RANGE EXTENSIONS AND THE BREEDING SEASONS OF SEABIRDS IN SOUTH-WESTERN AUSTRALIA

WA Museum Records and Supplements | Updated 1 decade ago

Abstract: Southward expansion of the ranges of some tropical seabirds, and the "double" nesting seasons of many seabirds on the mid-western and south-western coasts of Australia are re-examined in the light of recent studies of reproductive periodicity in the Crested Tern Sterna bergii and the Silver Gull Larus novaehollandiae and observations on other seabirds in south-western Australia. It is suggested that these range extensions and "double" nesting phenomena are influenced by a common environmental change, probably a seasonal influx of tropical water (the Leeuwin current).

There is evidence that the biogeographic origin of species determines their responses to environmental change. Thus species of tropical origin have extended their breeding ranges southwards. Autumn-nesting tropical populations of species secondarily adapted to the sub-tropics have also colonised the south-west, and in some locations nest in sympatry with spring-nesting populations already present. Species from high latitudes and of southern, cool-water origins have extended their breeding period into the autumn and increased their number of breeding attempts within a season.