Our internal circadian clock regulates daily life processes and is synchronized by external cues, the so-called Zeitgebers. The main cue is the light-dark cycle, whose strength is largely reduced in extreme habitats such as in the Arctic during the polar summer. Using a radiotelemetry system a team of researchers from the Max Planck Institute for Ornithology have now found, in four bird species in Alaska, different daily activity patterns ranging from strictly rhythmic to completely arrhythmic. These differences are attributed to the species' mating systems and behaviours. The study shows that activity patterns can change according to social and environmental factors, which suggests a remarkable plasticity in the avian circadian system.
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