A global synthesis and assessment of free-ranging domestic cat diet

Free-ranging cats (Felis catus) are globally distributed invasive carnivores that markedly impact biodiversity. Here, to evaluate the potential threat of cats, we develop a comprehensive global assessment of species consumed by cats. We identify 2,084 species eaten by cats, of which 347 (16.65%) are of conservation concern. Islands contain threefold more species of conservation concern eaten by cats than continents do. Birds, reptiles, and mammals constitute ~90% of species consumed, with insects and amphibians being less frequent. Approximately 9% of known birds, 6% of known mammals, and 4% of known reptile species are identified in cat diets. 97% of species consumed are <5 kg in adult body mass, though much larger species are also eaten. The species accumulation curves are not asymptotic, indicating that our estimates are conservative. Our results demonstrate that cats are extreme generalist predators, which is critical for understanding their impact on ecological systems and developing management solutions.

Heterogeneous patterns of heterozygosity loss in isolated populations of the threatened eastern barred bandicoot (Perameles gunnii)

Identifying and analysing isolated populations is critical for conservation. Isolation can make populations vulnerable to local extinction due to increased genetic drift and inbreeding, both of which should leave imprints of decreased genome-wide heterozygosity. While decreases in heterozygosity among populations are frequently investigated, fewer studies have analysed how heterozygosity varies among individuals, including whether heterozygosity varies geographically along lines of discrete population structure or with continuous patterns analogous to isolation by distance. Here we explore geographical patterns of differentiation and individual heterozygosity in the threatened eastern barred bandicoot (Perameles gunnii) in Tasmania, Australia, using genomic data from 85 samples collected between 2008 and 2011. Our analyses identified two isolated demes undergoing significant genetic drift, and several areas of fine-scale differentiation across Tasmania. We observed discrete genetic structures across geographical barriers and continuous patterns of isolation by distance, with little evidence of recent or historical migration. Using a recently developed analytical pipeline for estimating autosomal heterozygosity, we found individual heterozygosities varied within demes by up to a factor of two, and demes with low-heterozygosity individuals also still contained those with high heterozygosity. Spatial interpolation of heterozygosity scores clarified these patterns and identified the isolated Tasman Peninsula as a location where low-heterozygosity individuals were more common than elsewhere. Our results provide novel insights into the relationship between isolation-driven genetic structure and local heterozygosity patterns. These may help improve translocation efforts, by identifying populations in need of assistance, and by providing an individualised metric for identifying source animals for translocation.

Effects of different management strategies on long-term trends of Australian threatened and near-threatened mammals

Monitoring is critical to assess management effectiveness, but broadscale systematic assessments of monitoring to evaluate and improve recovery efforts are lacking. We compiled 1808 time series from 71 threatened and near-threatened terrestrial and volant mammal species and subspecies in Australia (48% of all threatened mammal taxa) to compare relative trends of populations subject to different management strategies. We adapted the Living Planet Index to develop the Threatened Species Index for Australian Mammals and track aggregate trends for all sampled threatened mammal populations and for small (<35 g), medium (35-5500 g), and large mammals (>5500 g) from 2000 to 2017. Unmanaged populations (42 taxa) declined by 63% on average; unmanaged small mammals exhibited the greatest declines (96%). Populations of 17 taxa in havens (islands and fenced areas that excluded or eliminated introduced red foxes [Vulpes vulpes] and domestic cats [Felis catus]) increased by 680%. Outside havens, populations undergoing sustained predator baiting initially declined by 75% but subsequently increased to 47% of their abundance in 2000. At sites where predators were not excluded or baited but other actions (e.g., fire management, introduced herbivore control) occurred, populations of small and medium mammals declined faster, but large mammals declined more slowly, than unmanaged populations. Only 13% of taxa had data for both unmanaged and managed populations; index comparisons for this subset showed that taxa with populations increasing inside havens declined outside havens but taxa with populations subject to predator baiting outside havens declined more slowly than populations with no management and then increased, whereas unmanaged populations continued to decline. More comprehensive and improved monitoring (particularly encompassing poorly represented management actions and taxonomic groups like bats and small mammals) is required to understand whether and where management has worked. Improved implementation of management for threats other than predation is critical to recover Australia's threatened mammals.

