Although the theoretical effects of a severe reduction in effective population size (i.e. a bottleneck) are well known, relatively few empirical studies of bottlenecks have been based on extensive temporally spaced samples of a population both before and after a bottleneck. Here we describe the results of one such study, utilising the Jenolan Caves (JC) population of the brush-tailed rock-wallaby (Petrogale penicillata). When first sampled in 1985 (n = 20) the JC population comprised ~90 individuals. Subsequently the population crashed, and by 1992 only seven individuals remained. In 1996 the entire population (n = 10) was again sampled. Genetic diversity in the pre- and post-crash JC population was compared using 11 polymorphic microsatellite loci and PCR–SSCP analysis of the mitochondrial DNA control region. Only a single unique control region haplotype was detected in the pre- and post-crash JC population, although variant haplotypes were present in other P. penicillata populations. Of the 35 microsatellite alleles present in the pre-crash population, nine (26%) were lost during the bottleneck. The average number of rare alleles declined by 72%, allelic diversity was reduced by 30% and average heterozygosity declined by 10%. These observations are consistent with theoretical predictions. Additional analyses revealed that a P.�penicillata female at Wombeyan Caves was the only survivor of a 1990/91 reintroduction attempt using animals from JC. Of the microsatellite alleles detected in this female, 21% (4/19) were no longer present in the post-crash JC population. Furthermore, the genetic profiles of animals from the recently discovered Taralga population indicate that they are not derived from JC stock, but represent a threatened remnant of a hitherto undetected natural P. penicillata population.

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Predator scats were collected near colonies of the brush-tailed rock-wallaby, Petrogale penicillata, in gorges near Armidale, New South Wales. Scat collection coincided with the two periods when these macropodids are believed to be most vulnerable to predation: when juveniles vacate the pouch (September) and when they disperse from natal home ranges (April). The ratio of known dingo to fox scats did not differ significantly from 1 : 1 for each collection period. The most common dietary items identified in the scat analysis were as follows: rabbits (in 30% of scats); swamp wallabies (21%); cattle (16%); and brushtail possums (10%). Despite a visible abundance of P. penicillata in the study area, it occurred rarely (1%) in the 342 canid scats collected, and no P. penicillata was detected in fox scats. While the collection and analysis of predator scats does detect P. penicillata, it does not provide an efficient means of doing so and is unlikely to be effective at detecting small populations of this species.

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