Mean vigilance versus flock size in Double-crested Cormorants Phalacrocorax auritus.

Abstract

Social living consists of costs and benefits. Ideally, an organism in a group situation will seek to maximize its benefits while minimizing its costs. One behavior that should be dependent on group size is vigilance time. Vigilance time is time spent above water watching and/or listening for danger. Time spent vigilant cannot be used to perform reproductively beneficial activities. This study of Double-crested cormorants compares individual mean vigilance times as a function of flock size. Using an ANOVA (p<0.00001 df=58), I detected a significant difference as predicted; vigilance time decreased as flocks ize increased. Therefore, Double-crested Cormorants benefit from decreased individual vigilance time as flock size increases.