Addressing prey naivety in native mammals by accelerating selection for antipredator traits

Harnessing natural selection to improve conservation outcomes is a recent concept in ecology and evolutionary biology and a potentially powerful tool in species conservation. One possible application is the use of natural selection to improve antipredator responses of mammal species that are threatened by predation from novel predators. We investigated whether long-term exposure of an evolutionary naïve prey species to a novel predator would lead to phenotypic changes in a suite of physical and behavioral traits. We exposed a founder population of 353 burrowing bettongs (Bettongia lesueur) to feral cats (Felis catus) over 5 years and compared the physical and behavioral traits of this population (including offspring) to a control (non-predator exposed) population. We used selection analysis to investigate whether changes in the traits of bettongs were likely due to phenotypic plasticity or natural selection. We also quantified selection in both populations before and during major population crashes caused by drought (control) and high predation pressure (predator-exposed). Results showed that predator-exposed bettongs had longer flight initiation distances, larger hind feet, and larger heads than control bettongs. Trait divergence began soon after exposure and continued to intensify over time for flight initiation distance and hind foot length relative to control bettongs. Selection analysis found indicators of selection for larger hind feet and longer head length in predator-exposed populations. Results of a common garden experiment showed that the progeny of predator-exposed bettongs had larger feet than control bettongs. Results suggest that long-term, low-level exposure of naïve prey to novel predators can drive phenotypic changes that may assist with future conservation efforts.

pH-Responsive Polymer Implants for the Protection of Native Mammals: Assessment of Material Properties and Poison Incorporation on Performance

Efforts to mitigate the effects of feral cats through the management of remnant or reintroduced populations of threatened species, are often unsuccessful due to predation by control-averse feral cats, or 'problem individuals'. In order to target these animals, we have developed the Population Protecting Implant (PPI). PPIs are designed to be implanted subcutaneously in a native animal. If the animal is preyed upon, and the implant ingested by a feral cat, release of a toxic payload is triggered in the acidic stomach environment and the problem individual is eliminated. We introduce the first toxic implant incorporating the poison sodium fluoroacetate. Manufactured via fluidised-bed spray coating, toxic implants exhibited uniform reverse enteric coatings and low intra-batch variation. Toxic implants were found to exhibit favourable stability at subcutaneous pH in vitro, and rapidly release their toxic payload in vitro at gastric pH. However, limited stability was demonstrated in rats in vivo (~39-230 d), due to the use of a filament scaffold to enable coating and was likely exacerbated by metachromatic interactions caused by 1080. This work highlights that future development of the PPIs should primarily focus on removal of the filament scaffold, to afford implants with increased in vivo stability.

Laying low: Rugged lowland rainforest preferred by feral cats in the Australian Wet Tropics

Invasive mesopredators are responsible for the decline of many species of native mammals worldwide. Feral cats have been causally linked to multiple extinctions of Australian mammals since European colonization. While feral cats are found throughout Australia, most research has been undertaken in arid habitats, thus there is a limited understanding of feral cat distribution, abundance, and ecology in Australian tropical rainforests. We carried out camera-trapping surveys at 108 locations across seven study sites, spanning 200 km in the Australian Wet Tropics. Single-species occupancy analysis was implemented to investigate how environmental factors influence feral cat distribution. Feral cats were detected at a rate of 5.09 photographs/100 days, 11 times higher than previously recorded in the Australian Wet Tropics. The main environmental factors influencing feral cat occupancy were a positive association with terrain ruggedness, a negative association with elevation, and a higher affinity for rainforest than eucalypt forest. These findings were consistent with other studies on feral cat ecology but differed from similar surveys in Australia. Increasingly harsh and consistently wet weather conditions at higher elevations, and improved shelter in topographically complex habitats may drive cat preference for lowland rainforest. Feral cats were positively associated with roads, supporting the theory that roads facilitate access and colonization of feral cats within more remote parts of the rainforest. Higher elevation rainforests with no roads could act as refugia for native prey species within the critical weight range. Regular monitoring of existing roads should be implemented to monitor feral cats, and new linear infrastructure should be limited to prevent encroachment into these areas. This is pertinent as climate change modeling suggests that habitats at higher elevations will become similar to lower elevations, potentially making the environment more suitable for feral cat populations.

