Foraging-Flock Recruitment at a Black-Billed Gull Colony: Implications for the Information Center Hypothesis

Abstract

The extent to which a flock leader advertises its departure from a colony and recruits flock mates is an important issue of the information center hypothesis. At a colony of black-billed gulls (L. bulleri), attractive calls were given by some leaders, leaders called more often than followers, and calling leaders recruited followers more often than silent leaders. Playback experiments demonstrated that these contact calls were attractive. Some benefits, most likely related to group foraging, result from flock membership when the gulls are away from the colony. Benefits of group foraging away from the colony provide a more likely mechanism for explaining food-related selection pressures favoring a colonial foraging system than the presumed benefits derived from the more complex, information-transfer mechanism envisaged by the information center hypothesis.