Talk about a long flight. The Alpine swift (Tachymarptis melba) can remain on the wing for more than 6 months, a new study suggests. These 20-centimeter-long, insect-eating birds breed in mountains ranging from southern Europe to the Himalayas. In 2011, researchers strapped tiny instrument packages on six swifts to track their activity during their winter migration to western Africa.
Those instruments measured the intensity of light (which, by detecting sunrise and sunset, allowed researchers to infer each bird’s latitude and longitude) and used accelerometers to gauge the animals’ activity level during a 3.2-second window every 4 minutes, day or night. The team recovered three of the sensor-laden swifts in spring 2012, when the birds returned to Europe for the nesting season.
Analyses revealed that the swifts never settled to roost while in Africa, not even to rest after their 2000-kilometer migration, the researchers report today in Nature Communications. At night, even though the birds' body position didn't change very much, their activity level suggested they were gliding, not resting on a perch—which strongly suggests that the birds were catching a bit of shuteye while aloft.
During the course of their African jaunt, and as much as 200 days spent aloft, the birds likely flew a total of 10,000 kilometers, the researchers estimate. Stretched into a straight line, that distance is about one-fourth of the way around Earth’s equator.
ScienceNOW, the daily online news service of the journal Science
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