Ardea
Official journal of the Netherlands Ornithologists' Union

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Frank D. & Becker P.H. (1992) Body-mass and nest reliefs in Common Terns Sterna hirundo exposed to different feeding conditions. ARDEA 80 (1): 57-69
In 1984-86, we studied body mass, length of time birds were absent for feeding and nest reliefs in Common Terns Sterna hirundo breeding on the island of Minsener Oldeoog and at Augustgroden (mainland coast), German Wadden Sea. On average, body mass gain per feeding flight was 13.2-15.8 g, and this was negatively correlated with the mass just before departing for feeding. Terns were absent for 1.6-2.7 h per feeding flight. On Minsener Oldeoog, body mass was negatively correlated with wind speed, and the length of time birds were absent for feeding was positively correlated with wind speed. Highest frequency of nest reliefs and highest body mass were recorded during the last four hours before low water, when foraging at sea is most favourable for Common Terns. On Minsener Oldeoog, body mass and length of time birds were absent for feeding were influenced by the length of the daily period that foraging conditions in the Wadden Sea were favourable in 1985. At Augustgroden, the terns showed a trend for higher frequencies of nest reliefs and for shorter lengths of time that the birds were absent for feeding, and they had a lower mass before and after feeding in 1985 than on Minsener Oldeoog. This is because the birds at Augustgroden also foraged on limnetic prey in inland ditches and canals, especially during the flood period and during the period around high water. Both on Minsener Oldeoog and at Augustgroden differences between years were related mainly to variations in food availability.


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