Shearwaters drift slightly off course when their internal clock falls behind the sun
Twenty years of GPS data from more than a thousand seabirds show that rapid flights across lines of longitude throw off their sun compass, according to a University of Oxford study.
Seabirds that fly quickly from west to east can suffer a kind of jet lag that pushes them off their route. That is the finding of University of Oxford research on the Manx shearwater, published on Thursday in the journal Science, The Guardian and US public broadcaster NPR report. According to the EurekAlert news service, the researchers analysed GPS data from 1,045 wild birds. The Guardian writes that the measurements span twenty years.
Shearwaters spend most of their lives at sea and breed each year in burrows on islands off the west coast of Britain. While one partner incubates the egg, the other forages for up to two weeks, often hundreds of kilometres away over the Atlantic, NPR explains. To find their way back, the birds use the sun as a compass. That only works if their internal clock knows what time it is, because the sun shifts across the sky during the day. Sunrise and sunset normally keep that clock in step with local time.
On the rapid flight back east, the birds' internal clock ran up to about an hour behind local time, lead researcher Patrick Lewin tells The Guardian. As a result they misjudged the sun's position and deviated in a predictable way, by at most about fifteen degrees according to the Guardian. The study says the deviations fit errors in the sun compass better than changes in the Earth's magnetic field. Strikingly, the error also occurred when the birds followed a coastline that could have guided them.
For adult birds the consequences are small, because they correct their course along the way: Lewin calculates about five extra kilometres on a journey of a thousand kilometres. Young birds migrating for the first time, however, could stray hundreds of kilometres off course, he says, because they do not yet have an internal map to reorient themselves. A British biologist not involved in the study tells The Guardian that the research confirms in wild animals what controlled experiments had already shown. According to EurekAlert, the same phenomenon may also affect other migratory animals that cross longitudes quickly.