The population ecology of P. apodemoides was examined at two mature heathland localities in western Victoria. At the more mesic Little Desert site animals bred in spring and summer, but at the xeric Big Desert site they bred in winter. Such a discrepancy may arise from phenological differences between the two sites, rather than successional or climatic differences. Both populations were characterized by high levels of transience, and one instance of long-term dispersal was recorded. The breeding system may be promiscuous, and large; unstable groups of animals of both sexes may occupy individual burrows. The sex ratio at breeding was female-biased, which generates a capacity for rapid response to fluctuations in food resources. This is valuable in habitats frequently perturbed by fire and drought.