Raiders of the last ark: the impacts of feral cats on small mammals in Tasmanian forest ecosystems

Feral individuals of the cat Felis catus are recognized internationally as a threat to biodiversity. Open, non-insular systems support a large proportion of the world's biodiversity, but the population-level impacts of feral cats in these systems are rarely elucidated. This limits prioritization and assessment of the effectiveness of management interventions. We quantified the predatory impact of feral cats on small mammals in open, non-insular forest systems in Tasmania, Australia in the context of other factors hypothesized to affect small mammal densities and survival, namely the density of a native carnivore, co-occurring small mammals, and rainfall. Change in feral cat density was the most important determinant of small mammal density and survival. We calculated that, on average, a 50% reduction in feral cat density could result in 25% and 10% increases in the density of the swamp rat Rattus lutreolus and long-tailed mouse Pseudomys higginsi, respectively. Low-level culling of feral cats that we conducted on two of our four study sites to experimentally alter feral cat densities revealed that swamp rat survival was highest when feral cat densities were stable. We conclude that feral cats exert downward pressure on populations of indigenous small mammals in temperate forest systems. However, alleviating this downward pressure on prey by culling a large proportion of the feral cat population is difficult as current methods for reducing feral cat populations in cool temperate forest systems are ineffective, and potentially even counterproductive. We suggest using an adaptive approach that regularly and robustly monitors how feral cats and small mammals respond to management interventions that are intended to conserve vulnerable prey species.

Using 3D geometric morphometrics to aid taxonomic and ecological understanding of a recent speciation event within a small Australian marsupial (Antechinus: Dasyuridae)

Taxonomic distinction of species forms the foundation of biodiversity assessments and conservation priorities. However, traditional morphological and/or genetics-based taxonomic assessments frequently miss the opportunity of elaborating on the ecological and functional context of species diversification. Here, we used 3D geometric morphometrics of the cranium to improve taxonomic differentiation and add ecomorphological characterization of a young cryptic divergence within the carnivorous marsupial genus Antechinus. Specifically, we used 168 museum specimens to characterize the recently proposed clades A. stuartii ‘south’, A. stuartii ‘north’ and A. subtropicus. Beyond slight differences attributable to overall size (and, therefore, not necessarily diagnostic), we also found clear allometry-independent shape variation. This allowed us to define new, easily measured diagnostic traits in the palate, which differentiate the three clades. Contrary to previous suggestions, we found no support for a latitudinal gradient as causing the differentiation between the clades. However, skull shape co-varied with temperature and precipitation seasonality, suggesting that the clades may be adapted to environmental variables that are likely to be impacted by climate change. Our study demonstrates the use of 3D geometric morphometrics to improve taxonomic diagnosis of cryptic mammalian species, while providing perspectives on the adaptive origins and potential future threats of mammalian diversity.

Relaxed predation theory: size, sex and brains matter

Australia's wildlife is being considerably impacted by introduced mammalian predators such as cats (Felis catus), dogs (Canis lupus familiaris), and foxes (Vulpes vulpes). This is often attributed to native wildlife being naïve to these introduced predators. A systematic review of the literature reveals that native metatherians (body mass range 0.02-25 kg) do not recognise, and show relaxed antipredator behaviours towards, native and some introduced mammalian predators. Native eutherians (all with body mass < 2 kg), however, do appear to recognise and exhibit antipredator behaviours towards both native and introduced predators. Based on our findings, we propose a novel theory, the 'Relaxed Predation Theory'. Our new theory is based on the absence of large mammalian predators leading to reduced predation pressure in Australia during the past 40000-50000 years, and on three key differences between Australian metatherians and eutherians: size, sex, and brains. In light of this Relaxed Predation Theory, we make a number of recommendations for the conservation of Australian wildlife: (i) predator avoidance training of suitable species; (ii) exclusion fencing to exclude some, but not all, predators to facilitate the development of antipredator behaviours; (iii) captive breeding programs to prevent the extinction of some species; and (iv) reintroduction of Australia's larger predators, potentially to compete with and displace introduced predators. A more detailed understanding of the responses of Australian mammals to predators will hopefully contribute to the improved conservation of susceptible species.

Body Size and Bite Force of Stray and Feral Cats-Are Bigger or Older Cats Taking the Largest or More Difficult-to-Handle Prey?

