Evidence of social information on food location in a ring-billed gull colony, but the birds do not use it

Bird colonies are potentially rich sources of social information that can be used to compensate for the numerous disadvantages of communal life. This information can reduce uncertainty about nest locations, mates or food sources. However, there is little empirical evidence that colonies can actually serve as an information exchange point. We asked whether a large nesting colony of ring-billed gulls, Larus delawarensis, could provide its members with social information about the quality and location of food resources during the chick-rearing period. We first determined whether social information was available in the colony, then whether it was signalled by some reliable cue, and finally, whether the birds used it by following knowledgeable individuals. We combined observations of flight departure bearings at the colony with flight tracks obtained from birds fitted with global positioning system (GPS) data loggers. We found that reliable information about feeding site locations could be obtained by observing the vanishing bearings of gulls leaving their nest. Birds nesting in different parts of the colony flew in different directions to reach their feeding grounds, but this did not influence the type of food brought to the chicks. To test whether gulls actually followed departing individuals, we searched for temporal clumping of departures and bearings for different time intervals during a day. We found that departures of gulls nesting in the same neighbourhood were not temporally clustered, nor did the gulls tend to leave in the same direction as their previously departing neighbours. We conclude that ring-billed gulls do not appear to use social information at the nest site to locate foraging opportunities. However, stopovers on nearby water or along the colony edge after a short flight from the nest could allow exchange of information that we could not document.

► Reliable information about feeding sites is available in a gull colony. ► Information could be obtained from vanishing bearings of gulls leaving their nest. ► Departures of neighbourhood gulls were not temporally clumped. ► Gulls did not leave in the same direction as their previously departing neighbours. ► We conclude that no information appears to be obtained at the nest site.