Ardea
Official journal of the Netherlands Ornithologists' Union

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Skipnes K. (1983) Incubation behaviour of the Arctic Tern Sterna paradisaea, in relation to time of day and stage of incubation. ARDEA 71 (2): 211-215
Arctic Terns Sterna paradisaea, breeding at 63ŽN in Norway, were studied during June-July 1979. Their daily activity patterns during the laying and incubation periods were similar. The proportion of birds observed asleep was greatest during the day and least in the evening, while the proportion of birds engaged in 'quiet incubation' changed in a directly inverse manner. The frequencies of the 'egg-shifting', 're-settling', and 'nest-building' behaviour patterns did not change during the day. The frequency of 'nest-reliefs' was higher during the day than in the evening. Less time was spent on nest in the middle of the day than in either the morning or the evening. The proportion of time spent 'on nest' (on average 98.8%) did not change significantly during the incubation period. The frequency of birds observed 'outside the nest' (but within the territory), and the proportion of birds asleep, both decreased significantly during the incubation period. The proportion of 'on-duty' birds outside the territory was lowest at the beginning of the incubation period.


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