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.     

Feral Cats Are Better Killers in Open Habitats,Revealed by Animal-Borne Video

One of the key gaps in understanding the impacts of predation by small mammalian predators on prey is how habitat structure affects the hunting success of small predators, such as feral cats. These effects are poorly understood due to the difficulty of observing actual hunting behaviours. We attached collar-mounted video cameras to feral cats living in a tropical savanna environment in northern Australia, and measured variation in hunting success among different microhabitats (open areas, dense grass and complex rocks). From 89 hours of footage, we recorded 101 hunting events, of which 32 were successful. Of these kills, 28% were not eaten. Hunting success was highly dependent on microhabitat structure surrounding prey, increasing from 17% in habitats with dense grass or complex rocks to 70% in open areas. This research shows that habitat structure has a profound influence on the impacts of small predators on their prey. This has broad implications for management of vegetation and disturbance processes (like fire and grazing) in areas where feral cats threaten native fauna. Maintaining complex vegetation cover can reduce predation rates of small prey species from feral cat predation.     

Do dingoes suppress the activity of feral cats in northern Australia?

Large predators can have profound impacts on community composition. Not only do they directly affect prey abundance, they also indirectly affect prey abundance through their direct effects on smaller predators. In Australia, dingoes fill the role of a large predator and, in southern Australia, have clear impacts on introduced foxes. Their effect on introduced cats, however, is less clear. Here we present data from multiple sites across northern Australia (where foxes are absent), which reveal a negative correlation between cat and dingo activity. This relationship could arise because cats avoid areas where dingoes are active, or because cats are less abundant in areas with high dingo densities, or a combination of both. At a subset of our study sites, we experimentally reduced dingo (but not cat) abundance by poison baiting. This resulted in a 55% drop in dingo activity within 4 weeks of baiting, but without a compensatory increase in cat activity. This suggests the negative correlation between cat and dingo activity is not a simple consequence of cats reactively avoiding areas with higher dingo traffic, but rather, that there are fewer cats in areas where dingoes are more active. This study is a rare demonstration of the potential for dingoes to affect the behaviour and potentially the population size of feral cats, and therefore reduce the impact of feral cats on vulnerable native prey species.     

A global review of the impacts of invasive cats on island endangered vertebrates

Cats are generalist predators that have been widely introduced to the world's ~179 000 islands. Once introduced to islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators and can suffer severe population declines and even extinction. As islands house a disproportionate share of terrestrial biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threatened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on different native species in different types of island ecosystems can increase the efficiency of this conservation tool. We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported from at least 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds, and 27 mammals), many of which are listed by the International Union for the Conservation of Nature. A meta‐analysis suggests that cat impacts were greatest on endemic species, particularly mammals and greater when non‐native prey species were also introduced. Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles.     

Effects of feral cats on the evolution of anti-predator behaviours in island reptiles: insights from an ancient introduction

Exotic predators have driven the extinction of many island species. We examined impacts of feral cats on the abundance and anti-predator behaviours of Aegean wall lizards in the Cyclades (Greece), where cats were introduced thousands of years ago. We compared populations with high and low cat density on Naxos Island and populations on surrounding islets with no cats. Cats reduced wall lizard populations by half. Lizards facing greater risk from cats stayed closer to refuges, were more likely to shed their tails in a standardized assay, and fled at greater distances when approached by either a person in the field or a mounted cat decoy in the laboratory. All populations showed phenotypic plasticity in flight initiation distance, suggesting that this feature is ancient and could have helped wall lizards survive the initial introduction of cats to the region. Lizards from islets sought shelter less frequently and often initially approached the cat decoy. These differences reflect changes since islet isolation and could render islet lizards strongly susceptible to cat predation.     

Diet of the feral cat,Felis catus,in central Australian grassland habitats: do cat attributes influence what they eat?

The house cat Felis catus was introduced to Australia as a pet and means of rodent control over 200 years ago, but now has established feral populations and has become a serious threat to native wildlife. Using stomach content analysis of 73 feral cats from semi-arid grassland habitats in Queensland, Australia, we aimed to identify dominant prey groups in the cats' diet and to explore associations between the diversity of prey eaten and attributes of the cats including body size, condition, sex, age and coat colour. We also sought to determine any relationships between cat size and the size of the dominant prey in the diet, the long-haired rat Rattus villosissimus. Mammals and reptiles were the dominant prey, with R. villosissimus occurring in 60 % of samples and comprising more than half of all prey by volume. Birds and terrestrial invertebrates were the next most important contributors to the diet, but fish, frogs and freshwater crustaceans also were surprisingly well represented. The dietary diversity of cats was largely unrelated to any of the cat attributes that we measured, although a positive relationship emerged between cat head width and the range of prey types eaten. Our study was conducted during a population irruption of R. villosissimus and confirms that cats are able to exploit an abundant focal prey resource when the opportunity occurs. Further research now is needed to explore associations between diet and cat attributes during periods when rats are scarce.     