As carnivorans rely heavily on their head and jaws for prey capture and handling, skull morphology and bite force can therefore reflect their ability to take larger or more difficult-to-handle prey. For 568 feral and stray cats (Felis catus), we recorded their demographics (sex and age), source location (feral or stray) and morphological measures (body mass, body condition); we estimated potential bite force from skull measurements for n = 268 of these cats, and quantified diet composition from stomach contents for n = 358. We compared skull measurements to estimate their bite force and determine how it varied with sex, age, body mass, body condition. Body mass had the strongest influence of bite force. In our sample, males were 36.2% heavier and had 20.0% greater estimated bite force (206.2 ± 44.7 Newtons, n = 168) than females (171.9 ± 29.3 Newtons, n = 120). However, cat age was the strongest predictor of the size of prey that they had taken, with older cats taking larger prey. The predictive power of this relationship was poor though (r² < 0.038, p < 0.003), because even small cats ate large prey and some of the largest cats ate small prey, such as invertebrates. Cats are opportunistic, generalist carnivores taking a broad range of prey. Their ability to handle larger prey increases as the cats grow, increasing their jaw strength, and improving their hunting skills, but even the smallest cats in our sample had tackled and consumed large and potentially 'dangerous' prey that would likely have put up a defence.

Living with the enemy: a threatened prey species coexisting with feral cats on a fox-free island

Abstract ContextFeral domestic cats (Felis catus) have contributed to substantial loss of Australian wildlife, particularly small- and medium-sized terrestrial mammals. However, mitigating cat impacts remains challenging. Understanding the factors that facilitate coexistence between native prey and their alien predators could aid better pest management and conservation actions. AimsWe estimated feral cat density, examined the impact of habitat cover on long-nosed potoroos (Potorous tridactylus tridactylus), and assessed the spatial and temporal interactions between cats and potoroos in the ‘Bluegums’ area of French Island, south-eastern Australia. Materials and methodsWe operated 31 camera stations across Bluegums for 99 consecutive nights in each of winter 2018 and summer 2018/19. We used a spatially explicit capture–recapture model to estimate cat density, and two-species single-season occupancy models to assess spatial co-occurrence of cats and potoroos. We assessed the influence of vegetation cover and cat activity on potoroo activity by using a dynamic occupancy model. We also used image timestamps to describe and compare the temporal activities of the two species. Key resultsBluegums had a density of 0.77 cats per km2 across both seasons, although this is a conservative estimate because of the presence of unidentified cats. Cats and long-nosed potoroos were detected at 94% and 77% of camera stations, respectively. Long-nosed potoroo detectability was higher in denser vegetation and this pattern was stronger at sites with high cat activity. Cats and potoroos overlapped in their temporal activity, but their peak activity times differed. Conclusions Feral cat density at Bluegums, French Island, is higher than has been reported for mainland Australian sites, but generally lower than in other islands. Long-nosed potoroos were positively associated with cats, potentially indicating cats tracking potoroos as prey or other prey species that co-occur with potoroos. Temporal activity of each species differed, and potoroos sought more complex habitat, highlighting possible mechanisms potoroos may use to reduce their predation risk when co-occurring with cats. ImplicationsOur study highlighted how predator and prey spatial and temporal interactions, and habitat cover and complexity (ecological refuges), may influence the ability for native prey to coexist with invasive predators. We encourage more consideration and investigation of these factors, with the aim of facilitating more native species to persist with invasive predators or be reintroduced outside of predator-free sanctuaries, exclosures and island safe havens.

Conserving Australia’s threatened native mammals in predator-invaded, fire-prone landscapes

Abstract Inappropriate fire regimes and predation by introduced species each pose a major threat to Australia’s native mammals. They also potentially interact, an issue that is likely to be contributing to the ongoing collapse of native mammal communities across Australia. In the present review, I first describe the mechanisms through which fire could create predation pinch points, exacerbating the impacts of predators, including red foxes, Vulpes vulpes, and feral cats, Felis catus, on their native mammalian prey. These mechanisms include a localised increase in predator activity (a numerically mediated pathway) and higher predator hunting success after fire (a functionally moderated pathway), which could both increase native mammal mortality and limit population recovery in fire-affected landscapes. Evidence for such interactions is growing, although largely based on unreplicated experiments. Improving native mammal resilience to fire in predator-invaded landscapes requires addressing two key questions: how can the impacts of introduced predators on native mammals in fire-affected areas be reduced; and, does a reduction in predation by introduced species result in higher native mammal survival and population recovery after fire? I then examine potential management options for reducing predator impacts post-fire. The most feasible are landscape-scale predator control and the manipulation of fire regimes to create patchy fire scars. However, robust field experiments with adequate statistical power are required to assess the effectiveness of these approaches and preclude null (e.g. compensatory mortality) or adverse (e.g. mesopredator or competitor release) outcomes. Ongoing predator management and prescribed burning programs provide an opportunity to learn through replicated natural experiments as well as experimental manipulations. Standardised reporting protocols and cross-jurisdiction monitoring programs would help achieve necessary spatial and environmental replication, while multi-trophic, spatially explicit simulation models could help synthesise findings from disparate study designs, predict management outcomes and generate new hypotheses. Such approaches will be key to improving management of the complex mechanisms that drive threatened native mammal populations in Australia’s predator-invaded, fire-prone landscapes.

