Merrit Kennedy at NPR:
Scientists have long suspected that the common swift remains airborne for extraordinary amounts of time during its annual migration.
Now, a team of scientists in Sweden has proved that these birds fly for tremendously long periods of time. They affixed data loggers onto a total of 19 of the master fliers in 2013 and 2014, and recaptured the birds months or years later. Researchers found that the birds can spend almost their entire 10-month nonbreeding period on the wing.
The data loggers gathered information on acceleration and flight activity, and those installed in 2014 also included light trackers for geolocation.
The results were astonishing. For example, according to research published in Current Biology, one of the birds stopped for just four nights in February in 2014 — and the next year it stopped for only two hours. Other birds stopped for longer periods of time. But “even when swifts settle to roost,” the researchers say, “the amount of time not flying is very small.”
The birds are known to travel from Europe to sub-Saharan Africa — but they apparently don't touch down there, as National Geographic reports. Researchers say they have never found roosting sites in sub-Saharan Africa.