Some demographics of the extirpation from the wild of eastern barred bandicoots (Perameles gunni) in 1988-91, near Hamilton, Victoria, Australia

Abstract

The threatened, free-ranging mainland poplation, of the eastern barred bandicoot in the Hamilton area of Victoria declined to near extinction in late 1992. Demographic changes associated with the decline were monitored from 1988 to 1992. About 200 different animals were captured in 1988,49 in 1989, 16 in 1990, 3 in 1991 and 3 in 1992; capture rates (number of bandicoots captured per trap-night) displayed a similar pattern: 0.5 in 1988,O.l in 1989,0.05 in 1990,0.05 in 1991 and 0.02 in 1992. Observed declines lay within the 5% confidence intervals predicted by a demographic model for a population subjected to a removal rate of 14 animals per three months (the number removed for captive breeding by managers). Removal of bandicoots to stock a captive population hastened the demise of the wild population by about seven years; however, even in the absence of removals of animals, extinction was impending within 5-10 years. Sex ratios were male-biased in all years except 1988; the bias may have resulted from stochastic events. Average litter sizes did not differ between the 1988 population and subsequent populations, except for the 1991 population, in which a predominance of non-reproductive females contributed to a strong decline in average litter size. These demographic trends illustrate how the synergy between stochastic and deterministic forces can rapidly drive a small population to extinction.