Manx shearwaters that fly long distances over the North Atlantic experience a form of jet lag that skews their navigation, according to a new study in Science. Lead author Patrick Lewin, a behavioral and sensory ecologist at the University of Oxford, said the birds use the Sun as a compass. Their internal clocks fall out of sync with local time as they travel east or west, which shifts their sense of where the Sun should be.
The team analyzed GPS tracks from 3,688 foraging trips by 1,045 birds from colonies along the UK's western coasts. The researchers focused on 335 homing flights made out of sight of land. Lewin said the birds veered in the direction the Sun-compass model predicted. The clock shift was small, with most differences around 10 to 15 minutes, and the observed course errors reached up to about 15 degrees.
Lewin said the study is observational rather than a controlled experiment, so causality needs careful interpretation. The team also tested crosswinds, the Coriolis effect and a magnetic compass as possible causes. Lewin said none fit the data as well as the Sun-compass explanation.
According to Lewin's calculations, a shearwater flying 1,000 kilometers east in a day would have an average error of about seven degrees. If the bird checks its position and corrects, the extra distance would be about five kilometers.