Manx Shearwaters Get Jet-Lagged on Long Ocean Flights, Study Finds

Manx shearwaters flying hundreds of kilometers over the North Atlantic can throw their own internal clocks out of sync, a mismatch that skews the sun-based compass they use to find their way home, according to a study in the journal Science reported by Ars Technica.

The effect works the same way jet lag does in humans crossing time zones, except the shearwater causes it to itself during a single day's flight.

What is a Manx shearwater, and why does it matter for this study?

Manx shearwaters are, in the words of lead author Patrick Lewin, a behavioral and sensory ecologist at the University of Oxford, "medium-sized birds, about the same size as a pigeon" that are "white underneath and black on top" with long wings, closely related to albatross, Lewin told Ars Technica. The birds nest in burrows on coastal islands around the North Atlantic, with most of the population breeding around the UK and Ireland and roughly half living in Wales. From their colonies, shearwaters fly out to feed anywhere from a few dozen kilometers to more than 1,000 kilometers offshore, according to the study.

How does a shearwater find its way back to the colony?

Researchers believe the birds combine two systems: a map sense, possibly based on smell, that tells them roughly where they are, and a sun compass that tells them which direction to fly. The problem, Lewin explained, is that the sun's position in the sky changes constantly through the day. "You can imagine an animal or a human that wants to travel south all day. At sunrise, when the Sun's in the east, it needs to be traveling 90 degrees clockwise of the Sun, but by midday it needs to be traveling straight towards the Sun, and by sunset it needs to be traveling 90 degrees anticlockwise of the Sun," Lewin said. Using the sun as a compass requires an internal clock that tracks time of day accurately — and that clock is where the trouble starts.

Why does a long flight throw the clock off by four minutes a degree?

Shearwaters reset their internal clocks at dawn and dusk, the study found. That daily recalibration works fine for a bird that stays near one longitude. But a bird flying east or west covers ground fast enough that its clock drifts out of step with local solar time — by four minutes for every degree of longitude crossed between sunrise and sunset. Because the clock still thinks it's an earlier or later hour than it actually is locally, the bird misjudges where the sun should be. The result is a consistent steering error: shearwaters veer clockwise off course when flying east and anticlockwise when flying west, according to the findings.

What evidence do researchers have that this happens in the wild?

Scientists had already shown a similar effect by capturing penguins and physically moving them across lines of longitude, forcing a sudden clock mismatch. But no one had demonstrated the phenomenon in wild animals navigating on their own, mainly because the effect is small and detecting it requires a large volume of flight data, the study notes.

That is where a two-decade-old dataset came in. Tim Guilford, Lewin's supervisor at Oxford, and longtime shearwater researcher Chris Perrins began fitting the birds with GPS tags in 2004, as soon as the devices became small enough for a bird that size. By the time Lewin's team analyzed the records, it covered 3,688 foraging trips made by 1,045 birds from colonies along the UK's western coasts, with individual trips lasting anywhere from a single day to two weeks.

When did the tracking data turn into this finding?

• 2004 — Guilford and Perrins begin tagging Manx shearwaters with GPS devices small enough to carry.
• 2004–2024 — The project accumulates tracks from 3,688 foraging trips by 1,045 birds, each trip ranging from one day to two weeks.
• 2026 — Lewin and colleagues analyze the full two-decade dataset and publish findings in Science, showing a measurable, self-inflicted jet-lag effect that steers the birds off course.

What does this mean for how scientists study animal navigation?

The shearwater findings give researchers a documented, real-world example of circadian drift affecting navigation outside the lab, without any human intervention. Because the error scales directly with longitude crossed — four minutes of clock drift per degree — it offers a predictable signature that other studies of long-distance migratory birds could look for in their own tracking data, according to the reported methodology.

For now, the result stands as a narrow but concrete mechanism: a bird's own clock, built to reset at sunrise and sunset, becomes a liability on exactly the kind of marathon flights — some covering more than 1,000 kilometers — that define a shearwater's feeding trips.