A triple threat: high population density, high foraging intensity and flexible habitat preferences explain high impact of feral cats on prey.

Invasive mammalian predators are linked to terrestrial vertebrate extinctions worldwide. Prey naïveté may explain the large impact invasive predators have on native prey; prey may fail to detect and react appropriately to the cues of novel predators, which results in high levels of depredation. In Australia, the feral cat (Felis catus) and the red fox (Vulpes vulpes) are implicated in more than 30 animal extinctions and the naïveté of native prey is often used to explain this high extinction rate. Reptiles are one group of animals that are heavily preyed upon by F. catus and V. vulpes. However, very few studies have examined whether reptiles are naive to their cues. In this study, we examine the ability of two native reptile species (Morethia boulengeri and Christinus marmoratus) to detect and distinguish between the chemical cues of two invasive predators (V. vulpes and F. catus) and three native predators (spotted-tailed quoll, Dasyurus maculatus; dingo, Canis lupus dingo; eastern brown snake, Pseudonaja textilis), as well as two non-predator controls (eastern grey kangaroo, Macropus giganteus and water). We conducted experiments to quantify the effects of predator scents on lizard foraging (the amount of food eaten) during 1 h trials within Y-maze arenas. We found both study species reduced the amount they consumed when exposed to predator scents—both native and invasive—indicating that these species are not naive to invasive predators. An evolved generalized predator-recognition system, rapid evolution or learned behaviour could each explain the lack of naïveté in some native Australian reptiles towards invasive predators.

Context Home-range size and population density characteristics are crucial information in the design of effective wildlife management, whether for conservation or control, but can vary widely among populations of the same species. Aims We investigate the influence of site productivity on home-range size and population density for Australian populations of the native, threatened spotted-tailed quoll (Dasyurus maculatus) and the alien and highly successful feral cat (Felis catus). Methods We use live trapping and fine-scale GPS tracking to determine the home-range size and population density for both species across five sites in Tasmania. Using these data, as well as published estimates for both species from across Australia, we model how these parameters change in response to productivity gradients. We also use the telemetry data to examine the energetic costs of increasing home-range size for both species. Key results For both species, decreasing site productivity correlates with lower population density, and in spotted-tailed quolls and female feral cats, it also correlates with larger home-range sizes. However, the relative magnitude of these changes is different. Feral cats show smaller increases in home-range size but larger decreases in population density relative to spotted-tailed quolls. Our results suggest that these differences may be because increases in home-range size are more costly for feral cats, demonstrated by larger increases in nightly movement for the same increase in home-range area. Conclusions We suggest that knowledge of both home-range size and population density is needed to accurately determine how species respond to habitat productivity, and inform effective management across their geographic range. Implications These results have clear management implications; for example, in our low-rainfall sites, an adult female spotted-tailed quoll requires up to five times the amount of habitat expected on the basis of previous studies, thus dramatically increasing the costs of conservation programs for this threatened native species. Conversely, productivity-driven differences of up to four-fold in feral cat population density would influence the resources required for successful control programs of this invasive species.

Research and management attention on the impacts of the introduced domestic cat (Felis catus) on Australian fauna have focussed mainly on the feral population. Here, we summarise the evidence for impacts of predation by pet cats on Australian wildlife. We collate examples of local wildlife population decline and extirpation as a result, at least in part, of predation by pet cats. We assemble information across 66 studies of predation by pet cats worldwide (including 24 Australian studies) to estimate the predation toll of pet cats in Australia, plus the predation pressure per unit area in residential areas. We compared these estimates to those published for feral cats in Australia. The per capita kill rate of pet cats is 25% that of feral cats. However, pet cats live at much higher densities, so the predation rate of pets per square kilometre in residential areas is 28–52 times larger than predation rates by feral cats in natural environments, and 1.3–2.3 times greater than predation rates per km2 by feral cats living in urban areas. Pet cats kill introduced species more often than do feral cats living in natural environments, but, nonetheless, the toll of native animals killed per square kilometre by pet cats in residential areas is still much higher than the toll per square kilometre by feral cats. There is no evidence that pet cats exert significant control of introduced species. The high predation toll of pet cats in residential areas, the documented examples of declines and extirpations in populations of native species caused by pet cats, and potential pathways for other, indirect effects (e.g. from disease, landscapes of fear, ecological footprints), and the context of extraordinary impacts from feral cats on Australian fauna, together support a default position that pet cat impacts are serious and should be reduced. From a technical perspective, the pet cat impacts can be reduced more effectively and humanely than those of feral cats, while also enhancing pet cat welfare. We review the management options for reducing predation by pet cats, and discuss the opportunities and challenges for improved pet cat management and welfare.

