The Bird That Gives Itself Jet Lag
A sailor crossing the Atlantic with a cheap pocket watch faces a quiet catastrophe: the watch runs fine, but it no longer agrees with the sky. Every degree of longitude the ship covers, the watch falls four minutes behind or ahead of local noon, and a navigator who trusts it will steer by a Sun that has already moved. Manx shearwaters, it turns out, carry the same flawed watch in their heads. These seabirds nest in burrows on coastal islands around the North Atlantic and fly out to feed anywhere from a few dozen to more than 1,000 kilometers into open ocean. Most breed around the UK and Ireland, with roughly half the population living in Wales. Patrick Lewin, a behavioral and sensory ecologist at the University of Oxford and lead author of the study, describes them plainly: medium-sized birds about the size of a pigeon, white underneath and black on top, but with very long wings, and closely related to albatrosses. [1] The mechanism is simple and unforgiving. The birds recalibrate their internal clock at every dusk and dawn. That reset works perfectly as long as the bird stays put. A shearwater that has flown a long way east will misjudge where the Sun ought to be and veer clockwise off its course; fly west and the error bends anticlockwise. Lewin offers a human-scale picture: an animal wanting to travel south all day must head 90 degrees clockwise of the Sun at sunrise, straight toward it at midday, and 90 degrees anticlockwise of it at sunset. Get the time wrong by an hour and every one of those bearings tilts with it.
The size of the mistake is what makes it remarkable. “About an hour is pretty much the maximum that we observed. Most of these are probably 15-minute, 10-minute time differences,” Lewin says. [1] “For us, that would be pretty imperceptible, but it does still have an effect on their compass orientation that we can detect.” A ten-minute error is nothing a person would notice. For a bird steering by the Sun over an ocean with no landmarks, it is a measurable lean — the nautical equivalent of a watch that loses a few seconds a day and a captain who never checks it against the stars.
Twenty Years of Tags, One Clean Signal
The finding did not come from a clever experiment. It came from patience. Tim Guilford, Lewin’s supervisor at Oxford, and Chris Perrins, a long-time Oxford shearwater researcher, began fitting the birds with GPS tags in 2004, the year the devices first became small enough for an animal this size. Two decades later the team held tracks from 3,688 foraging trips made by 1,045 birds from colonies along the UK’s western coasts, with individual trips lasting from a single day up to two weeks. The effect is small and required a large dataset to become apparent.
Sorting the data was easier than collecting it. Foraging shearwaters make short, wiggly flights between dives, but the homeward leg looks nothing like that. “When they are deciding to go back to their colony, they kind of switch into this mode where they are flying as fast as they can in pretty much a straight line continuously without stopping for really long periods,” Lewin says. From each homing flight the researchers identified where the bird last saw the sunrise, the moment its clock should have matched local time. At every later GPS fix they calculated how far east or west it had traveled since and how much that distance would bend its Sun compass. Because every bird was headed to its own burrow, the predicted deviation could be set directly against the real one. Across 335 homing flights made out of sight of land, the birds veered just as the Sun compass predictions said they would.
The team did not stop at a match. They tested the alternatives — biases that crosswinds, the Coriolis effect, or a magnetic compass might introduce — and none of them fit the data well. “Our observed biases match by far the best to the Sun compass biases that we would expect,” Lewin says. [1] Earlier work had already shown something similar in other birds by catching penguins and quickly moving them across lines of longitude. What was missing was a demonstration in wild animals moving under their own power, and that gap is now closed. The errors reached up to around 15 degrees. For a shearwater flying 1,000 kilometers east in a day — about the maximum the scientists observed — the average error works out to roughly seven degrees, and a bird that keeps checking its position adds only five kilometers to the trip. A crooked line, in other words, that costs almost nothing.
What the Data Cannot Prove
There is a hard ceiling on this result, and it sits in the study’s design. Because the work was not a controlled experiment, Lewin argues for caution about causality: the correlation is strong, the alternatives are weak, but the birds were never assigned to treatments. What the data show is that the observed deviations line up with Sun compass predictions better than with any competing explanation — not that a laboratory-style proof exists.
The coastline data sharpen the puzzle rather than settle it. When shearwaters followed coastlines, they still drifted slightly closer to or farther from the shore depending on their expected compass error. Work done in Oxford two decades ago showed that homing pigeons with shifted clocks do the same, even while following a familiar road. That led researchers to hypothesize two parallel navigation systems, one built on the compass and one on familiar landmarks, with the balance between them never tipping entirely to one side. Lewin offers a second reading: perhaps the birds do not know exactly where on the coast they are and use the Sun to choose which way to follow it. “We don’t quite know. And I think it’s an interesting question, especially as people try and design bio-inspired autonomous navigation systems,” he says.
The study also cannot say whether the birds suffer the rest of what humans call jet lag — poor sleep, hunger at odd hours. “We’ve not been able to investigate that yet,” Lewin says. The next step for his team is to find out whether the time shifts affect when birds forage, how much food they bring home, and their breeding success. A further question is whether more animals routinely experience the effect; Lewin thinks it is quite likely. Any organism with an internal clock that moves far enough east or west in a single day could be hit — mostly fliers, or animals living near the poles, where lines of longitude are packed closer together. The long-term goal is to learn whether animals that live with constant jet lag have evolved ways to cope. “In humans, if you do it a lot, in the long term it has really negative health impacts,” Lewin says. “So maybe we could take some inspiration from these animals that are constantly experiencing jet lag and see if there are ways that we can mitigate jet lag affecting humans.”