Reproductive demographics among brush-tailed phascogales (Phascogale tapoatafa) in south-western Australia

Abstract

Reproduction and population demographics were examined among wild brush-tailed phascogales in southern Western Australia. Data were gathered in a single region during 1992–97 from 387 individuals, 139 of whom were monitored by radio-telemetry. In contrast to Victorian phascogales, which all have eight teats, the Western Australian population contained females with six (30%), seven (21%), and eight (49%) teats (n = 72). Teat numbers varied between mothers and daughters/sisters, which appears unprecedented among dasyurids. The data strongly suggest that females try to raise as many young as they have teats. Population changes are as described for Victorian phascogales: complete male die-off occurs in July; some females survive to breed in a second year; and there is long-distance male dispersal and high philopatry by female offspring. Births occur from July to September, somewhat later and also less synchronised than among Victoria phascogales. Late breeding by females in one year suggests that sperm storage may be extensive in this species. Strong associations between the physical condition of females and rainfall suggest that these may influence between-year variation in birth times and sex-ratio bias in litters. Similarly, poor physical condition of young during drought may have underpinned atypical dispersal behaviour in males. Decreased teat numbers and smaller litter sizes indicate that phascogales from south-western Western Australia are reproductively adapted to relatively low food availability. However, this species experiences difficulty successfully breeding and rearing young under drought conditions.