Wildlife disease ecology in changing landscapes: Mesopredator release and toxoplasmosis

Supplementary material from "A triple threat: high population density, high foraging intensity and flexible habitat preferences explain high impact of feral cats on prey"

Predation by feral cats (Felis catus) and red foxes (Vulpes vulpes) are key threatening processes for many endangered wildlife species. Toxin delivery through compulsive oral grooming is a potential mechanism to supplement existing control techniques for feral cats and red foxes, particularly when high prey densities reduce the uptake of toxic food baits by cats. We investigated the efficacy of different grooming traps by applying a gel containing toxic para-aminopropiophenone (PAPP) to the fur of feral cats and red foxes in experimental pens. Grooming behaviour and signs of poisoning in these animals were recorded by video. More cats interacted with “walk past” grooming traps triggered by sensor beams than with trap models that required the cat to enter a pipe or baited cage. After triggering a trap that had applied PAPP gel to their fur, 14 of 16 feral cats showed symptoms of anoxia, and 8 of these cats were dead by the following morning without exhibiting signs of distress. Seven of 12 foxes were observed to groom fur to which toxic gel had been applied and 3 of these ingested a lethal quantity of PAPP as a result. Our successful proof-of-concept trials support further development of grooming trap sensors and toxin delivery mechanisms to provide humane and targeted feral cat control, although this technique is unlikely to be as successful for fox control, given that foxes appear to not groom as fastidiously as cats.

Context Camera traps have become a crucial tool for monitoring predators and are frequently deployed with lures to boost detection. Feral cats, a problematic invasive species in Australia, are commonly monitored using camera traps with lures. Despite the additional effort required for lure deployment, it remains unclear which lures are effective for monitoring feral cats. Aims Our study aimed to address this knowledge gap and assess the impact of various lure treatments on feral cat detection and activity. We also examined the response of other predators, such as Tasmanian devils and spotted-tailed quolls, to the lures and explored how their activity influenced feral cat visitation. Methods We deployed food, olfactory and visual lures, along with a null treatment across four grids of 16 camera traps over a period of 4 months in south-eastern Tasmania. Key results We observed increased feral cat detection with food (odds ratio = 3.69, 97.5% CI = 1.04, 13.2) and visual lures (odds ratio = 5.95, CI = 1.75, 20.2), but not olfactory lures (odds ratio = 1.88, CI = 0.55, 6.51). Examining only sites where cats were detected, food (odds ratio = 3.35, CI = 1.27, 8.9), visual (odds ratio = 3.39, CI = 1.41, 8.1) and olfactory (odds ratio = 2.7, CI = 1.02, 7.1) lures all increased feral cat visitation to the camera traps. Tasmanian devil and spotted-tailed quoll activity increased 4.85-fold (CI = 2.89, 8.1) and 4.94-fold (CI = 2.92, 8.4) when using the food lure, and 4.24-fold (CI = 2.5, 7.2) and 3.49-fold (CI = 2.03, 6.0) when using the olfactory lure. Whereas a positive relationship existed between devil and cat activity overall (β = 0.49, s.e. = 0.15, P ≤ 0.001), negative associations were found between devil and cat activity in the presence of food (β = −0.36, s.e. = 0.19, P = 0.057) and olfactory (β = −0.42, s.e. = 0.20, P = 0.026) lures. Conclusions Our findings demonstrated the effectiveness of lures in temperate environments for feral cat monitoring but highlighted potential interspecific interactions that reduce feral cat visitation. Implications We recommend a thoughtful consideration of the environment and resident species to ensure effective lure use and to minimise unintended negative influences on the capture of target species.

In ecosystems, some organisms facilitate others indirectly, by interacting with one or more common mediator organisms. Thus, the indirect effects of introducing or removing species can be resonant, sometimes leading to successional extinctions. The dingo (Canis dingo) is the apex predator in Australian deserts and was introduced to the continent between 3000 and 5000 years ago. Dingoes suppress the abundances of introduced mesopredators, the red fox (Vulpes vulpes) and feral cat (Felis catus) and in so doing mitigate small mammal declines wreaked by these mesopredators. Given the positive association between the abundances of dingoes and small mammals, we predicted that dingoes indirectly facilitate a specialised native predator of small mammals, the Barn owl, Tyto alba. We tested our prediction by monitoring the abundances of dingoes, foxes, cats, small mammals and barn owls and investigating barn owl diets in areas where dingoes were common versus areas where dingoes were functionally extinct on either side of the dingo barrier fence (DBF) in the Strzelecki Desert. Foxes and cats were less abundant in areas where dingoes were common. Conversely, small mammals and barn owls were more abundant where dingoes were common. Owls in areas where dingoes were common fed almost exclusively on small mammals, but owls in areas where dingoes were functionally extinct fed on greater proportion of birds and invertebrates. The findings of our study provide evidence that an introduced apex predator may indirectly facilitate a native predator and illustrates the myriad of far-reaching indirect effects that can result from apex predator suppression.

