Bridled Nailtail Research Articles

The impact of headstarting on the survival and naiveté of an endangered terrestrial mammal after return to the wild

AbstractComplete separation of endangered prey from introduced predators improves prey survival at the cost of reduced predator recognition and antipredator behaviours, termed ‘prey naiveté’. Headstarting is a conservation strategy that has been used to improve the survival of juveniles for numerous species, whereby prey is separated from predators only in their vulnerable early life stage before release to the wild. However, by isolating prey from predators headstarting could compromise prey individuals’ antipredator behaviour. Here, we evaluate the effects that headstarting has on the survival, dispersal, body condition and flight initiation distance (FID) of a terrestrial mammal, the bridled nailtail wallaby Onychogalea fraenata. Young bridled nailtail wallabies were isolated from predators in a 9.2 ha predator‐free fenced exclosure and were released into the wild once their body mass exceeded 3 kg. There was no difference in dispersal, body condition or survival of headstarted wallabies compared to wild‐raised wallabies. FID of headstarted wallabies assessed using night‐vision goggles was lower than wild‐raised wallabies in the week following release, but converged with that of wild‐raised wallabies within 4 weeks post‐release. Our results show that headstarting can be an effective conservation strategy for terrestrial mammals whose early life stages are vulnerable to introduced predators.

Evaluating institutional fit for the conservation of threatened species.

Recovery and conservation of threatened species require adequate institutional responses. We tested an approach to systematically identify and measure how an institutional framework acknowledges threats and required responses for the recovery of endangered species. We measured institutional functional fit with a drivers-pressure-state-impacts-response (DPSIR) model integrated with a quantitative text mining method and qualitative analysis of statutory instruments to examine regulatory responses that support the recovery of 2 endangered species native to Australia, the bridled nailtail wallaby (Onychogalea fraenata) and the Eastern Bristlebird (Dasyornis brachypterus). The key components of the DPSIR model were present in the institutional framework at statutory and operational levels, but some institutional gaps remained in the protection and recovery of the Eastern Bristlebird, including feral predator control, weed control, and grazing management in some locations. However, regulatory frameworks varied in their geographic scope and the application and implementation of many instruments remained optional. Quantitative text mining can be used to quickly navigate a large volume of regulatory documents, but challenges remain in selection of terms, queries of co-occurrence, and interpretation of word frequency counts. To inform policy, we recommend that quantitative assessments of institutional fit be complemented with qualitative analysis and interpreted in light of the sociopolitical and institutional context.

Headstarting as a cost-effective conservation strategy for an endangered mammal

Introduced predators threaten prey species worldwide, but strategies to protect vulnerable wildlife from introduced predators can be expensive, time-consuming, and logistically difficult1,2. Novel conservation strategies that reduce predation affordably and efficiently must be explored. 'Headstarting' is one such strategy, whereby prey are isolated from predators only during the critical early life stage before being returned to the wild, thus improving juvenile survivorship and recruitment to contribute to an increase in population growth3. Headstarting is a particularly useful conservation strategy for species facing higher levels of a threatening process during only the early part of their life history when mortality rates are higher, and has demonstrably improved conservation outcomes for birds and marine species3,4. Here we report findings from the first known headstarting program for a terrestrial mammal, the endangered bridled nailtail wallaby (Onychogalea fraenata) at Avocet Nature Refuge (henceforth 'Avocet') in Queensland, Australia.

Toxoplasma gondii seroprevalence in endangered bridled nailtail wallabies and co-occurring species

The parasite Toxoplasma gondii can infect any warm-blooded species; however, seroprevalence in most species remains largely unknown. In this study we examined the presence of T. gondii antibodies in captured individuals in the two remaining wild populations and one captive population of endangered bridled nailtail wallabies (Onychogalea fraenata). Samples from cats (Felis catus), rabbits (Oryctolagus cuniculus) and dogs (Canis lupus) were also taken opportunistically during invasive species control at the two wild populations. Seventy-one wallabies, sixteen cats, four rabbits, and two dogs’ blood samples were tested for T. gondii using a modified agglutination test. Half of the tested feral cats (n = 8) were seropositive and all intermediate hosts were seronegative for T. gondii antibodies. This unexpected result suggests a loss of infected individuals before capture and testing, or parasite infectivity being suppressed by Queensland’s hot, dry climate.

