they do set up nests along the waterfalls and caves of the Western U.S. and Canada. It’s only recently that we’ve started to learn a bit more about their life cycle. About a decade ago, for instance, researchers discovered that some black swift populations migrated as far south as Brazil during the winter, having travelled about 6,437 km from their breeding grounds in Colorado.
One of the scientists behind that study, Rob Sparks, and others went on to found the Black Swift Movement Ecology project, in hopes of further unravelling the secrets of the bird. At a scientific conference, Sparks met Anders Hedenstrom, a fellow bird flight researcher from Sweden. Hedenstrom and his own team had previously found evidence that a related species living in Europe and Africa, the common swift, were aerial roosters, meaning that they seldom left the air while not breeding, spending up to 10 months out of the year in flight. The pair decided to collaborate and see if the same was true for black swifts.
To do this, they carefully captured a few swifts at a site in Colorado using a mist net, then attached backpack harnesses that logged their flight data once in the air. And as before, these loggers provided all sorts of insights into these birds.
“In our study, we confirmed that the black swift flies non-stop over the Amazon during the non-breeding season without landing, roosting in the air akin to their Old-World swift counterparts,” Sparks, a research biologist at the Bird Conservancy of the Rockies, told Gizmodo in an email. For these birds, that time spent airborne amounts to about 8 months out of the year.
The team also found that the swifts seemed to rely on moonlight to help them hunt for the small insects they feed on. During the 10 days around a full moon, the birds consistently ascended higher than usual, up to 4,000 meters. Perhaps most extraordinary, and without meaning to do so, the team also managed to record them during a lunar eclipse. Just as the birds flew high when light was around, they suddenly dropped in altitude when the eclipse hit.
Eclipses tend to get blamed for radical changes in human behaviour, to the point of driving some people mad. But despite the abrupt downward dive, the researchers don’t think that the birds were in any sense frightened by the eclipse.
“These birds are masters of flight and have evolved this wonderful aerial lifestyle, allowing them to adapt to many conditions both diurnal and nocturnal,” Sparks noted.
The flight patterns of these birds during the full moon and the eclipse do seem to highlight the importance of moonlight to them. And the team hopes their findings will further illuminate their mysterious lives. It’s a goal that’s all the more important, since it’s suspected that black swifts have been declining in population over the years.
“The black swift is a rather scarce species of conservation concern in North America, and investigating its entire annual cycle may help making appropriate decisions, should they be needed,” Hedenstrom, a researcher at Lund University, told Gizmodo.
Simply better understanding the lives of these incredible and enigmatic birds is worthwhile on its own, Sparks added. “We hope this increases an appreciation for our natural world and allows us to consider the value of all life on earth,” he said.
Sparks and his team next plan to study how black swifts forage for food during the breeding season and to come up with a reliable way to track their population numbers. Hedenstrom and his colleagues are also studying the behaviour of other nocturnal birds across the Atlantic.