ContextSignificant resources have been devoted to the control of introduced mesopredators in Australia. However, the control or removal of one pest species, such as, for example, the red fox (Vulpes vulpes), may inadvertently benefit other invasive species, namely feral cats (Felis catus) and rabbits (Oryctolagus cuniculus), potentially jeopardising native-species recovery. AimsTo (1) investigate the impact of a large-scale, long-term fox-baiting program on the abundance of foxes, feral cats and introduced and native prey species in the Flinders Ranges, South Australia, and (2) determine the effectiveness of a short time period of cat removal in immediately reducing feral cat abundance where foxes are absent. MethodsWe conducted an initial camera-trap survey in fox-baited and unbaited sites in the Flinders Ranges, to quantify the impact of fox baiting on the relative abundance of foxes, feral cats and their prey. We then conducted a secondary survey in sites where foxes were absent, following an intensive, but short, time period of cat removal, in which 40 cats were shot and killed. Key resultsNo foxes were detected within baited sites, but were frequently detected in unbaited sites. We found a corresponding and significant increase in several native prey species in fox-baited sites where foxes were absent. Feral cats and rabbits were also more frequently detected within baited sites, but fox baiting did not singularly predict the abundance of either species. Rather, feral cats were less abundant in open habitat where foxes were present (unbaited), and rabbits were more abundant within one predominantly open-habitat site, where foxes were absent (fox-baited). We found no effect of short-term cat removal in reducing the local abundance of feral cats. In both camera-trap surveys, feral cat detections were positively associated with rabbits. ConclusionsLong-term fox baiting was effective in fox removal and was associated with a greater abundance of native and introduced prey species in the Flinders Ranges. To continue to recover and conserve regional biodiversity, effective cat control is required. ImplicationsOur study showed fox removal has likely resulted in the local release of rabbits and an associated increase in cats. Because feral cat abundance seemingly fluctuated with rabbits, we suggest rabbit control may provide an alternative and more effective means to reduce local feral cat populations than short-term removal programs.

Invasive predators have severe impacts on global biodiversity, and their effects in Australia have been more extreme than on any other continent. The spotted‐tailed quoll (Dasyurus maculatus), an endangered marsupial carnivore, coexists with three eutherian carnivores, the red fox (Vulpes vulpes), feral cat (Felis catus) and wild dog (Canis lupus ssp.) with which it did not coevolve. No previous study has investigated dietary overlap between quolls and the suite of three eutherian carnivores. By analysing scats, we aimed to quantify dietary overlap within this carnivore assemblage in eastern Australia, and to detect any differences that may facilitate coexistence. We also sought evidence of intraguild predation. Dietary overlap between predators was extensive, with the greatest similarity occurring between foxes and cats. However, some differences were apparent. For example, cats mainly consumed smaller prey, and wild dogs larger prey. Quolls showed greater dietary overlap with foxes and cats than with dogs. Intraguild predation was evident, with fox remains occurring in 3% of wild dog scats. Our results suggest wild dogs competitively dominate invasive foxes, which in turn are likely to compete with the endangered quoll.

Context The Felixer grooming device (‘Felixer’) is a lethal method of feral cat control designed to be cost-effective and target specific. Aims This study aims to test the target specificity of the Felixer in Tasmania, with a particular focus on Tasmanian devil and quoll species due to the overlap in size, habitats and behaviour between these native carnivores and feral cats. Methods Our study deployed Felixer devices set in a non-lethal mode in nine field sites in Tasmania, one field site in New South Wales and two Tasmanian wildlife sanctuaries. Key results Our study recorded 4376 passes by identifiable vertebrate species including 528 Tasmanian devil passes, 507 spotted-tailed quoll passes and 154 eastern quoll passes. Our data showed that the Felixer can successfully differentiate quoll species from feral cats with spotted-tailed quolls and eastern quolls targeted in 0.19% and 0% of passes, respectively. However, Tasmanian devils and common wombats were targeted in 23.10% and 12% of passes, respectively, although sample size was low for common wombats (n = 25). Conclusions The Felixer could not reliably identify Tasmanian devils and possibly common wombats as non-target species. Further data is needed to confirm the potential for impacts on the common wombat and other potential non-target species in Tasmania, and the likelihood of the toxin being ingested by falsely targeted individuals. Implications Our study suggest that the Felixer device is safe for use in the presence of two species of conservation concern, the eastern and spotted-tailed quoll. It also supports evidence from previous studies that the Felixer is unlikely to impact bettongs and potoroos. Use of Felixer devices across much of Tasmania would have to balance the conservation or economic benefits of cat control against potential impacts on Tasmanian devils. We suggest that active Felixer deployments be preceded by surveys to establish the range of species present at the control site, and the season of control considered carefully to minimise potential impacts on more susceptible juvenile animals. In addition, modifications to the Felixer device such as the proposed incorporation of AI technology should be tested against the Tasmanian devil and other non-target species.

