The effects of drought on prey selection of the barn owl (Tyto alba) in the Strzelecki Regional Reserve, north-eastern South Australia

Changes in the diet of the barn owl (Tyto alba) were determined by analysing 619 egested pellets collected in eight samples over 12 months from a roost in the Strzelecki Regional Reserve, north-eastern South Australia. These data were used to examine the occurrence and change in frequency of small vertebrates in the region. In January 2003, at the end of a prolonged dry period, reptiles (predominantly geckos) dominated the diet of the barn owl, forming over 74% of Prey Units (PU%). This is the first Australian study to report reptiles as the primary prey of the barn owl. After substantial rain in February 2003, mammalian prey became much more common, and eventually accounted for almost 80 PU%. At least nine species of small mammal, at least four reptiles, nine birds and a frog were identified from the pellets. Mammalian prey included Leggadina forresti, Mus musculus, Notomys fuscus (endangered), Pseudomys desertor (not previously recorded in the reserve), P. hermannsburgensis, Planigale gilesi, Sminthopsis crassicaudata, S. macroura and Tadarida australis. This research showed that barn owls are capable of switching to alternative prey when mammals become rare, but that they return to preferred prey as soon as it becomes available.