Patterns of habitat use by three threatened mammals 10 years after reintroduction into a fenced reserve free of introduced predators

Introduced predators are a major driver of global biodiversity loss. Over the last 200 years, the distribution and abundance of critical-weight-range mammals in Australia has declined, with many species now locally extinct or confined to small isolated refuges. From 2004 onwards as part of a major conservation initiative, the Australian Wildlife Conservancy reintroduced three threatened mammal species, the Greater Bilby (Macrotis lagotis), Bridled Nailtail Wallaby (Onychogalea fraenata) and Numbat (Myrmecobius fasciatus), into an 8000-hectare area protected by conservation fencing at Scotia Sanctuary in semi-arid New South Wales. Our study examined habitat selection for these species following multiple generations in a fenced area free of introduced predators.We used nocturnal spotlighting and diurnal search transect data collected over a two-year period to identify habitat preferences for these species, a decade after release. We used a Distance Sampling approach to examine differences in detectability between vegetation types, and Chi-Squared tests to identify differences in habitat use relative to availability. We used a Utilization Distribution (UD) analysis to identify how the spatial distribution of habitat affected its usage at Scotia Sanctuary. Habitat use of each species was compared with the results of a study conducted shortly after initial releases.We found that patterns of habitat use for these species differed to those identified following their initial release. We found a strong preference for shrub vegetation communities for all species relative to availability, as well as some variation in habitat preferences between two fenced areas (Stage 1 and Stage 2). The UD analysis revealed patterns of habitat use for one species (Bilby) that were not apparent from Chi-squared analysis, highlighting the importance of considering the spatial heterogeneity and proximity of different vegetation types when identifying species preferences.Our results demonstrate that in the absence of introduced predators these threatened species are able to use all of the vegetation types available, and by altering their habitat use over time, to persist following reintroduction into contemporary contexts within their historic ranges.

Microchips for macropods: First use of a microchip-automated door by a bridled nailtail wallaby (Onychogalea fraenata).

Commercially available microchip-automated devices for companion animals also have potential application with captive wildlife. To explore this potential, a captive bridled nailtail wallaby was trained to use a SureFlap Microchip Pet Door. Throughout the 62 day study the wallaby's interactions with the door increased in frequency and intensity, culminating in the repeated use of the microchip-automated door. This was the first record of any captive macropod being trained to use a microchip-automated device and demonstrates proof-of-concept that captive macropods can successfully utilize commercially available microchip-automated devices. Further research is recommended to develop methodology and evaluation techniques for training captive macropods while also exploring intra- and inter-species variations in responses.

Costs are key when reintroducing threatened species to multiple release sites

AbstractThreatened species with reduced and fragmented habitats can be reintroduced into their historical ranges to establish new populations. Multiple sites might be an option for reintroductions; therefore, managers must determine when to open sites (e.g. establish infrastructure and improve conditions), release individuals into those sites, and eventually cease releases. Careful planning of this schedule, incorporating the cost of actions, is imperative at the outset of a program. To address this challenge, we consider a reintroduction plan under different cost scenarios for three potential reintroduction sites. In particular, we investigate the implications of having either no ongoing site‐management cost, a financial ongoing site‐management cost, or a demographic cost of continuous releases. We couple population and management models to find a schedule that maximizes total abundance over time of bridled nail‐tail wallabyOnychogalea fraenata(released in fixed numbers each breeding season from a stable source population) using stochastic dynamic programming. We find that the type of ongoing cost influences the structure of the optimal schedule. If active release sites cost nothing to maintain, there is no incentive to cease releases. In that case, the optimal schedule is to open sites sequentially, then release individuals to the smallest active population for the entire length of the program. A financial cost for managing active sites alters this result; once all sites are open and have populations of a critical threshold size, sites should be closed sequentially. A higher mortality rate (demographic cost) at active compared to inactive sites completely changes the structure of the optimal strategy. Instead of opening all sites in the first few management stages, only one site should be active any time to reduce the demographic impact of releases. Our general results provide a guide for planning future reintroduction programs and illustrate the importance of categorizing and understanding ongoing costs for reintroduction planning.