We need to worry about Bella and Charlie: the impacts of pet cats on Australian wildlife

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.

Distribution and diet of feral cats (Felis catus) in the Wet Tropics of north-eastern Australia, with a focus on the upland rainforest

Abstract ContextFeral cats have been identified as a key threat to Australia’s biodiversity, particularly in arid areas and tropical woodlands. Their presence, abundance and potential impacts in rainforest have received less attention. AimsTo investigate the distribution and diet of feral cats (Felis catus) in upland rainforest of the Wet Tropics. MethodsWe collated available occurrence records from the Wet Tropics, and data from upland camera-trapping surveys over an 8-year period, to assess geographic and elevational distribution of feral cats in the bioregion. We also assessed the diet of feral cats from scats collected at upland sites. Key resultsFeral cats are widespread through the Wet Tropics bioregion, from the lowlands to the peaks of the highest mountains (&gt;1600m), and in all vegetation types. Abundance appears to vary greatly across the region. Cats were readily detected during camera-trap surveys in some upland rainforest areas (particularly in the southern Atherton Tablelands and Bellenden Ker Range), but were never recorded in some areas (Thornton Peak, the upland rainforest of Windsor Tableland and Danbulla National Park) despite numerous repeated camera-trap surveys over the past 8 years at some of these sites. Scat analysis suggested that small mammals comprise ~70% of the diet of feral cats at an upland rainforest site. Multivariate analysis could not detect a difference in mammal community at sites where cats were detected or not. ConclusionsFeral cats are widespread in the Wet Tropics and appear to be common in some upland areas. However, their presence and abundance are variable across the region, and the drivers of this variability are not resolved. Small mammals appear to be the primary prey in the rainforest, although the impacts of cats on the endemic and threatened fauna of the Wet Tropics is unknown. ImplicationsGiven their documented impact in some ecosystems, research is required to examine the potential impact of cats on Wet Tropics fauna, particularly the many upland endemic vertebrates. Studies are needed on (1) habitat and prey selection, (2) population dynamics, and (3) landscape source–sink dynamics of feral cats in the Wet Tropics.

Long-term benefits and short-term costs: small vertebrate responses to predator exclusion and native mammal reintroductions in south-western New South Wales, Australia

Abstract ContextThe success of conservation fences at protecting reintroduced populations of threatened mammals from introduced predators has prompted an increase in the number and extent of fenced exclosures. Excluding introduced species from within conservation fences could also benefit components of insitu faunal assemblages that are prey for introduced predators, such as reptiles and small mammals. Conversely, reintroduced mammals may compete with smaller mammals and reptiles for resources, or even prey on them. AimsIn a 10-year study from 2008, we examine how small terrestrial vertebrates respond to the exclusion of introduced predators, the feral cat (Felis catus) and red fox (Vulpes Vulpes), introduced herbivores and the reintroduction of regionally extinct mammal species. MethodsDifferences in the yearly relative abundance of reptiles and mammals according to habitat type and whether sites were fenced or not, were tested using multivariate generalised linear models. Next, we calculated univariate P-values to identify individual species that showed significant relationships, positive and negative, with any of the explanatory variables. Key resultsTotal captures of reptiles were lower inside the conservation fence in all years, whereas total captures of small mammals were markedly higher inside the fenced area, notably in dasyurids. ConclusionOur results showed that conservation fences can deliver benefits for some fauna (but not all) beyond facilitating the reintroduction of highly threatened mammals. ImplicationsOur results demonstrated the consequential impacts of introduced predators on the Australian small mammal fauna, and showed that predator-exclusion fences can be an effective conservation intervention for this guild.

