Paul J. de Tores

Local population structure of a naturally occurring metapopulation of the quokka (Setonix brachyurus Macropodidae: Marsupialia)

We investigated the population structure of the quokka (Setonix brachyurus) on the mainland of Western Australia using mark– recapture techniques. Seven previously known local populations and one unconfirmed site supporting the preferred, patchy and discrete, swampy habitat of the quokka were trapped. The quokka is now considered as locally extinct at three sites. The five remaining sites had extremely low numbers, ranging from 1 to 36 individuals. Population density at these sites ranged from 0.07 to 4.3 individuals per hectare. There has been no response to the on-going, 6 year fox control programme occurring in the region despite the quokkas’ high fecundity and this is due to low recruitment levels. The remaining quokka populations in the northern jarrah forest appear to be the terminal remnants of a collapsing metapopulation. # 2002 Elsevier Science Ltd. All rights reserved.

Home range and movements of the quokka Setonix brachyurus (Macropodidae: Marsupialia), and its impact on the viability of the metapopulation on the Australian mainland

The home range and movements of the quokka Setonix brachyurus, a medium-sized macropodid marsupial, were investigated using radio telemetry. Fifty-eight quokkas from five remnant mainland populations in the northern jarrah (Eucalyptus marginata) forest of Western Australia were radio-collared and monitored for up to 2 years between 1998 and 2000. Mean (± SE) home-range sizes were 6.39 ± 0.77 ha and core ranges averaged 1.21 ± 0.12 ha. Male core home ranges were larger than those of females although not when corrected for body mass. Nocturnal ranges were larger than diurnal owing to nocturnal departures from the swamp. Ranges shifted to the edge of swamps in winter, as the swamps became inundated following rain, and toward the centre in autumn as the swamps dried. Quokka populations are thought to exist below carrying capacity at all sites and this probably caused the lack of dispersal observed in this study. We hypothesize that predation is suppressing population booms which would otherwise drive dispersal and thereby maintain metapopulation dynamics. Without dispersal to rescue unpopulated patches, we conclude that the original quokka metapopulation has collapsed and ameliatory measures are required.

HABITAT USE OF THE QUOKKA, SETONIX BRACHYURUS (MACROPODIDAE: MARSUPIALIA), IN THE NORTHERN JARRAH FOREST OF AUSTRALIA

Abstract Habitat use of quokka (Setonix brachyurus) in the northern jarrah forest of Western Australia was determined by monitoring movements of 58 quokkas over 2 years in 5 local populations. Quokkas were largely restricted to Agonis swamps that occur patchily throughout the jarrah forest. Within swamps, they are habitat specialists, preferring early seral stages that have been burned within the previous 10 years. This preference derives from a combination of dietary requirements and refuge from predation. As swamps mature they become suboptimal, forcing quokkas to colonize new patches. Since the collapse of the metapopulation following the introduction of the European red fox (Vulpes vulpes) in the 1930s, quokkas have been forced to remain at a site because predation inhibits dispersal.

Predicting the occurrence of the quokka, Setonix brachyurus (Macropodidae : Marsupialia), in Western Australia’s northern jarrah forest

The quokka, Setonix brachyurus, is a medium-sized, macropodid marsupial that is endemic to south-western Australia. It has declined markedly in its distribution and abundance since the early 1930s and is listed as vulnerable under IUCN criteria. The presence or absence of quokka populations at 66 sites in the northern jarrah forest of Australia was investigated using generalised linear models (GLM). We hypothesised that fox control and the presence of a mosaic of post-fire seral stages within Agonis linearifolia swamp vegetation were important in predicting the presence of quokkas. The number of poison meat baits delivered per hectare, the average number of years since the swamps burnt and the number of post-fire age classes within the swamps (mosaic value) were used as explanatory variables. Two models had substantial support (ΔAICc 19 years since fire) are essential for its conservation.

Mortality and survivorship of the quokka (Setonix brachyurus) (Macropodidae : Marsupialia) in the northern jarrah forest of Western Australia

The potential for the quokka (Setonix brachyurus (Quoy & Gaimard, 1830)), a threatened macropodid marsupial, to increase in abundance following the initiation of predator control was investigated by determining the cause of deaths of radio-collared individuals. Predation was identified as a major cause of death followed by road kills. The non-parametric Kaplan-Meier method modified for staggered entry of individuals was used to estimate survivorship. Although males and females were affected differently by each cause of mortality, their overall survivorship did not differ significantly. Individuals alive at the beginning of the 25-month study had a 61% chance of surviving to the end. This represented an 81% chance of surviving for 1 year. There was no significant difference in survivorship between adults and juveniles. Current rates of adult and juvenile survivorship should allow population recovery, although none has been evident. Pouch young mortality is hypothesised to have inhibited the anticipated quokka population increase since the initiation of predator control. The observed expulsion of pouch young by females when threatened may be a primary predator avoidance strategy.