The common gamma chain cytokine interleukin-21 is expressed by activated lymphocytes from two macropod marsupials, Macropus eugenii and Onychogalea fraenata.

In mammals, interleukin-21 is a member of the common gamma chain cytokine family that also includes IL-2, IL-4, IL-7, IL-9 and IL-15. IL-21 has pleiotropic effects on both myeloid and lymphoid immune cells and as a consequence, the biological actions of IL-21 are broad: regulating both innate and adaptive immune responses and playing a pivotal role in antiviral, inflammatory and antitumour cellular responses. While IL-21 genes have been characterized in mammals, birds, fish and amphibians, there are no reports for any marsupial species to date. We characterized the expressed IL-21 gene from immune tissues of two macropod species, the tammar wallaby (Macropus eugenii), a model macropod, and the closely related endangered bridled nailtail wallaby (Onychogalea fraenata). The open reading frame of macropod IL-21 is 462 nucleotides in length and encodes a 153-mer putative protein that has 46% identity with human IL-21. Despite the somewhat low amino acid conservation with other mammals, structural elements and residues essential for IL-21 conformation and receptor association were conserved in the macropod IL-21 predicted peptides. The detection of IL-21 gene expression in T-cell-enriched tissues, combined with analysis of the promotor region of the tammar wallaby gene, suggests that macropod IL-21 is expressed in stimulated T cells but is not readily detected in other cells and tissues. The similarity of gene expression profile and functionally important amino acid residues to eutherian IL-21 makes it unlikely that the differences in B- and T-cell responses that are reported for some marsupial species are due to a lack of important functional residues or IL-21 gene expression in this group of mammals.

Net effects of soil disturbance and herbivory on vegetation by a re-established digging mammal assemblage in arid zone Australia

Large-scale re-introductions of locally extinct digging mammal assemblages have been implemented at a number of arid zone sites, with the aim of conserving mammal species and restoring ecosystem function. Previous studies have focused on the ways in which foraging pits benefit plants, but the effects of herbivory by digging mammal assemblages are poorly understood.We used a randomised block design with control, procedural control and exclusion plots (n = 10) to experimentally test the net effect of a re-established mammal assemblage of bridled nailtail wallabies, Onychogalea fraenata, greater bilbies, Macrotis lagotis, brush tailed-bettongs, Bettongia penicillata, and burrowing bettongs, Bettongia lesueur, on plants in the Australian arid zone.We found that the re-established mammal assemblage limited natural seedling abundance and consumed transplanted seedlings. Plant composition between treatments did not differ, but perennial forbs and subshrubs, which are known food items of the re-introduced mammals, were most abundant in mammal exclusions. Furthermore, a landscape-scale survey showed that composition in the re-introduction area differed significantly from an adjacent control.When conceptualising the role of mammalian ecosystem engineers in arid environments, negative effects on plants from herbivory and soil disturbance must be considered alongside the better studied processes of nutrient cycling and seedling establishment.

High density, maternal condition, and stress are associated with male-biased sex allocation in a marsupial

Many mammals have been reported to significantly bias their offspring sex ratios, but these deviations from equality have been difficult to understand and are often inconsistent even within the same species. Evolutionary theory predicts a number of scenarios where females should bias their investment to one sex over the other; when fitness returns are sex specific, selection favors the facultative adjustment of offspring sex ratios to the sex with the highest inclusive fitness return. Interpreting sex allocation in mammals within the framework of classic sex allocation theory is challenging given the complex life histories and social interactions of species, hence it is likely that there are multiple mechanisms and selective forces dependent upon maternal and environmental drivers. Here, we show the previously demonstrated condition-dependent sex allocation in bridled nailtail wallabies (Onychogalea fraenata), where females in better condition were more likely to have sons, was reversed under high population densities and elevated maternal stress. In this solitary species, an elevated glucocorticoid stress response under unnaturally high densities likely influences adaptive sex allocation to the dispersive sex, consistent with the local resource competition theory. Managing factors such as population density, maternal stress, and food resources may be used to adjust offspring sex ratios in this endangered species.

