The Robbing Behaviour of Terns and Gulls

Abstract

The robbing behaviour of some larids at One Tree Island, Great Barrier Reef, was observed. Terns usually were moderately successful when robbing members of their own species but stole only a few fish brought into a colony. Between species, Roseate Terns rarely succeeded though they often tried to rob Black-naped Terns whereas Silver Gulls frequently succeeded and often tried to rob Lesser Crested and Crested Terns. The number of attempts by most species was greatest during high tide when the most pirates were round the colonies. The success of Silver Gulls varied in time and place. Some of the variables that affected the success were the number of Gulls attacking a tern, the length of the fish, the size of the pirate relative to its victim and the strategy used.