The University of New South Wales
- School of Biological, Earth and Environmental Sciences (BEES)
- Research Officer
Research Items (4)
- Feb 2019
Natal dispersal is influenced by many environmental and biological factors and can be a time of elevated mortality risk. We aimed to understand how physical, behavioral, and demographic traits of mothers and juveniles influenced natal dispersal by studying a population of brushtail possums (Trichosurus vulpecula) reintroduced to their former range. We used radiotracking and trapping to intensively monitor the growth, survival, shelter use, and movement of juveniles and their mothers from pouch young to adulthood over a 22-month study period. We recorded multiple dispersal movement phases, with males undergoing more phases than females (6 versus 4) and dispersing 16 times farther. Dispersal age was positively related to maternal body mass for males but not females. Mothering behavior varied with offspring sex, with mothers tending to shelter daughters in a higher proportion of new shelter sites compared to sons. Females matured at a younger age and mass than males, and possums that left their mother at an earlier age reached sexual maturity earlier, regardless of sex. The timing of dispersal by males was not influenced by body mass, age, sexual maturity, rainfall, or the age of their younger sibling. Survival of juveniles (63%) was not related to sex or dispersal phase but instead sexual maturity, suggesting an effect of experience. Sex, maternal effects, and an interaction between the two influenced the development and movement of juvenile possums, suggesting that at least some sex-related differences in natal dispersal may be influenced by the mother rather than simply being the innate behavior of offspring. Although sex effects on dispersal have been reported in marsupials, the interaction with maternal characteristics has been previously overlooked.
- Dec 2018
Context: Predator-controlled environments can lead to prey species losing costly antipredator behaviours as they exploit their low-risk environment, creating a ‘predator-naïve’ population. If individuals lacking suitable antipredator behaviours are used as source populations for reintroductions to environments where predators are present, their behaviour could result in high post-release predation. In contrast, animals sourced from environments with predators (‘predator-exposed’) may show effective antipredator behaviours and thus higher survival post-release. Aims: The aim was to compare the antipredator behaviour of brushtail possums (Trichosurus vulpecula) at predator-exposed and predator-naïve source populations, and then compare post-release survival after their reintroduction to a low predator environment. Methods: Data were collected from possums at two sites, one with and one without mammalian predators. The behavioural responses of possums to a spotlighter, their willingness to use supplementary feeders at ‘safe’ and ‘risky’ heights, whether they avoided predator odour at traps and their general willingness to enter traps were recorded. Key results: Predator-naïve possums showed weaker antipredator responses, were often found at ground level, engaged with novel objects, did not avoid predator scents and utilised different habitats regardless of associated predation risk. In contrast, predator-exposed possums had higher antipredator responses, chose connected trees, were rarely found at ground level and were generally difficult to capture. Post-translocation survival was high for both source populations. Predator-naïve-sourced female possums began to avoid predator urine (feral cat; Felis catus) 12 months after translocation. Conclusions: Our research demonstrates that environmental predation risk can predict prey naïvety in brushtail possums. Some aspects of prey naïvety behaviour appear to be able to change in response to altered predation risk. Implications: With many threatened species now existing only in feral predator-free areas, these results have implications for future reintroductions into unbounded areas where feral predators are present, and for the management of fenced reserves. The addition of a small number of predators to fenced reserves may aid in retaining antipredator behaviours in fenced prey populations.
- May 2018
Release methods can influence the outcome of reintroductions. We tested the effect of delayed, immediate and supplementary food/shelter release treatments on the reintroduction of brushtail possums Trichosurus vulpecula to an environment in which introduced predators, particularly foxes, were subject to control. Monitoring of 48 radio-collared possums over 3 months revealed that immediate release possums settled into a stable range significantly faster than other groups, but there were no differences in survival, dispersal distance, reproduction or body condition. Ten days after release possums from all treatment groups had lost body mass, but by day 60 most were heavier than at the time of translocation. After release, possums sometimes used shelter sites easily accessible to predators, but within 3 weeks they regularly selected safer shelter. Risky shelter selection and loss of condition immediately after release suggests that supplementary food and shelter could be beneficial, but supportive measures were rarely used or did not have the desired effect. In an environment with higher predator densities, risky shelter selection could lead to high post-release predation, and mass loss could encourage animals to forage in riskier ways, further increasing vulnerability. In these environments effective uptake of supplementary food and shelter could reduce predation risk, but supplementary measures would need to be presented in a way that maximises uptake. In contrast, if post-release predation risk is low then supportive measures may not be required. Innovative methods for providing post-release support should continue to be developed for reintroductions to areas where supportive measures are needed.
- Jan 2016
Broad-scale Australian mammal declines following European settlement have resulted in many species becoming regionally or globally extinct. Attempts to reintroduce native mammals are often unsuccessful due to a suboptimal number of founders being used, high rates of predation and a lack of knowledge of the reintroduction biology for the species concerned. We trialled predator swamping and supplementary feeding in an attempt to offset predation and improve reintroduction success for the burrowing bettong (Bettongia lesueur) in arid South Australia. We compared population longevity of a large release group (1266 animals) with five releases of smaller groups (∼50 animals at each). We compared release sites with (n≤5) and without (n≤1) supplementary food to determine whether site fidelity, body condition and reproduction were affected, and whether these traits aided population establishment. Predator swamping did not facilitate reintroduction success, with no bettongs detected more than 122 days after release. While supplementary food increased site fidelity and persistence at release sites, bettongs failed to establish successfully at any site. Neither predator swamping nor supplementary feeding enhanced reintroduction success at our sites but results suggested that supplementary feeding should be explored as an aid to reintroduction success for Australian mammals.