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.
ContextThe niche reduction hypothesis (NRH) predicts that the realised niche of declining species is reduced by threats that are mediated by environmental, biotic and evolutionary processes, explaining why species decline in some locations but not others. The critically endangered central rock-rat (CRR) survives only in rugged mountain range habitat in central Australia and is highly vulnerable to cat predation. We predicted that cat density and ranging behaviour, and, hence, predation risk, is mediated by habitat complexity, thus explaining the mechanism maintaining the CRR refuge. AimsWe sought to determine whether cat densities were lower in the rugged CRR refuge than in an adjacent valley dominated by less complex rocky habitats and no longer occupied by CRRs. MethodsWe installed arrays of camera traps along two parallel mountain ranges in the refuge and in the intervening valley habitats. We identified uniquely patterned individual cats and compared spatially explicit capture–recapture (SECR) models to evaluate our hypothesis that cat density varies with topographic complexity. Key resultsThe dominant effect in all models was the significant negative relationship between cat detection probability and fine-scale topographic ruggedness. Two of the best three SECR models indicated lower cat densities and relative home-range sizes in the refuge than in the valley. In total, 17% of cats were detected in both habitat types. ConclusionsWe found some evidence that cat density and home-range size were mediated by habitat complexity. Further, the negative relationship between cat detection probability and topographic complexity suggests that cats spend less time foraging in CRR refuge habitat. ImplicationsCat management programs, aimed at reducing predation pressure on the CRR, must include the refuge and surrounding habitats to control cats that pose a threat to CRR subpopulations.
We monitored faecal glucocorticoid metabolites (FGM) in 53 western quolls following capture. Using this stressor, we validated an assay for monitoring FGM in quolls. On average, FGM peak 24 hours after capture. Females exhibit higher baseline and peak FGM levels than males. Individuals vary in their physiological response to capture.
Predator diet can be influenced by competition and intraguild predation, leading to resource partitioning and/or avoidance. For sympatric, endemic predators, these processes form as predator species coevolve, facilitating coexistence. However, when novel predator interactions occur, significant dietary overlap could create acute levels of competition leading to intraguild predation and population extinction, or accelerated changes in diet and/or spatial and temporal avoidance. We measured diet, intraguild predation, and spatial and temporal overlap in two predator species in a novel predator interaction: the western quoll (Dasyurus geoffroii), a small, native carnivore reintroduced to semi-arid Australia, and the domestic cat (Felis catus), a larger introduced carnivore already resident at the release site. Both species exhibited high dietary overlap and fed on mammals, reptiles, birds, and invertebrates. Cats included quolls in their diet. Quoll diet was broader (including carrion, bats, and plant material) and flexible, changing significantly with age, sex, and season. Introduced rabbit was the most common prey item recorded for both species (frequency of occurrence = 40–50%). However, quolls consumed rabbits in relation to their availability while rabbit consumption in cats was unrelated to availability suggesting a stronger dependence on rabbit prey. Quoll diet did not change over time since release and they did not spatially or temporally avoid cats. However, cats were significantly spatially associated with rabbits while quolls were not, suggesting higher predation efficacy in quolls possibly due to their smaller body size enabling them to catch rabbits inside warrens. Despite high dietary overlap and intraguild predation, the quoll’s broad and flexible diet and high predation efficacy appeared to assist in facilitating coexistence and reducing competition in this novel predator interaction. This dietary flexibility may be harnessed to improve conservation outcomes: reducing introduced rabbits in our study area could naturally reduce feral cat populations while having less impact on native quolls.
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