Journal Article

Synchronized vigilance while feeding in common eider brood-rearing coalitions

Markus Öst and Tekla Tierala

in Behavioral Ecology

Published on behalf of International Society for Behavioral Ecology

Volume 22, issue 2, pages 378-384
Published in print January 2011 | ISSN: 1045-2249
Published online February 2011 | e-ISSN: 1465-7279 | DOI:
Synchronized vigilance while feeding in common eider brood-rearing coalitions

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  • Evolutionary Biology
  • Ecology and Conservation
  • Zoology and Animal Sciences


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The timing of vigilance and feeding in groups determines the efficiency of shared predator detection and foraging success. Behavioral monitoring of conspecifics remains controversial although synchronization is commonly observed and need not compromise predator detection. The within-group timing of vigilance shows inconsistent associations with group size, and whether nearby nongroup conspecifics affect this timing is poorly understood. Finally, it is unknown whether socially breeding parents time their activities to each other based on offspring predation risk. We studied diving common eider females (Somateria mollissima) in brood-rearing coalitions subject to gull predation of ducklings. The within-group timing of vigilance was determined by comparing observed collective vigilance, the proportion of time during which at least 1 adult group member is vigilant, with that expected assuming independent timing of activities. We determined the predictors of within-group timing of vigilance, observed collective vigilance, individual vigilance, frequency of nearby nongroup females (group outsiders), and incidence of alarm reactions. Vigilance was synchronized regardless of brood composition. Synchronization and observed collective vigilance increased with female group size, whereas synchronization decreased with increasing ratios of ducklings to tending females. Individual vigilance increased in the presence of gull alarms. Within-group timing of activities was unrelated to the presence of group outsiders, but broods with fewer ducklings (less predation dilution) were more often associated with group outsiders, the frequency of which was negatively associated with the incidence of gull alarms. Increased offspring predation risk thus reduces overlapping vigilance among adult group members and enhances attraction to nearby nongroup conspecifics.

Keywords: antipredator behavior; common eider; group living; parental care; risk dilution; synchronization of vigilance

Journal Article.  5263 words.  Illustrated.

Subjects: Evolutionary Biology ; Ecology and Conservation ; Zoology and Animal Sciences

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