This paper describes how environmental factors, survey method procedures and differences in forest structure resulting from logging relate to the detection of koomal (common brushtail possum, Trichosurus vulpecula hypoleucus) and ngwayir (western ringtail possum, Pseudocheirus occidentalis). A total of 169 vehiclebased spotlight surveys of possums within native jarrah (Eucalyptus marginata) forest was conducted on three transects over eight years (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). Up to 5.7 koomal and up to 3.3 ngwayir were detected per kilometre per transect side. Only one ngwayir was detected during the eight surveys conducted between 2001 and 2003. More koomal were seen in spring and autumn (i.e. September-November and March-May respectively) and more ngwayir were seen between October and April. Although surveys were not conducted on very rainy or excessively windy nights, fewer possums were nonetheless seen on nights following rainy days and on cold nights. Cloud cover also affected sightings of koomal. The time taken to complete the surveys increased in conjunction with the number of possums detected, on account of the time required to record data. The importance of standardising travelling speed also is emphasised. Possum spotlight counts differed between recently logged and unlogged areas. However, these findings were not supported by complementary koomal abundance estimates derived from trapping, suggesting that vegetation structure may affect detectability. Factors such as the lunar cycle, wind speed and survey start time after sunset did not significantly affect detection rates of either species. On the basis of these findings, specific survey conditions can be selected to improve spotlight detection efficiency.

Comparative trials of different survey methods were conducted in the southern jarrah (Eucalyptus marginata) forest to determine the most efficient means of detecting koomal (common brushtail possum, Trichosurus vulpecula hypoleucus) and ngwayir (western ringtail possum, Pseudocheirus occidentalis). In particular, we examined different trapping and spotlighting methods and compared these with scat surveys. Six different trapping methods (derived by combining three bait types and two trap positions) were compared at six sites. Significantly fewer koomal were caught on ‘universal’ bait (i.e. peanut butter, rolled oats and sardines) than on flour-based baits using rose oil or Eucalyptus oil as lures. Significantly more individuals of both possum species were caught in arboreal traps than in ground traps (P < 0.001 in both cases). Recapture rates of koomal were high, whereas ngwayir were rarely retrapped. There were no detection differences between six different spotlighting methods (derived by combining three spotlight intensities with two filter colours) for koomal. Significantly more ngwayir were detected using 50-W or 100-W lights than 20-W lights (P = 0.01). There were no significant differences in the detection rates for ngwayir using red or white light. There were, however, significant observer differences in the number of possums of both species detected (koomal, P = 0.025; ngwayir, P = 0.004). Spotlighting detected, on average, only 4.9% of the koomal ‘known to be alive’ by trapping. However, spotlighting with a 50-W or 100-W spotlight detected more ngwayir than did trapping. Koomal abundance measures derived from scat surveys were not related to trapping or spotlight abundance estimates. For ngwayir, however, scat counts were strongly related to spotlight counts and there were no significant observer differences for the former. We conclude that koomal are more effectively surveyed using arboreal trapping with rose or Eucalyptus lures. Ngwayir are best surveyed using scat surveys or 50-W spotlights.

Life-history attributes are described for the threatened ngwayir or western ringtail possum (Pseudocheirus occidentalis) in inland jarrah (Eucalyptus marginata) forest east of Manjimup, south-western Australia. Data on 81 individuals were collected over 18 months. There was no sexual dimorphism and body size was similar to that found in other P. occidentalis populations, but larger than the closely related P. peregrinus in eastern Australia. Breeding at Chariup was more strongly seasonal than that of coastal populations, with 77% of births in May–June and the remainder in October–November. All neonates were singletons except for one instance of non-viable twins. No females bred twice in the same year. The growth rate of the head length of pouch young (<5 months of age) was 0.245–0.362 mm day–1 and curvilinear toward an asymptote thereafter. Temporal variations in body condition, coat condition and ectoparasites were significant. Mortality was highly seasonal (84% of deaths were April–September) and predominantly caused by predation, mainly by fox (Vulpes vulpes) and cat (Felis catus). More effective and strategic control of introduced predators prior to and during autumn/winter, could therefore improve the viability of jarrah forest populations. Nutrition appears to influence many of the life-history traits of P. occidentalis. Nutrition also may partly explain the differences in size, life history and conservation status between P. occidentalis and P. peregrinus.

The common brushtail possum (Trichosurus vulpecula) is noted for its morphological, biological and ecological variability across its range. Despite having suffered substantial population declines since European settlement, relatively little has been published on the south-western Australian subspecies, the koomal (T. v. hypoleucus). This study reports morphological, reproductive and general life-history data from an 18-month study of a population in the southern jarrah (Eucalyptus marginata) forest at Chariup (part of Perup), near Manjimup, in south-western Australia. As one of the smallest subspecies, adult males of T. v. hypoleucus averaged 1616 g and females averaged 1470 g. Sexual dimorphism also occurred with head length and pes length, but not tail length. A single autumn breeding season occurred in both 2002 and 2003, in which all adult females bred and produced a single young between February and May. The onset of autumn births was associated with the end of the summer drought. Unlike many other Trichosurus populations, no spring breeding pulse or ‘double-breeding’ events were observed. At least 83% of pouch young survived to pouch emergence. The growth rate of offspring was initially linear, but became curvilinear and approached an asymptote after ~5 months. Most females bred for the first time when they were 1 year old. On the basis of testis size, males also matured at 1 year old. The body condition of adult males, but not adult females, changed significantly over time and followed an apparently seasonal pattern in which their condition was poorest in winter and best in summer. While many of the life-history traits of the Chariup population were similar to those of other south-western Australian populations of T. v. hypoleucus, the most striking variations included age at maturity, extent of spring breeding pulse and female fecundity. Further comparisons with conspecifics elsewhere in Australia and New Zealand also highlight the variability exhibited by T. vulpecula across its range. Some aspects of the biology of T. v. hypoleucus were particularly similar to those observed for T. v. arnhemensis in northern Australia.