Even Birds Get Jet Lag, And It Can Throw Them Off Course

Finding your way home over the open Atlantic takes an extraordinary sense of direction. For Manx shearwaters, it also takes a sense of time. Researchers have found that these seabirds can experience a form of jet lag during long flights, leaving their internal clocks out of step with the sun they use to navigate. The mismatch shows up in small, predictable errors in the direction they fly.

The Oxford-led study, published in Science on October 29, draws on 20 years of GPS tracking involving 1,045 birds. Manx shearwaters breed on islands off the western coasts of Britain and Ireland, sometimes traveling roughly 1,000 kilometers, or 620 miles, west to find food. The return journey gives scientists a chance to study how an animal navigates toward a particular place while surrounded by open water.

The sun compass

The sun can offer a bird information about direction, but its position changes as the day passes. A bird needs an internal estimate of the time to account for that movement and interpret what the sky is telling it. Reading the sun with the wrong time can produce the wrong heading, even when the bird is following a system that usually serves it well.

For the analysis, the researchers calculated the errors they would expect if a bird's clock remained synchronized to the place where it experienced sunrise. As the bird travels east, local solar time moves ahead of that earlier setting. Its body clock can lag behind. The team's tracking data and calculations showed navigation errors consistent with that mismatch. The birds' movements were revealing something about the timekeeping inside them that a GPS tracker cannot measure directly.

If you have ever crossed time zones and found yourself ready for sleep while the day outside was still unfolding, the underlying mismatch may sound familiar. Your surroundings have changed faster than your body has adjusted. For a bird consulting the sun, being out of sync can affect its sense of which direction to take. This is about the changing solar time along its route; a bird never has to cross a boundary on a time-zone map.

The journey home

Even a visible coastline did not erase the pattern. The shearwaters flew closer to shore or farther out to sea in the directions predicted by the clock errors. That suggests they kept using their sun compass when landmarks were available, combining information about the coast with information from the sky.

The errors were relatively small, reaching about 15 degrees. The Zoological Society of London, whose researchers contributed to the study, explains that the birds can correct their routes. In one calculation, a bird returning from 1,000 kilometers away with an average seven-degree compass error would add only about five kilometers before getting within five kilometers of its colony, if it kept correcting its course. That is a modeled example, rather than an average detour measured across the study.

Whether this clock mismatch also disrupts the birds' sleep, feeding, or health remains an open research question. For now, the finding makes their journeys more remarkable to consider: a bird can keep adjusting its way home while its own sense of time is a little behind the sky.