Predation by introduced cats Felis catus on Australian frogs: compilation of species records and estimation of numbers killed

Abstract ContextWe recently estimated the numbers of reptiles, birds and mammals killed by cats (Felis catus) in Australia, with these assessments providing further evidence that cats have significant impacts on Australian wildlife. No previous studies have estimated the numbers of frogs killed by cats in Australia and there is limited comparable information from elsewhere in the world. AimsWe sought to (1) estimate the numbers of frogs killed by cats in Australia and (2) compile a list of Australian frog species known to be killed by cats. MethodsFor feral cats, we estimated the number of frogs killed from information on their frequency of occurrence in 53 cat dietary studies (that examined stomach contents), the mean number of frogs in dietary samples that contained frogs, and the numbers of cats in Australia. We collated comparable information for take of frogs by pet cats, but the information base was far sparser. Key resultsFrogs were far more likely to be reported in studies that sampled cat stomachs than cat scats. The mean frequency of occurrence of frogs in cat stomachs was 1.5%. The estimated annual per capita consumption by feral cats in Australia’s natural environments is 44 frogs, and, hence, the annual total take is estimated at 92 million frogs. The estimated annual per capita consumption by pet cats is 0.26 frogs, for a total annual kill of one million frogs by pet cats. Thirty native frog species (13% of the Australian frog fauna) are known to be killed by cats: this tally does not include any of the 51 threatened frog species, but this may simply be because no cat dietary studies have occurred within the small ranges typical of threatened frog species. ConclusionsThe present study indicated that cats in Australia kill nearly 100 million frogs annually, but further research is required to understand the conservation significance of such predation rates. ImplicationsThe present study completed a set of reviews of the impacts of cats on Australian terrestrial vertebrates. Cat predation on Australian frogs is substantial, but is likely to be markedly less than that on Australian reptiles, birds and mammals.

Going to ground: implications of ground use for the conservation of an arboreal marsupial

On the basis of previous observations, the critically endangered western ringtail possum (Pseudocheirus occidentalis) has been described as strictly arboreal. Using motion-sensing cameras placed in bushland remnants and residential gardens, we demonstrate that the species uses the ground during its nocturnally active period. To acknowledge that ground use may make the species more susceptible to terrestrial predators than previously thought, we propose that the species should not be described as ‘strictly’ arboreal.

Assessing Risks to Wildlife from Free-Roaming Hybrid Cats: The Proposed Introduction of Pet Savannah Cats to Australia as a Case Study

Simple Summary

The domestic cat, Felis catus, is often cross-bred with other species in the cat family to produce hybrid or ‘designer’ cats that are sought by people as pets. However, hybrid cats are often surrendered to wildlife shelters, or released, which leads to concern that they may establish free-roaming populations and damage native wildlife. In 2008, the Australian government rejected an application, on precautionary grounds, to import savannah cats (hybrids of the domestic cat and serval Leptailurus serval) into the country. We review the limited information informing this decision and then present a framework that identifies the native mammal species likely to have been most at risk of predation from savannah cats if importation and establishment had occurred. Assuming that savannah cats hunt similar prey to those that are hunted by both parent species, we estimate that 91% of Australia’s extant terrestrial mammal fauna would likely face some risk of predation from savannah cats, including 93% of non-volant mammal species that have threatened conservation status. The framework results strongly validate the decision to ban savannah cats from Australia. We suggest that our framework approach could be adapted to assess the likely risks that are posed by the arrival of other hybrid cats or hybrids of other animals.

Abstract

Hybrid cats—created by crossing different species within the family Felidae—are popular pets, but they could potentially threaten native species if they escape and establish free-roaming populations. To forestall this possibility, the Australian government imposed a specific ban on importation of the savannah cat, a hybrid created by crossing the domestic cat Felis catus and serval Leptailurus serval, in 2008. We develop a decision–framework that identifies those species of non-volant native mammals in Australia that would likely have been susceptible to predation by savannah cats if importation and establishment had occurred. We assumed that savannah cats would hunt ecologically similar prey to those that are depredated by both the domestic cat and the serval, and categorised native mammals as having different levels of susceptibility to predation by savannah cats based on their size, habitat range, and behaviour. Using this framework, we assessed savannah cats as likely to add at least 28 extant native mammal species to the 168 that are known already to be susceptible to predation by the domestic cat, posing a risk to 91% of Australia’s extant non-volant terrestrial mammal species (n = 216) and to 93% of threatened mammal species. The framework could be generalised to assess risks from any other hybrid taxa.

