POPULATION-DYNAMICS OF THE NEW-ZEALAND WHITEHEAD (PACHYCEPHALIDAE) - A COMMUNAL BREEDER

On Little Barrier Island, New Zealand, Whiteheads (Mohoua albicilla) reach high densities-a crude estimate of maximum density was 87 birds/ha. Males and females appeared to occupy home ranges of the same size. The sex ratio of mist-netted birds did not differ significantly from 1:1, but most helpers at the nest were males. The annual survival rate of independent mist-netted Whiteheads of unknown age was at least 0.82, yielding an estimated life expectancy of 5.1 years. Using Fry's method (1980) of generating survival curves we obtained an s10 value (mean age reached by 10% of birds initially at risk) of about five. The longest-lived birds in the study reached at least six years and seven months. At least 6 5% of fledglings survived their first year. Some dispersed from their natal area in their second or third years but others did not. In the best-studied case, a pair of Whiteheads bred communally by associating with their surviving young. These young helped raise later progeny. Young Whiteheads were seen associating with a parent for up to two years and seven months. We think that communal breeding in Whiteheads is a mechanism that allows young adults to mark time until an opportunity for breeding arises.