Isoforms of the CD79 signal transduction component of the macropod B-cell receptor

B cell responses and their concomitant signal transduction pathways are not well understood in marsupial mammals, despite the availability of gene expression data for key immunoglobulin genes and for elements of the CD79a/CD79b heterodimer signalling complex for two model marsupials. Broader studies of factors that influence B cell responses are still hampered by a lack of species-specific reagents and there are few reports of other factors that influence gene expression such as the potential for splice variants in BCR components, which may influence immune signalling pathways. In this study, we characterise CD79a and CD79b genes in the endangered macropod marsupial, Onychogalea fraenata (the bridled nailtail wallaby) and show that domains and residues important for the structural and functional integrity of both monomers are conserved in this species, consistent with results previously reported for the closely-related macropod, Macropus eugenii (the tammar wallaby). We extend this work to report the detection of splice variants for CD79a and CD79b in wallaby species; three CD79a isoforms and one CD79b isoform. Of these, two CD79a isoforms and the CD79b isoform have not been reported in any other mammalian species.

Common species affects the utility of non-invasive genetic monitoring of a cryptic endangered mammal: The bridled nailtail wallaby

Non-invasive methods of monitoring wild populations (such as genotyping faeces or hair) are now widely used and advocated. The potential advantages of such methods over traditional direct monitoring (such as live capture) are that accuracy improves because sampling of non-trappable individuals may be possible, species in difficult and remote terrain can be surveyed more efficiently, and disturbance to animals is minimal. Few studies have assessed the effects of interactions between species on remote sampling success. We test the use of non-invasive monitoring for the cryptic, forest-dwelling, solitary and endangered bridled nailtail wallaby (Onychogalea fraenata) that is sympatric with the ecologically similar and more common black-striped wallaby (Macropus dorsalis). Six types of hair traps were tested for 3668 trap days, and hairs were caught with about a 10% success rate. Camera traps showed that baited hair traps targeted both wallaby species. We microscopically identified hair as bridled nailtail wallaby or black-striped wallaby. We compared these hairs and their genotypes (using seven microsatellite loci) with known bridled nailtail wallaby hairs and genotypes derived from animal trapping. Trapped bridled nailtail wallaby hairs had characteristics that could be mistaken for black-stripe wallaby hairs; characteristics were not diagnostic. Genetic assignment tests consistently differentiated the known bridled nailtail wallaby samples from identified black-striped wallaby samples, however genetic overlap between most of the microsatellite markers means that they are not suitable for species identification of single samples, with the possible exception of the microsatellite locus B151. With similar trapping effort and within the same area, live-capture mark-recapture techniques estimated 40-60 individuals and non-invasive methods only detected 14 genotypes. A species-specific genetic marker would allow more efficient targeting of bridled nailtail wallaby samples and increase capture rates.

Recovery of herbaceous species richness following herbicide treatment of Cenchrus ciliaris(buffel grass)- a pilot study of Onychogalea fraenata(Bridled nailtail wallaby) habitat restoration

Recovery of herbaceous species richness following herbicide treatment of Cenchrus ciliaris(buffel grass)- a pilot study of Onychogalea fraenata(Bridled nailtail wallaby) habitat restoration

Molecular identification and expression of Lyn tyrosine kinase isoforms in marsupials

Lyn is a tyrosine kinase molecule required for modulation of signalling cascades in cell populations including B lymphocytes of the mammalian immune system. We have characterised the coding domain of the marsupial lyn gene of two macropod marsupials; the Tammar Wallaby (Macropus eugenii) and the Bridled Nailtail Wallaby (Onychogalea fraenata) and show the co-expression of two Lyn isoforms in cells and tissues of these and three other marsupials (Brush-tail Possum, Trichosurus vulpecula; American Grey Short-tailed Opossum, Monodelphis domestica and Red-tailed Phascogale, Phascogale calura). The predicted Lyn proteins (LynA and LynB) were highly conserved across vertebrate species, with amino acid identities of 94% with their human orthologues and conservation of key tyrosine kinase motifs that suggests that marsupial Lyn most likely functions in cell signalling. Comparison of our cDNA data to annotations for Lyn transcripts (available through the Ensembl Genome Browser) for the Tammar Wallaby confirm splice sites for a number of exons in the wallaby transcript that are missing from the current annotation. This is the first report of the expression of kinase signalling molecules that influence immunity in metatherian mammals and provides key information to support ongoing studies of immune regulation in marsupials.

