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1 December 2008 Diurnal and Nocturnal Feeding Strategies in Common Eiders
Flemming Ravn Merke, Anders Mosbech
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Feeding activity of wintering Common Eiders (Somateria mollissima) was conducted in Southwest Greenland. Behavioral observations were made at two wintering sites, a fjord habitat and an outer coastal habitat, at which habitat characteristics and human activities differed considerably. In the coastal area where hunting and fishing was common and foraging typically occurred 0.5 to one km from the shore eiders were identified as primarily diurnal feeders. They also foraged during twilight periods, but only rarely at night. In contrast, in the fjord where human disturbance was rare and foraging occurred very close to the shore (<50 m) adult eiders fed only during twilight and at night. During daytime, birds gathered in large communal roosts in open water away from feeding areas. Occasionally, feeding was initiated by juveniles during daytime, but was discontinued due to interactions with White-tailed Eagles (Haliaeetus albicilla groenlandicus) and suggests that nocturnal feeding is an anti-predator mechanism. More experienced adult birds in the fjord did not attempt feeding during daylight hours. Large communal roosts observed at deep waters during previous aerial surveys suggest that nocturnal feeding maybe common throughout the fjords in Southwest Greenland.

Flemming Ravn Merke and Anders Mosbech "Diurnal and Nocturnal Feeding Strategies in Common Eiders," Waterbirds 31(4), 580-586, (1 December 2008).
Received: 10 January 2007; Accepted: 1 April 2007; Published: 1 December 2008

-anti-predator response
Common Eider
diurnal feeding
nocturnal feeding
Somateria mollissima
Southwest Greenland
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