A TEST OF THE INFORMATION-CENTER HYPOTHESIS IN A COLONY OF SANDWICH TERNS STERNA-SANDVICENSIS

It has been suggested that colonies of terns function as information centres from which unsuccessful foragers follow other birds to feeding sites. From a sandwich tern colony in south-western Sweden, foragers departed in temporal synchrony and birds leaving at the same time headed preferentially in similar directions. However, unsuccessful foragers did not follow other birds from the colony, and successful birds were not followed more often than other birds. Moreover, a 'leader' and a 'follower' that departed together in the same direction flew to the same feeding site in fewer cases than predicted by the hypothesis. A food shortage was noted twice, but there was no indication that terns sought information within the colony during these periods. Thus, clumped departures are weak evidence for the informationcentre hypothesis and in the present case might be explained by clumped arrivals or, possibly, benefits of local enhancement in the foraging area. Sandwich terns usually nest in association with black-headed gulls, Larus ridibundus, and the benefits of this in terms of reduced predation risk may be an important reason for coloniality. © 1990 The Association for the Study of Animal Behaviour.