Long ocean flights give seabirds a kind of jet lag, study finds

Seabirds that fly long distances rapidly across lines of longitude can develop a mismatch between their internal clock and the local time at their destination, producing measurable errors in the sun-compass navigation they rely on to find their way home, according to a study published Thursday in the journal Science. The effect, the researchers say, closely resembles the jet lag experienced by long-haul human travelers.

The study, led by researchers in the Department of Biology at the University of Oxford, is based on 20 years of GPS tracking data from Manx shearwaters, a seabird that breeds in large colonies on islands off the coasts of Britain and Ireland, including Skomer Island in Wales. It is among the first studies to show, in a wild animal going about its ordinary life, that the simple act of flying fast enough across time zones can throw off the biological mechanism the animal uses to navigate.

A compass thrown off by speed

Manx shearwaters forage for fish and other prey as far as roughly 1,000 kilometers west of their breeding colonies, often completing the round trip within a few days. Researchers analyzed 3,688 of these foraging trips made by 1,045 birds and found that when the birds flew rapidly westward or eastward across longitude lines, their internal circadian clocks could lag behind local solar time by up to about an hour by the time they needed to navigate home.

That lag matters because Manx shearwaters, like many migratory birds, rely on what biologists call a time-compensated sun compass: an internal mechanism that reads the sun's position in the sky and uses the bird's own sense of time of day to convert that position into a compass bearing. If the internal clock is out of step with the sun's actual position relative to the local horizon, the bearing the bird calculates will be systematically off, even though the bird is using exactly the same method it always has.

The researchers found that shearwaters returning from rapid eastward flights consistently veered in the clockwise direction predicted by a lagging internal clock, with directional errors reaching roughly 15 degrees. A model built around sun-compass errors fit the observed flight paths better than a model based on disturbances to Earth's magnetic field, which some seabirds also use as a navigational cue.

Errors that persist even within sight of land

One of the more striking findings was that the navigational errors did not disappear once birds came within sight of the coast, where landmarks might be expected to override a faulty internal compass. Instead, the birds' paths shifted closer to shore when the predicted sun-compass error pointed them toward land, and further out to sea when the error pointed away from it, as though they were still following the same miscalibrated compass and only partially correcting for it as landmarks became available.

In practical terms, the cost of the error appears to be modest for adult shearwaters making routine foraging trips. The study's authors calculated that a bird returning home from 1,000 kilometers away with a typical seven-degree compass error, while continuously adjusting its course as it approached the colony, would end up flying only about five kilometers farther than a bird with no error at all, close enough to make landfall within five kilometers of its destination.

The bigger concern, the researchers write, is for birds that cannot continuously correct their course the way an experienced adult flying a familiar route can. A young shearwater making its first long migratory flight, without the benefit of prior experience or familiar landmarks, could in principle accumulate a much larger positional error over a long journey, potentially missing its intended destination by a significant margin.

Why the sun compass is so widely used

Time-compensated sun compasses are not unique to shearwaters. Versions of the mechanism have been documented across a wide range of migratory animals, from songbirds to monarch butterflies, making it one of the most common navigational tools in the animal kingdom. Oxford researchers had previously shown, in a 2018 study that artificially shifted shearwaters' internal clocks at their nests, that the birds do rely on this sun-compass mechanism when finding their way home after being released far from their colony.

What the new study adds is evidence that birds can desynchronize their own internal clocks simply by flying fast enough across longitude in the course of normal behavior, without any experimental manipulation by researchers. That distinction matters because it suggests jet lag-like effects are not an artifact of laboratory clock-shifting experiments but a naturally occurring consequence of how far and how fast these animals travel.

"It's amazing to think that billions of migratory animals look up to the sun for direction," said Patrick Lewin, the study's lead researcher at Oxford's Department of Biology. "Our results show that animals experience the same internal clock mismatch as we do during jet lag."

Tim Guilford, a professor in the same department and a co-author of the study, said the finding reflects how difficult it has historically been to study navigation and cognition in wild animals under natural conditions, as opposed to in a laboratory setting. "It's inherently difficult to study the cognitive processes of animals in the wild," Guilford said, according to the university's announcement of the findings, which credited two decades of tracking data for making the analysis possible.

What researchers want to learn next

The authors are careful to describe their findings as evidence consistent with a sun-compass explanation rather than direct proof of the underlying mechanism, since the study relies on statistical modeling of GPS tracks rather than controlled manipulation of the birds' internal clocks in the wild. The analysis also covers a single species, and the researchers caution that the results may not generalize to every migratory bird that uses a sun compass.

Left unanswered, for now, is what the recurring mismatch means for the shearwaters' broader health, behavior and reproductive success, questions the authors flag as priorities for future work, much as sustained jet lag has been linked to disrupted sleep and metabolism in humans. Coverage of the study noted that the researchers see the biggest open question as whether repeated clock mismatches, even small ones, carry a cumulative cost across a shearwater's lifetime of ocean-crossing journeys.

The findings arrive as migratory species worldwide face pressure to travel farther or on altered schedules amid shifting food availability and changing climate conditions, a context that has sharpened scientific interest in how finely tuned animal navigation systems are and how much disruption they can tolerate. Independent summaries of the paper, including from Science News and other science outlets, framed the result as a rare, real-world demonstration that even animals exquisitely adapted to long-distance travel are not immune to the kind of internal clock disruption long associated with human air travel.

For now, the Oxford team says its priority is extending the analysis to other seabird species that rely on sun compasses and to younger, less experienced birds making their first migratory journeys, where the costs of a miscalibrated internal clock may prove far steeper than the modest detours recorded among adult shearwaters on routine foraging trips.