COOPERATIVE BREEDING IN A POPULATION OF WHITEBROWED SPARROW WEAVERS <i>PLOCEPASSER MAHALI</i>

Abstract

Summary This paper reports on a three year study describing cooperative breeding and demography of a sampled population of approximately 108 colour‐marked White‐browed Sparrow Weavers in Zambia. Twenty‐seven communal groups with two to 11 individuals in a group made up this population and occupied a l km 2 area of mopane woodland. Each group had only a single reproductive pair and the pair‐bond appeared strong. Non‐reproductives were generally siblings or half‐siblings and they contributed a major share of nestling feeding, nest building, intruder chasing and guarding. Groups cooperatively built nests in certain preferred trees and they maintained their nests year round. Feeding range encircled the nesting site and was used almost exclusively by the communal group. Overall population density was relatively stable, and between‐year variation in group size was significantly greater than within‐year variation. Variation in annual reproductive success among groups was high and correlated positively with size. Mortality rates for nestlings, six‐month‐olds and juveniles were not correlated significantly with group size. Frequency of disappearance for reproductives of both sexes was correlated negatively with group size.