Climatic modelling of the Australian distribution of the grass owl (Tyto capensis): is there an inland population?

Abstract

The Australian distribution of the grass owl (Tyto capensis) is poorly understood. It has been proposed that there are two centres of distribution: a resident coastal population in the north-east, and a less stable inland population from which there is Australia-wide dispersal when good seasons are followed by deteriorating conditions. We analysed records of the grass owl and modelled its bioclimatic profile and distribution, which was typically subtropical, warm to hot humid with no dry season or a dry winter. This predicted a north-east sub-coastal to coastal, permanently occupied, core distribution for the owl. We found no evidence for a permanent or isolated inland population, nor for inland populations being the sole source of dispersers, as has been suggested previously. Most inland and northern records were made in the 1970s when grass owls colonised the arid inland, the Kimberley and the far north of the country in association with events leading to the flooding of Lake Eyre. The data suggest that grass owls disperse from their core range after exceptionally good breeding seasons to areas made temporarily favourable by exceptional rainfall or flooding, only to disperse again when conditions become drier. These dispersal events are not tied uniquely to outbreaks of the long-haired rat (Rattus villosissimus), but to a variety of terrestrial prey with dynamic life histories driven by rainfall.