Body-clock shifts may alter Manx shearwaters’ flight directions
The story at a glance
Researchers analysed 20 years of GPS data from 1,045 breeding Manx shearwaters, covering 3,688 foraging trips. During rapid eastward journeys home, the birds’ flight directions deviated in patterns consistent with their internal clocks lagging behind local solar time. 1
The findings fit an explanation in which a mismatch between a bird’s body clock and local solar time affects its sun-compass navigation. For the tracked birds, the estimated extra distance was modest if they continually corrected course. The analysis did not establish whether the deviations cause harm. 124
What you need to know
- The study examined homing movements by breeding Manx shearwaters, using a large collection of GPS tracks gathered over two decades. Its results concern these tracked birds and should not be taken as a direct measure of navigation by all shearwaters. 1
- Observed flight directions varied in a way predicted if the birds’ internal clocks lagged behind local solar time as they travelled east. This supports the sun-compass explanation, but the tracking analysis did not experimentally manipulate clock timing to demonstrate that mismatch caused each deviation. 1
- The researchers estimated that continuous course correction would add about 5 km to a 1,000 km return journey. The reported deviations for tracked birds were relatively small, and this estimate is not evidence of a measured cost to the birds. 14
- Potentially greater effects on young or first-time migrants remain a possibility, not a finding demonstrated by the adult tracking data. Independent reporting also cautions that further work is needed to establish consequences for behaviour, health or survival. 12
- The research identifies questions beyond flight direction, including whether birds use other navigation cues to correct errors and whether clock shifts affect feeding or resting. The available reports do not resolve these questions. 12
Why this matters
The findings add evidence about how internal timing may relate to seabird navigation during rapid travel. But the estimated route effect is modest for the tracked birds, and the study does not show that it affects their welfare or survival. Distinguishing a detectable directional deviation from a biological cost is important when interpreting the result. 124
What happens next
Further research is needed to test whether less experienced birds face larger or less correctable errors, and whether clock shifts affect behaviour, health or survival. The supplied reports also identify the use of other navigation cues as an open question. 12
What we know
- The analysis covered 1,045 breeding Manx shearwaters and 3,688 foraging trips, using 20 years of GPS data. 1
- The directional deviations during rapid eastward homing flights were consistent with internal clocks lagging behind local solar time. 1
- The observed pattern matched predictions for sun-compass navigation, while the analysis did not directly demonstrate causation through experimental manipulation. 1
- With continuous course correction, the estimated additional distance was about 5 km on a 1,000 km return journey. 14
What we don't know
- The study does not establish whether the directional deviations cause harm to the tracked birds. 12
- It remains unknown whether young or first-time migrants experience larger errors, or whether those errors are harder to correct. 12
- The available reporting does not determine whether clock shifts affect feeding, resting, health or survival. 12
- How often shearwaters use other navigational cues to correct sun-compass errors is unresolved. 1
Read the reporting
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