Using faecal pellet counts along transects to estimate quokka (Setonix brachyurus) population density

A study was conducted to determine the validity of using transect counts of faecal pellet groups to estimate population densities of a threatened, macropodid marsupial – the quokka (Setonix brachyurus (Quoy & Gaimard, 1830)). Mark–recapture estimates of population density were regressed against counts of faecal pellet groups at six sites with and three sites without fox control within the northern jarrah forest of Western Australia. Significant linear relationships were found between population density and pellet counts for all sites (r2 = 0.56, P < 0.02) and when all unbaited sites were excluded (r2 = 0.98, P < 0.01). We suggest that this method could be used for broad-scale monitoring of this threatened species.

Estimating the population size of a threatened arboreal marsupial: use of distance sampling to dispense with ad hoc survey techniques

Context. Long-term land-use decisions potentially affecting the conservation status of rare fauna are often based on a dearth of relevant biological information and population estimates are regularly derived from ad hoc methodologies. This can significantly affect the outcomes from development assessment and approval processes. Aim. Our aims were to apply distance-sampling techniques to derive robust, quantitative estimates of the population size of a threatened arboreal marsupial, the western ringtail possum (Pseudocheirus occidentalis Thomas, 1888), demonstrate the advantages of this approach and, in doing so, provide conservation managers, decision makers and consultants with a reliable framework for surveying the species. Methods. We used line-transect sampling to derive estimates of density and abundance for P. occidentalis at two sites in south-western Western Australia where estimates were previously derived through ad hoc techniques. Key results. Our findings support the assertion that previous surveys of P. occidentalis populations have underestimated the population size to a varying extent at both of our survey sites. Land-use and development-application decisions have previously been based on similar surveys. Conclusions. Distance sampling, if applied routinely when surveying P. occidentalis, will reduce the uncertainty associated with derived estimates of abundance. Implications. Appropriate use of distance-sampling methods will enable managers and decision makers to assess more quantitatively the potential effect from, and place appropriate approval conditions on, proposals that modify or destroy P. occidentalis habitat. The use of the program Distance will enable such decisions to be based on robust, repeatable estimates of population size, with quantified confidence limits and variance estimates.

Hematologic and serum biochemical reference ranges and an assessment of exposure to infectious diseases prior to translocation of the threatened western ringtail possum (Pseudocheirus occidentalis)

Abstract Health screening of animals before translocation is important to minimize the risk of pathogen transmission between sites and species. Reintroduction has been incorporated into management of the endangered western ringtail possum (Pseudocheirus occidentalis) to mitigate for habitat loss within the species core range in southwestern Australia. Between November 2005 and March 2008 we screened 47 wild and 24 captive P. occidentalis and 68 sympatric common brushtail possums (Trichosurus vulpecula hypoleucus) for infectious diseases that might compromise possum survival or fecundity at translocation sites. We found no evidence that infectious disease limits translocation success, and neither possum species showed evidence of infection with Salmonella spp., Toxoplasma gondii, Leptospira spp., or Chlamydophila spp. Antigen of Cryptococcus gattii was detected in one T. v. hypoleucus but was not of pathologic significance. Hematologic and serum biochemical reference ranges were determined for 81 wild and 24 captive P. occidentalis. Site differences were identified for red blood cell count, hemoglobin, albumin, urea, and globulin, suggesting that habitat quality or nutrient intake may vary among sites. Differences between wild and captive values were found for several parameters. These data are useful for health evaluations of injured P. occidentalis and the future monitoring of wild populations.

Detecting, but not affecting, nest-box occupancy

Context. Nest boxes are a useful tool in the reintroduction, conservation and monitoring of many hollow-using species. Aims. All forms of nest-box monitoring involve some form of invasion, often upsetting their continued use by occupants. We conducted a pilot study to investigate and validate the innovative use of temperature dataloggers (iButtons®) to remotely monitor nest-box use, leaving the nest-box occupants untouched. Methods. In captivity, iButton recordings revealed the duration and time of day when each of the three nest-box designs was occupied by Pseudocheirus occidentalis (western ringtail possums); the accuracy of occupancy data was validated by unobtrusive infrared video recording. In the field, where translocated P. occidentalis and naturally occurring Trichosurus vulpecula (common brushtail possum) populations are present, hair sampling at the nest-box entrances (in addition to iButton recording) was used to identify the mammal species present. Key results. Nest-box use by captive P. occidentalis validated iButtons as a useful remote-monitoring tool, with 10u2009h) periods of continuous occupancy (T. vulpecula only). In addition to the convenience (to researcher and animal) of continuous (24-h) monitoring with minimal disturbance, a major advantage from using iButtons is that occupancy can be matched with environmental temperature or rainfall records, as well as other events (e.g. storms or frost). Conclusions. iButtons are a useful remote-monitoring tool of nest boxes, and it is possible that their use in this manner may be extended to tree-hollow occupation. Most importantly, this approach can inform us as to the conditions under which the nest boxes are used by fauna, as well as preferences for different nest-box designs. Implications. It is important to note that the criteria used for determining the presence or absence in the nest box (i.e. temperature difference, Tin– Tout, of 2°C) in the present study will not be relevant for all nest-box designs and before using these methods, the thermal properties of the nest box or tree hollow will require investigation.