Oxford team links seabirds’ course errors to body-clock lag
Adult Manx shearwaters corrected heading errors of up to about 15 degrees, and researchers estimate that continuous corrections could keep the added journey short.
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Adult Manx shearwaters corrected heading errors of up to about 15 degrees, and researchers estimate that continuous corrections could keep the added journey short.
A University of Oxford team has linked small navigation errors in wild Manx shearwaters to a jet-lag-like mismatch between their body clocks and local solar time. The tracked adults veered off course by up to about 15 degrees, but corrected their routes as they flew home, limiting the effect on their journeys.
Most studies of birds’ biological clocks have taken place in laboratories. Patrick Lewin, a behavioural and sensory ecologist at Oxford, led this investigation using long-term tracking of birds travelling freely at sea.
Manx shearwaters breed on islands off the western coasts of the UK and Ireland. They forage in the Irish Sea and Northeast Atlantic, sometimes reaching feeding grounds about 1,000 km west of their colonies before returning to their nests.
The birds use a time-compensated sun compass: they combine the sun’s position with their internal estimate of the time of day to choose a direction. Because Earth’s rotation makes the sun move across the sky, its position alone does not give a fixed compass bearing.
Sunrise normally helps reset a bird’s body clock. During a rapid eastward return flight, however, a shearwater enters places where sunrise happened earlier. Its clock may then lag behind local solar time by up to around an hour. The sun lies farther around the sky than the bird expects, which can lead it to choose the wrong heading.
The analysis covered 20 years of GPS tracking from 1,045 Manx shearwaters on 3,688 foraging trips. The 2026 Science paper is titled “Rapid longitudinal flights cause time shifts and sun compass error”.
The researchers used statistical models to compare the birds’ actual headings with errors predicted from their movements and the sun’s changing position. Eastbound birds tended to deviate clockwise, as predicted for clocks running behind local time. The sun-compass explanation fitted the observations better than an alternative based on changes in Earth’s magnetic field. The team inferred the clock mismatch from these flight patterns.
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The errors persisted along visible coastlines, where landmarks were available. Birds flew closer to shore when the predicted error pointed towards land and farther offshore when it pointed away. The researchers interpreted this pattern as evidence that the sun compass continued to influence direction rather than the birds simply following the coast.
Analysis
The adults appeared able to reassess their position and adjust their homeward route continuously. To estimate the resulting detour, the researchers calculated a scenario in which a bird started 1,000 km away, maintained an average compass error of 7 degrees and continually corrected its course until it came within 5 km of its colony. That produced about 5 km of additional travel—a calculated distance, not a measured detour or an estimate based on the maximum error.
Lewin suggests a different possibility for first-time migrants. If inexperienced birds lack a map sense—the ability to work out their position and reorient themselves—and cannot continually correct their course, small compass errors could accumulate into deviations of hundreds of kilometres. That is a proposed risk for inexperienced birds, not the observed outcome in the tracked adults.
Professor Richard Holland of Bangor University, who was not involved in the study, told The Guardian that the finding appeared to confirm laboratory evidence that daytime travellers can rely on a sun compass even when it is inaccurate. He said the ecological consequences remained unclear because the errors were small and the birds returned to their colonies.
Lewin proposes investigating how clock mismatch affects behaviour and the way birds’ bodies function. The researchers call for further work to test whether similar effects occur in wild migrating birds and whether they have consequences for health, behaviour or survival.
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