Breeding and dominance among the Heron Island Silvereyes Zosterops lateralis chlorocephala

Abstract

The Heron Island population of Silvereyes with a known age distribution was followed through the breeding season. Its breeding cycle is described and the data on the 1969/70 season are used to find out how the dominance status of individual birds in winter affects their breeding performance. Most "floaters" were subordinate first-year birds and among the breeders older birds tended to produce more fledglings than younger birds. Clutch size was nearly constant and variation in brood size was not dependent on age or dominance of parents. The young of the intermediate class of parents had the greatest rate of survival till the winter. The dominant birds tended to nest in food-rich areas in crowded conditions, but the survival rate of their young was not related to the area of their origin. The dominant parents made the greatest contribution and the subordinate parents the least to the number of young surviving till the following breeding season. Thus selection with respect to dominance favoured the dominant birds during the high- density phase of 1969/70. Being dominant in the breeding context means that it enables the individual to establish a nesting territory which offers easy access to concentrated food. Territoriality appears to limit the number of nesting territories in the high-density area. Territorial defence is thought to play an important role in the protection of the nest; this is more effective if parents forage closer to the nesting area.