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.
Habitat degradation contributes to species decline, and habitat quality is an important factor influencing reintroduction success globally. Habitat quality can include a range of physical resources such as nest sites and food resources but also anything that can restrict the use of these resources such as predation risk or competition. In arid Australia, introduced predators are thought to be the primary cause of mammal extinction and reintroduction failure although habitat clearance and alteration are also major causes of population decline. Common brushtail possums are one arid Australian marsupial close to regional extinction. To understand whether habitat quality was limiting their recovery, we reintroduced 148 possums into an area where introduced red foxes were controlled but historic overgrazing had degraded the habitat. We measured both direct (hollow availability, midstorey cover and high‐quality plant foods) and indirect (survival, condition, reproduction, movement) measures of habitat quality. Sixty‐seven released possums and 26 post‐release recruits were radiocollared for up to 2 years after release. Post‐release survival of radiocollared possums was high after 12 months (0.70), and there were no deaths from starvation. Predation by feral cats was the most common cause of mortality, and the open, degraded habitat may have exacerbated predation risk. Continuous breeding, good body condition and comparative home ranges with other sites suggested that food resources were not limiting. Possums used natural tree hollows in Eucalyptus spp. with no use of artificial nest boxes. Results suggest that historically degraded habitat was not a barrier to short‐term reintroduction success when foxes were controlled and natural tree hollows were plentiful. However, demographic data on hollow‐bearing tree species suggest a possible future decline in availability of hollows. These factors, combined with the unknown effects of drought, and synergistic effects of predation and poor quality habitat, suggest long‐term reintroduction success may require improved habitat and cat control.
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.
Conservation practitioners implement management interventions for the protection of threatened species, but the benefits are rarely measured. We investigated the efficacy of aerial poison baiting for feral cats, a species identified as a threat to reintroduced populations of two Australian mammals. We measured individual survival, short‐term changes in activity and longer term population trajectories in cats and reintroduced western quolls and brushtail possums before and after annual baiting events. Between 87% and 100% of radiocollared feral cats that remained in the baited area died from poisoning in 2017, 2018 and 2019. Camera detection rates significantly declined after each event (40–77%), and the proportion of cameras occupied remained lower after baiting commenced (20–60% before vs. <20% after). Cat decline on cameras was significantly higher in areas with low rabbit abundance, suggesting controlling alternative prey would improve baiting success. Importantly, none of 37 radiocollared quolls died from poisoning despite pre‐baiting trials determining that they were the most common species removing baits (26%). We detected no negative impact of baiting on the quoll and possum populations but could not demonstrate a significant net benefit. Trapping data suggested no change in annual quoll survival after baiting despite a slight increase in survival of radiocollared quolls. Quoll detection rates on camera did not significantly decline after each baiting event. A decline in the last two years of monitoring was possibly due to drought conditions. Approximately 10% of radiocollared possums died from poisoning after the first baiting event, but trapping and camera detections suggested a stable or increasing population. Poison baiting successfully reduced cat abundance, and there was no measurable negative effect on populations of reintroduced species. Long‐term monitoring through a range of seasonal conditions is required to determine the net benefit of predator control for reintroduced populations where paired impact and control sites are impractical.
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