Establishment of an Endangered species on a private nature refuge: what can we learn from reintroductions of the bridled nailtail wallaby Onychogalea fraenata?

AbstractTranslocation and reintroduction are used to reduce extinction risk associated with a small population and range size in threatened mammal species. We evaluated the outcome of a reintroduction of the bridled nailtail wallaby Onychogalea fraenata to Avocet Nature Refuge, a private refuge in central Queensland, Australia. This macropod was also reintroduced to Idalia National Park in western Queensland in 1996 and occurs in one natural population in central Queensland. We estimated population growth, adult and juvenile survival, and distribution changes since the last release of O. fraenata to Avocet in 2005, and evaluated female reproductive success and health. Although animals were in good condition, population size was a tenth of that of the 1996 Idalia reintroduction reported after 3 years and, unlike at Idalia, juvenile survival at Avocet was low. The likely causes are consistent with predictors of translocation and reintroduction failures in mammals. These are predation, the small number of individuals in each release, the likely suboptimal health status of reintroduced individuals, drought, and possibly lack of dispersal from the small area of preferred habitat. The lessons of this reintroduction are that future attempts are likely to have the best chance of success if they occur in non-drought years, at sites with large, non-fragmented areas of brigalow forest, involve the release of large groups of animals together, and are accompanied by intensive, long-term baiting to control introduced predators.

Conservation and grazing in Australia’s north-east: the bridled nailtail wallaby

Australia’s vast continent is dominated by semi-arid and arid landscapes that have been modified to support the development of an extensive livestock grazing industry. Historically, this development has come at great environmental cost, with wide-scale landscape degradation and loss of biodiversity, including small macropods. With the growing appreciation of environmental values and ecological services provided by grazing landscapes, the engagement of pastoral landholders is now central to contemporary conservation efforts. In this paper we explore the spluttering recovery of Australia’s critically endangered bridled nailtail wallaby Onychogalea fraenata, once presumed extinct but now subject to a limited rehabilitation program in Queensland. We explore the ‘fit’ between management units and the scale of conservation challenges for the bridled nailtail wallaby, and then use this to frame the role of the private grazing industry in the governance of conservation actions. A centralised state conservation program has largely failed to stop the decline of the species, which remains critically endangered. We argue that non-state (privately) managed grazing properties working within a multi-level governance system that includes the state have a greater chance of conservation success because their actions can more appropriately match the scale of the problem at the implementation level. If the species recovers, the balance of management focus will need to shift towards broader scale actions such that localised disconnected sub-populations can successfully interbreed. By analysing the institutional failures that surround the bridled nailtail wallaby, we provide recommendations on how public institutions or policies can successfully catalyse private sector action at regional scales. These include avoiding economic incentives that may crowd out local stewardship, avoiding overly-authoritative state control (i.e. mono-centricity), and developing a multilevel governance structure that can strategically adapt its focus to the scale of various and shifting targets.

Dingoes affect activity of feral cats, but do not exclude them from the habitat of an endangered macropod

