The effect of drought on body size, growth and abundance of wild brush-tailed phascogales (Phascogale tapoatafa) in south-western Australia

Abstract

Body size and growth data were gathered on 387 wild brush-tailed phascogales captured between 1992–1997 in south-western Australia. This marsupial has not previously been studied in Western Australia. Compared with Victorian phascogales, those in the south-west (single region) are typically 20–30% smaller in mass, smaller in skeletal measurements, and sexual size dimorphism is less. Habitat quality was correlated with body size and the largest phascogales were found in swamp/gully systems. These findings suggest food is a normally limiting resource for this species in the south-west environment. Additionally, a significant decrease in growth and size occurred during a drought year (1994), and growth of young seemed restricted during dependency. Maternal mortality appeared high during late lactation as orphaned, unweaned young were encountered in nest boxes. In 1995 adult males were 25% less in mass than usual; females 15% less. Population decline followed and by 1996 capture rates were 1/3 of that typically found for the time of year. Recovery was not apparent until two years after drought (early 1997). In this food-limited environment phascogale populations appear particularly vulnerable to annual fluctuations in rainfall.