Cat Gets Its Tern: A Case Study of Predation on a Threatened Coastal Seabird

Domestic cats have a cosmopolitan distribution, commonly residing in urban, suburban and peri-urban environments that are also critical for biodiversity conservation. This study describes the impact of a desexed, free-roaming cat on the behavior of a threatened coastal seabird, the Australian Fairy Tern, Sternula nereis nereis, in Mandurah, south-western Australia. Wildlife cameras and direct observations of cat incursions into the tern colony at night, decapitated carcasses of adult terns, dead, injured or missing tern chicks, and cat tracks and scats around the colony provided strong evidence of cat predation, which led to an initial change in nesting behavior and, ultimately, colony abandonment and the reproductive failure of 111 nests. The death of six breeding terns from the population was a considerable loss for this threatened species and had the potential to limit population growth. This study highlights the significant negative impacts of free-roaming cats on wildlife and the need for monitoring and controlling cats at sites managed for species conservation. It also provides strong evidence against the practice of trap-neuter-release programs and demonstrates that desexed cats can continue to negatively impact wildlife post-release directly through predation, but also indirectly through fundamental changes in prey behavior and a reduction in parental care.

Habitat and introduced predators influence the occupancy of small threatened macropods in subtropical Australia

Australia has had the highest rate of mammal extinctions in the past two centuries when compared to other continents. Frequently cited threats include habitat loss and fragmentation, changed fire regimes and the impact of introduced predators, namely the red fox (Vulpes vulpes) and the feral cat (Felis catus). Recent studies suggest that Australia's top predator, the dingo (Canis dingo), may have a suppressive effect on fox populations but not on cat populations. The landscape of fear hypothesis proposes that habitat used by prey species comprises high to low risk patches for foraging as determined by the presence and ubiquity of predators within the ecosystem. This results in a landscape of risky versus safe areas for prey species. We investigated the influence of habitat and its interaction with predatory mammals on the occupancy of medium-sized mammals with a focus on threatened macropodid marsupials (the long-nosed potoroo [Potorous tridactylous] and red-legged pademelon [Thylogale stigmatica]). We assumed that differential use of habitats would reflect trade-offs between food and safety. We predicted that medium-sized mammals would prefer habitats for foraging that reduce the risk of predation but that predators would have a positive relationship with medium-sized mammals. We variously used data from 298 camera trap sites across nine conservation reserves in subtropical Australia. Both dingoes and feral cats were broadly distributed, whilst the red fox was rare. Long-nosed potoroos had a strong positive association with dense ground cover, consistent with using habitat complexity to escape predation. Red-legged pademelons showed a preference for open ground cover, consistent with a reliance on rapid bounding to escape predation. Dingoes preferred areas of open ground cover whereas feral cats showed no specific habitat preference. Dingoes were positively associated with long-nosed potoroos whilst feral cats were positively associated with red-legged pademelons. Our study highlights the importance of habitat structure to these threatened mammals and also the need for more detailed study of their interactions with their predators.

Phylogeography of southern brown and golden bandicoots: implications for the taxonomy and distribution of endangered subspecies and species

Southern brown (Isoodon obesulus) and golden (Isoodon auratus) bandicoots are iconic Australian marsupials that have experienced dramatic declines since European settlement. Conservation management programs seek to protect the remaining populations; however, these programs are impeded by major taxonomic uncertainties. We investigated the history of population connectivity to inform subspecies and species boundaries through a broad-scale phylogeographic and population genetic analysis of Isoodon taxa. Our analyses reveal a major east–west phylogeographic split within I. obesulus/I. auratus, supported by both mtDNA and nuclear gene analyses, which is not coincident with the current species or subspecies taxonomy. In the eastern lineage, all Tasmanian samples formed a distinct monophyletic haplotype group to the exclusion of all mainland samples, indicative of long-term isolation of this population from mainland Australia and providing support for retention of the subspecific status of the Tasmanian population (I. o. affinis). Analyses further suggest that I. o. obesulus is limited to south-eastern mainland Australia, representing a significant reduction in known range. However, the analyses provide no clear consensus on the taxonomic status of bandicoot populations within the western lineage, with further analyses required, ideally incorporating data from historical museum specimens to fill distributional gaps.