Rapid travel across longitudes can induce a form of "jet lag" in wild seabirds, leading them to veer off course as they navigate by the Sun, even when alternative navigational cues are available. Animals rely on compass cues, including Earth's magnetic field, stars, and the Sun, to maintain their direction while navigating. To use the Sun as a reliable guide, these creatures must compensate for its movement across the sky using an internal biological clock calibrated primarily by the daily light-dark cycle. When animals travel east or west across lines of longitude, their internal clocks can fall out of sync with local solar time, potentially causing predictable errors in navigation. For example, eastward travel is expected to produce a clockwise deviation from the intended direction, while westward travel should cause a counterclockwise deviation. Although studies of some Arctic migratory birds have supported these expectations, confirming that such deviations result from internal clock shifts requires ruling out other sources of navigational error, particularly changes in Earth's magnetic field.
Here, Patrick Lewin and colleagues analyzed GPS tracking data from 1,045 wild Manx shearwater birds (Puffinus puffinus) to investigate whether rapid east/west travel across longitudes directly disrupts birds' internal clocks and causes errors in Sun-compass navigation. These birds routinely travel upwards of 1,000 kilometers between feeding grounds in the Northeast Atlantic and breeding colonies in the United Kingdom. Lewin et al. found that the birds' navigation became predictably skewed when rapid eastward or westward travel disrupted the alignment between their internal clocks and local solar time. The directional deviations closely matched those expected from errors in their Sun compass, suggesting they rely heavily on the Sun to navigate when out of sight of land. These patterns were more consistent with Sun-compass errors than with errors caused by changes in Earth's magnetic field. Surprisingly, the shearwaters continued using the Sun compass even when they could use alternative navigational cues like following coastlines.
