Influence of interactive effects on long-term population trajectories in multispecies reintroductions

Reintroduced populations are typically considered to progress through establishment, growth, and regulatory phases. However, most reintroduction programs do not monitor intensively enough to test this conceptual model. We studied population indices derived from track activity of 4 threatened species (greater bilby [Macrotis lagotis], burrowing bettong [Bettongia lesueur], greater stick-nest rat [Leporillus conditor], and Shark Bay bandicoot [Perameles bougainville]) over 23 years after multiple reintroductions of each species in arid Australia. We compared population trajectories among species and investigated the effect of time and environmental variables. All species bred immediately after release, and the growth phase lasted 3-16 years, varying markedly among but not within species. The end of the growth phase was characterized by an obvious peak in population density followed by either a catastrophic decline and sustained low density (bettongs), a slow decline to extirpation after 20 years (stick-nest rat), or a slight decline followed by irregular fluctuations (bilby and bandicoot). Minor fluctuations were related to environmental variables, including 12-month cumulative rainfall and lagged summer maximum temperatures. Three of the 4 species did not reach a regulation phase, even after 23 years, possibly due to interspecific competition and trophic cascades triggered by predator removal and multispecies reintroductions. Bilbies and bandicoots exhibited a second growth phase 18 years after reintroduction, likely caused by high rainfall and increased resources following the population crash of overabundant bettongs. Our results suggest that assemblages within multispecies reintroductions demonstrate high variability in population trajectories due to interactive effects. Intensive monitoring to assess population viability may require decades, particularly where multiple species are reintroduced, release sites are confined, and the climate is unpredictable. Intensive monitoring also allows for adaptive management to prevent precipitous population declines. Practitioners should not assume reintroduced species pass through predictable postrelease population phases or that viability is assured after a certain period.

A trial of transmitter attachment methods for Shark Bay bandicoots (Perameles bougainville)

In mammal reintroductions, effective post-release monitoring often relies on the use of radio-transmitters. Collars are a popular attachment technique but are not necessarily appropriate for all taxa. However, other attachment methods may result in substantially reduced monitoring durations. We assessed several transmitter types for the Shark Bay bandicoot (Perameles bougainville), aiming to optimise animal welfare and attachment duration. Collars (fitted under general anaesthetic) were considered the optimal method and 12 bandicoots were collared and monitored as part of a reintroduction program. We found that our collars permitted monitoring for up to seven weeks, while causing minimal harm to the animals.

Genetic analysis of three remnant populations of the rufous hare-wallaby (Lagorchestes hirsutus) in arid Australia

The rufous hare-wallaby (Lagorchestes hirsutus) is now extinct in the wild on mainland Australia, but survives in captivity. However, endemic populations persist on Bernier and Dorre Islands, Western Australia. This study aimed to compare the genetic diversity and differentiation amongst three remaining rufous hare-wallaby populations using mitochondrial DNA (mtDNA) (cytochrome b, control region) sequence data and nuclear (microsatellite) markers. Levels of microsatellite diversity were low in both island populations but high in the captive mainland population. Levels of mtDNA diversity were low in all three populations. The mainland and island populations of L. hirsutus were found to be significantly differentiated for both microsatellite and mtDNA data, but the two island populations were significantly differentiated only for the microsatellite data. This pattern of differentiation is not consistent with the recognition of two separate island subspecies, but we recommend that the mainland and island populations be regarded as separate subspecies. The low diversity of the island populations and differentiation between island and mainland populations presents both challenges and opportunities for future management.

Evidence of significantly higher island feral cat abundance compared with the adjacent mainland

