Diel and seasonal rhythmicity in activity and corticosterone in an Arctic migratory herbivore: A multifaceted approach

Birds that migrate from temperate areas to the Arctic for breeding lose their strongest Zeitgeber of circadian organization when they cross the Arctic circle in spring — the 24h geophysical light-dark cycle. Under continuous daylight various behavioural and physiological patterns have been detected in both free-ranging and laboratory animals. To better understand the evolution of plasticity in circadian clocks, it is essential to study behavioural and physiological rhythmicity in the context of a species' ecology. Employing a multifaceted approach, which included wildlife cameras, accelerometers, and non-invasive sampling of hormone metabolites, we investigated activity patterns and corticosterone rhythmicity in a migratory herbivore, the Svalbard barnacle goose (Branta leucopsis), during its Arctic breeding season. We detected that females showed a combination of both ultradian and diel rhythmicity in incubation recesses and sleep, respectively. In both parents, rhythms in activity continued over the period, when goslings were present. During moult, many geese aligned activity with the tidal rhythm. Barnacle geese showed weak diel rhythmicity in excreted corticosterone metabolites. This suggests that while Arctic geese may adopt an alternative Zeitgeber during the Arctic summer to keep a diel rhythm, ultradian rhythmicity is crucial and geese are able to tune their rhythms flexibly to environmental conditions.