Turnover in Breeding Bird Populations on Rottnest I. Western Australia

Abstract

The avifauna of Rottnest Island, W.A., has been surveyed four times between 1904 and 1983: by Lawson in 1904, Glauert (1928), Storr between 1953 and 1962, and ourselves between 1981 and 1983. There were three recorded extinctions and 10 immigrations in the 79-year period, but none of the extinctions and only three of the immigrations could be regarded as valid for calculating natural turnover rates. The remainder had been influenced by human activity; therefore the avifauna extinction rate for Rottnest Island was 0, the immigration rate was 0.04% per year for non-marine species of bird and the relative turnover rate for the 79 years was 0.12% per year. These results for Rottnest I. support the view of Abbott (1978, 1980) that for Australian islands, immigrations and extinctions are infrequent and turnover of breeding species is also infrequent. There have been 109 sightings of vagrants recorded for the island between 1905 and 1983; only one of these had individuals present in sufficient numbers during the breeding season to establish a breeding population. The data show that for one Australian island natural extinctions of both passerines and non-passerines are rare. Water does act as a barrier and although birds do cross water and often appear as vagrants, they very rarely do so in sufficient numbers or at the right time to establish breeding populations.