Context Feral cats (Felis catus) impact the health and welfare of wildlife, livestock and humans worldwide. They are particularly damaging where they have been introduced into island countries such as Australia and New Zealand, where native prey species evolved without feline predators. Kangaroo Island, in South Australia, is Australia’s third largest island and supports several threatened and endemic species. Cat densities on Kangaroo Island are thought to be greater than those on the adjacent South Australian mainland, based on one cat density estimate on the island that is higher than most estimates from the mainland. The prevalence of cat-borne disease in cats and sheep is also higher on Kangaroo Island than the mainland, suggesting higher cat densities. A recent continental-scale spatial model of cat density predicted that cat density on Kangaroo Island should be about double that of the adjacent mainland. However, although cats are believed to have severe impacts on some native species on the island, other species that are generally considered vulnerable to cat predation have relatively secure populations on the island compared with the mainland. Aims The present study aimed to compare feral cat abundance between Kangaroo Island and the adjacent South Australian mainland using simultaneous standardised methods. Based on previous findings, we predicted that the relative abundance of feral cats on Kangaroo Island would be approximately double that on the South Australian mainland. Methods Standardised camera trap surveys were used to simultaneously estimate the relative abundance of feral cats on Kangaroo Island and the adjacent South Australian mainland. Survey data were analysed using the Royle–Nichols abundance-induced heterogeneity model to estimate feral cat relative abundance at each site. Key results Cat abundance on the island was estimated to be over 10 times greater than that on the adjacent mainland. Conclusions Consistent with predictions, cat abundance on the island was greater than on the adjacent mainland. However, the magnitude of this difference was much greater than expected. Implications The findings show that the actual densities of cats at local sites can vary substantially from predictions generated by continental-scale models. The study also demonstrates the value of estimating abundance or density simultaneously across sites using standardised methods.

The biology and palaeontology of the Peramelemorphia: a review of current knowledge and future research directions

Bandicoots and bilbies (Marsupialia : Peramelemorphia) represent the dominant omnivorous clade of Australasian marsupials and, as ground-dwelling, small- to medium-sized mammals, have not fared well in the 200 years since European settlement. Unlike large or charismatic marsupial species, the cryptic nature of bandicoots and bilbies tends to keep them out of the public eye, at a time when public interest plays a significant role in conservation efforts. The inconspicuous ‘rat-like’ appearance of many bandicoots and a generalist ecological strategy belie a complex biology of adaptive traits and evolutionary diversity. For a few species these biological traits have enabled them to make use of urban environments. In the main, however, peramelemorphians are facing ongoing pressure from introduced predators and human impacts. Basic biological information for many species, particularly those from New Guinea, is still lacking. In this review, we examine advances in the knowledge of the biology of this group over the past 25 years including anatomical, physiological and ecological studies. We also provide a comprehensive review of the fossil records of bandicoots in order to provide an up-to-date platform for future studies. From this work, it is clear that there is still much to be done regarding the taxonomy and biology of these animals before a more detailed understanding of the evolutionary history of this group can be elucidated.

Predation by feral cats key to the failure of a long-term reintroduction of the western barred bandicoot (Perameles bougainville)

Context Reintroduction of endangered species potentially places them back in contact with putative factors of historical decline, inadvertently providing the opportunity to evaluate their impact. Aims To monitor the long-term progress of a population of western barred bandicoot reintroduced to mainland Australia and to assess factors involved in its eventual local extinction. Methods Bandicoots were reintroduced from offshore Dorre Island to the nearby mainland peninsula of Heirisson Prong in 1995. The narrow neck of the peninsula was fenced to exclude foxes and feral cats from a 1200 ha area, but the area was subject to periodic incursions. There was parallel management of a confined but unsupported population in an in situ 17-ha predator refuge. Bandicoots were assessed for abundance, body condition and reproduction two to four times annually between 1995 and 2010. In addition, perceived threatening processes (drought, disease and the abundance of cats, foxes and rabbits) were monitored. Key results Bandicoots became well established at the site, spreading to all available habitat. Numbers fluctuated strongly, peaking at ~250 in 1999 and then declining to apparent local extinction (with subsequent re-establishment from the refuge), and at ~470 animals in 2006, followed again by extinction. Conclusions Predation by feral cats was implicated as the primary cause of both free-range extinctions and the eventual elimination of all bandicoots from the predator refuge. Other contributing factors in one or more of the declines were a reduction in reproduction and recruitment in bandicoots during a one-in-100-year drought, the impact of overabundant European rabbits on vegetation used by bandicoots for nesting shelter and brief fox incursions at key times. Implications Existing methods of control of feral cats are rendered ineffective in the presence of abundant and diverse native fauna and abundant exotic species (particularly European rabbits). In addition, episodic drought in arid Australia intensifies the impact of predation by restricting reproduction of prey species. These factors hamper the attempts of conservation managers to re-establish vulnerable species at sites other than those with the infrastructure and/or management intensity to largely exclude exotic predators (and preferably European rabbits) over the long-term.