Context The loss of large predators has been linked with the rise of smaller predators globally, with negative impacts on prey species (mesopredator release). Recent studies suggest that the dingo, Australia’s top terrestrial predator, inhibits predation on native mammals by the invasive red fox, and therefore reduces mammal extinctions. Feral cats also have negative effects on native mammals, but evidence that dingoes suppress cats remains equivocal. Aims We sought to examine whether dingoes might spatially or temporally suppress the activity of feral cats at a site containing the sole wild population of an endangered macropod subject to feral cat predation (the bridled nailtail wallaby). Methods We used camera traps to compare coarse and fine-scale spatial associations and overlaps in activity times of mammals between August 2009 and August 2010. Key results Dingoes and cats used the same areas, but there was evidence of higher segregation of activity times during wet months. Potential prey showed no spatial avoidance of dingoes. Peak activity times of dingoes and their major prey (the black-striped wallaby) were segregated during the wetter time of year (December to March). We did not find evidence that cats were spatially excluded from areas of high prey activity by dingoes, but there was low overlap in activity times between cats and bridled nailtail wallabies. Conclusions These findings support the contention that fear of dingoes can sometimes affect the timing of activity of feral cats. However, cats showed little spatial avoidance of dingoes at a coarse scale. Implications Control of dingoes should not be abandoned at the site, because the potential moderate benefits of reduced cat activity for this endangered and geographically restricted wallaby may not outweigh the detrimental effects of dingo predation.

Scrub‐itch mite infestation in the endangered bridled nailtail wallaby

Skin lesions on the ears and inguinal and axillary regions of a number of adult animals within a captive population of the endangered bridled nailtail wallaby (Onychogalea fraenata) were associated with the trombiculid mite, Eutrombicula hirsti. The local inflammatory response of these Australian marsupials is described.

Optimal adaptive management for the translocation of a threatened species

Active adaptive management (AAM) is an approach to wildlife management that acknowledges our imperfect understanding of natural systems and allows for some resolution of our uncertainty. Such learning may be characterized by risky strategies in the short term. Experimentation is only considered acceptable if it is expected to be repaid by increased returns in the long term, generated by an improved understanding of the system. By setting AAM problems within a decision theory framework, we can find this optimal balance between achieving our objectives in the short term and learning for the long term. We apply this approach to managing the translocation of the bridled nailtail wallaby (Onychogalea fraenata), an endangered species from Queensland, Australia. Our task is to allocate captive-bred animals, between two sites or populations to maximize abundance at the end of the translocation project. One population, at the original site of occupancy, has a known growth rate. A population potentially could be established at a second site of suitable habitat, but we can only learn the growth rate of this new population by monitoring translocated animals. We use a mathematical programming technique called stochastic dynamic programming, which determines optimal management decisions for every possible management trajectory. We find optimal strategies under active and passive adaptive management, which enables us to examine the balance between learning and managing directly. Learning is more often optimal when we have less prior information about the uncertain population growth rate at the new site, when the growth rate at the original site is low, and when there is substantial time remaining in the translocation project. Few studies outside the area of optimal harvesting have framed AAM within a decision theory context. This is the first application to threatened species translocation.

Multi-scale patterns of habitat use by re-introduced mammals: A case study using medium-sized marsupials

Knowledge of the habitat requirements of threatened species at both local and landscape scales is crucial for maintaining viable populations and for making conservation and management decisions. Here, we use live trapping and radio-tracking to investigate habitat use by four species of threatened marsupials – burrowing bettongs ( Bettongia lesueur), brush-tailed bettongs ( B. penicillata), greater bilbies ( Macrotis lagotis), and bridled nailtail wallabies ( Onychogalea fraenata). The study populations had been re-introduced to Scotia Sanctuary in western New South Wales, Australia, within a predator-proof area. All showed preferences for particular macrohabitats while resting by day, with M. lagotis and B. penicillata selecting Eucalyptus woodland with Triodia understorey and B. lesueur and O. fraenata selecting Eucalyptus woodland with shrubs. However, they showed no such partiality at night. Bettongia penicillata used areas with Triodia and litter but few herbs for shelter, while burrows of M. lagotis avoided shrubs. Habitat components that influenced trap captures were: crust cover and herb layer cover (negative) for B. penicillata, trees <5 m in height and number of shrubs (both negative) for B. lesueur, crust cover for M. lagotis, and crust cover and trees <5 m high for O. fraenata (both negative). There was also a negative association at this scale between B. penicillata and both B. lesueur and M. lagotis, suggesting the possibility of competition. Our results support the idea that studies at multiple spatial scales are crucial to understand the habitat use and requirements of threatened fauna, and should therefore be incorporated into future re-introduction programs.