Context Invasive mammalian predators have caused population declines and extinctions of wildlife worldwide. Many of these species exhibit some form of prey naïveté, which heightens their vulnerability to novel predators. In Australia, introduced feral cats (Felis catus) and red foxes (Vulpes vulpes) have had a particularly negative effect on native fauna, with the impacts of cats on mammals and birds well documented. Although feral cats are known to regularly prey on Australian reptiles, little is known about the behavioural responses of reptiles to cats, including whether native reptiles can recognise cats as a predation risk, and if so, which cues they use. Aims We investigated behavioural responses of two Australian lizard species, the shrubland morethia skink (Morethia obscura) and eastern striped skink (Ctenotus robustus), to the visual cues of feral cats in semiarid, south-eastern Australia. Methods We used arena trials to test lizards for predator recognition by using visual cues of an alien mammal predator (taxidermied cat, Felis catus), a native mammal predator (taxidermied western quoll, Dasyurus geoffroyi) and a mammal non-predator (taxidermied European rabbit, Oryctolagus cuniculus), as well as a procedural control (bucket) and a negative control (nothing). Key results We found little evidence of behavioural change when lizards were exposed to the taxidermied cat. Morethia obscura basked less when exposed to all treatments and C. robustus increased vigilance when in the presence of the taxidermied cat, but overall responses were similar among treatments. Conclusions Our findings suggest that stationary visual cues of cats do not trigger behavioural responses in these two lizard species. Implications Future research should assess behavioural responses to combinations of cat cues (e.g. movement, scent). Developing a deeper understanding of predator recognition systems and prey naïveté in reptile communities will be crucial for conservation of Australian reptiles that are negatively affected by feral cats.

Feral cats (Felis catus) are one of the world’s worst invasive species with continuing expanding populations, particularly in urban areas. Effects of anthropogenic changing land-use, especially urbanisation, can alter distribution and behaviour of feral cats. Additionally, resource availability can influence home range and habitat use. Therefore, we investigated home range and habitat use of feral cats (n = 11) in an urban mosaic with varying degrees of urbanisation and green spaces in Pietermaritzburg, KwaZulu-Natal, South Africa. Using global positioning cellular trackers, individual feral cats were followed for a minimum of six months. Minimum convex polygons (MCP) and kernel density estimates (KDE) were used to determine their home range, core area size, and habitat use. Mean home range (± SE) for feral cats was relatively small (95% MCP 6.2 ± 4.52 ha) with no significant difference between male and female home ranges, nor core areas. There was individual variation in home ranges despite supplemental feeding in the urban mosaic. Generally supplemental resources were the primary driver of feral cat home ranges where these feeding sites were within the core areas of individuals. However, the ecological consequences of feeding feral cats can increase their survival, and reduce their home ranges and movement as found in other studies.

Evaluation of physiological stress in Australian wildlife: Embracing pioneering and current knowledge as a guide to future research directions

We tested whether mountain pine beetles Dendroctonus ponderosae , an insect herbivore that exhibits outbreak population dynamics, modifies its habitat selection behaviour in response to density‐dependent environmental shifts. Using an individual‐based habitat selection model, we formulated predictions of how beetle population density will influence breeding habitat selectivity. Our model predicted that beetles should be more selective at intermediate densities than at low or high densities. The mechanisms influencing optimal selectivity differed between low and high density populations. In low density populations, breeding site availability was the primary factor affecting selectivity, whereas intraspecific competition and the reliability of habitat quality cues were important in high density populations. We tested our model predictions in natural populations that encompassed a range of beetle population densities. Our empirical findings supported the two key predictions from our model. First, habitat quality was more variable in high density populations. Second, individuals in high density populations were less selective compared to beetles from intermediate density populations. Our results demonstrate that beetles alter their habitat selection behaviour in response to density‐dependent shifts. We propose that the behavioural changes we identified may influence the rate at which beetle populations transition between density states.