SOCIAL BEHAVIOUR OF THE WHITE‐EYE ZOSTEROPS LATERALIS IN WINTER FLOCKS

Summary 1. In 1959 and 1960 observations on winter flocks of the White‐eye Zosterops lateralis were made at a feeding station and in an aviary at Dunedin, New Zealand. 2. Aggressive behaviour takes different patterns according to the intensity of aggression; ritualized pecking, threat display, incipient attack, combat and chasing are distinguished. Many components of the basic threat posture are similar to those of other passerine species, but “wing fluttering”, presentation of white underwing coverts and the brown colour on the flank, and “beak clattering” seem to be characteristic of the White‐eye. “Wing fluttering” is an incipient attack and often develops into an actual attack when stimulated by identical posturing by an opponent. 3. The pecking order found in the captive birds was a peck‐right hierarchy, but triangular relations were also observed when mated birds were involved. Prior residence was effective for a short period only and the despot in the prior occupants could be defeated by an aggressive intruder. 4. 710 birds were colour‐ringed at the feeding station, 306 returned and 204 were observed in aggressive encounters. The analysis of these encounters showed that in natural flocks dominant birds are engaged in aggressive encounters more frequently than subordinate birds, that dominants fight more often with birds of higher ranks, and that subordinates avoid encounters with aggressive birds. 5. A complex peck‐right hierarchy was found among members of different flocks visiting the feeding station. It is suggested that aggressive behaviour serves to establish and maintain the social hierarchy among individuals coming into contact over various objects. In crowded conditions severe fighting frequently takes place and the right of prior residence may be challenged constantly. 6. The importance of ecological implications of flocking and aggressive behaviour in the White‐eye population in New Zealand is discussed.