Aspects of the ecology of the kalubu bandicoot (Echymipera kalubu) and observations on Raffray’s bandicoot (Peroryctes raffrayanus), Eastern Highlands Province, Papua New Guinea

Bandicoots in the family Peroryctidae in New Guinea are widespread and relatively abundant, but little is known of their ecology. We present the first detailed study on the ecology of the kalubu bandicoot (Echymipera kalubu) and observations on Raffray’s bandicoot (Peroryctes raffrayanus), from mid-montane forest in Papua New Guinea. Both species were primarily nocturnal and utilised a range of habitats including those modified by human activity, although Raffray’s bandicoot was more frequently encountered in less disturbed areas. Male kalubu bandicoots were larger than females, with larger animals having larger short-term home ranges and evidence for intrasexual territoriality. Mean short-term home-range size was 2.8 ha (MCP, n = 10), with an estimated population density of ~85 animals km–2 in the study area. Female kalubu bandicoots attained sexual maturity at ~400 g and 67% of mature females were reproductively active with an average of 1.5 young per litter. Both species were hunted, but their density, rate of reproduction and use of modified habitats suggest that they were able to withstand current hunting levels.

Faecal glucocorticoid metabolite concentrations in the free-ranging bandicoots (Perameles nasuta and Isoodon obesulus) of northern Sydney

Knowledge of how animals cope with their environment is fundamental to the management of free-ranging populations. Urban animals face increased competition for resources, habitat fragmentation and predation. These pressures may impact an individual’s welfare by releasing glucocorticoid hormones in the blood through a response from the hypothalamic–pituitary–adrenal axis, resulting in altered energy storage and utilisation. This study aimed to determine the applicability of measuring faecal glucocorticoid metabolites in free-ranging bandicoots by using a simple enzyme immunoassay. We used long-nosed and southern brown bandicoots in northern Sydney to investigate whether environmental and demographic variables can influence faecal glucocorticoid metabolites. Long-nosed bandicoots showed similar faecal glucocorticoid metabolite concentrations between suburban backyards and National Park populations. Higher faecal glucocorticoid metabolites were recorded in female southern brown bandicoots than in males, whilst female and male long-nosed bandicoots had similar glucocorticoid metabolite levels. Ectoparasite load, body condition and season did not influence faecal glucocorticoid metabolites. This non-invasive method has a broad application and can be used to provide biological information to guide management of populations within a conservation context.

Prevalence, emergence, and factors associated with a viral papillomatosis and carcinomatosis syndrome in wild, reintroduced, and captive western barred bandicoots (Perameles bougainville)

Once widespread across western and southern Australia, wild populations of the western barred bandicoot (WBB) are now only found on Bernier and Dorre Islands, Western Australia. Conservation efforts to prevent the extinction of the WBB are presently hampered by a papillomatosis and carcinomatosis syndrome identified in captive and wild bandicoots, associated with infection with the bandicoot papillomatosis carcinomatosis virus type 1 (BPCV1). This study examined the prevalence and distribution of BPCV1 and the associated syndrome in two island and four mainland (reintroduced and captive) WBB populations in Western Australia, and factors that may be associated with susceptibility to this syndrome. BPCV1 and the syndrome were found in the wild WBB population at Red Cliff on Bernier Island, and in mainland populations established from all or a proportion of founder WBBs from Red Cliff. BPCV1 and the syndrome were not found in the wild population on Dorre Island or in the mainland population founded by animals exclusively from Dorre Island. Findings suggested that BPCV1 and the syndrome were disseminated into mainland WBB populations through the introduction of affected WBBs from Red Cliff. No difference in susceptibility to the syndrome was found between Dorre Island, Bernier Island, and island-cross individuals. Severity of lesions and the number of affected animals observed in captivity was greater than that observed in wild populations. This study provided epidemiological evidence to support the pathological and molecular association between BPCV1 infection and the papillomatosis and carcinomatosis syndrome and revealed increasing age as an additional risk factor for this disease.