Abundance and detection of feral cats decreases after severe fire on Kangaroo Island,Australia

Predation by feral cats (Felis catus) has caused the extinction of many native species in Australia and globally. There is growing evidence that the impacts of feral cats can be amplified in post-fire environments, as cats are drawn to hunt in or around recently burnt areas and are also more effective hunters in open habitats. In 2018–2019, we established arrays of camera traps to estimate the abundance of feral cats on Kangaroo Island, South Australia. Much of the island (including five of our seven survey sites) was subsequently burnt in a severe wildfire (December 2019–February 2020). We re-sampled the sites 3–8 months post-fire (seven sites) and 11–12 months post-fire (three sites). At two unburnt sites sampled post-fire, it was possible to produce density estimates of cats using a spatially explicit capture–recapture approach. Where estimating density was not possible (due to low detections or individual cats not being distinguishable), the number of individuals and percentage of trap nights with detections was compared between the sampling periods. Some low-level cat control occurred within 2 km of three of the seven arrays (all within the burn scar) within 3 months of the fire. Across the five burnt sites, there was a decline in cat detections post-fire (including those without post-fire cat control). At 3–8 months post-fire, there was, on average, a 57% reduction in the number of individual cats, and a 65% reduction in the number of nights with cat detections, relative to pre-fire levels. Although cat detections declined following the fire, reduced population sizes of prey species and reduced cover as a result of the fire might still mean that cat predation is a threat to some surviving prey species. Management that reduces feral cat predation pressure on wildlife following wildfire should enhance the likelihood of post-fire wildlife persistence and recovery.     

Introduced cats Felis catus eating a continental fauna: inventory and traits of Australian mammal species killed

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Diets of sympatric native and introduced carnivores in the Barrington Tops,eastern Australia

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.     

Know thy enemy: Behavioural response of a native mammal (Rattus lutreolus velutinus) to predators of different coexistence histories

Abstract Predation is recognized as a major selective pressure influencing population dynamics and evolutionary processes. Prey species have developed a variety of predator avoidance strategies, not least of which is olfactory recognition. However, within Australia, European settlement has brought with it a number of introduced predators, perhaps most notably the red fox (Vulpes vulpes) and domestic cat (Felis catus), which native prey species may be unable to recognize and thus avoid due to a lack of coexistence history. This study examined the response of native Tasmanian swamp rats (Rattus lutreolus velutinus) to predators of different coexistence history (native predator‐ spotted‐tail quoll (Dasyurus maculatus), domestic cats and the recently introduced red fox). We used an aggregate behavioural response of R. l. velutinus to predator integumental odour in order to assess an overall behavioural response to predation risk. Rattus lutreolus velutinus recognized the integumental odour of the native quoll (compared with control odours) but did not respond to either cat or fox scent (compared with control odur). In contrast, analyses of singular behaviours resulted in the conclusion that rats did not respond differentially to either native or introduced predators, as other studies have concluded. Therefore, measuring risk assessment behaviours at the level of overall aggregate response may be more beneficial in understanding and analysing complex behavioural patterns such as predator detection and recognition. These results suggest that fox and cat introductions (and their interactive effects) may have detrimental impacts upon small native Tasmanian mammals due to lack of recognition and thus appropriate responses.     

Trophic ecology of an introduced top predator (Felis catus) on a small African oceanic islet (Santa Luzia,Cabo Verde Islands)

Studies on feral cat diet offer important ecological information and are the first step towards determining their impact upon endangered species. However, in comparing seasonal changes in diet with seasonal prey availability, the scarce amount of research into oceanic islands worldwide must be considered when deciding if a specific population is actually affected by cat predation. Cat diet was analysed on Santa Luzia (Cabo Verde Islands) since this invasive predator is considered one of the main threats to native endangered species that require conservation measures. These previous studies were carried out in different seasons, providing contrasting results, skinks being more preyed upon in the rainy season and mice in the driest periods. To check these different results, we focussed on how cat diet varied seasonally in response to changes in prey abundance. Saurians were the most important prey group, followed by mice, invertebrates and birds. No seasonal differences were, however, observed in the different prey groups consumed, saurians being the main prey in both seasons. All cases reflected their respective abundances. Results corroborate the generalist and opportunistic trophic ecology of feral cats, providing important information to assess their impact on prey populations and design future eradication programmes.     

Impacts and management of feral cats Felis catus in Australia

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Opinions from the front lines of cat colony management conflict

Outdoor cats represent a global threat to terrestrial vertebrate conservation, but management has been rife with conflict due to differences in views of the problem and appropriate responses to it. To evaluate these differences we conducted a survey of opinions about outdoor cats and their management with two contrasting stakeholder groups, cat colony caretakers (CCCs) and bird conservation professionals (BCPs) across the United States. Group opinions were polarized, for both normative statements (CCCs supported treating feral cats as protected wildlife and using trap neuter and release [TNR] and BCPs supported treating feral cats as pests and using euthanasia) and empirical statements. Opinions also were related to gender, age, and education, with females and older respondents being less likely than their counterparts to support treating feral cats as pests, and females being less likely than males to support euthanasia. Most CCCs held false beliefs about the impacts of feral cats on wildlife and the impacts of TNR (e.g., 9% believed feral cats harmed bird populations, 70% believed TNR eliminates cat colonies, and 18% disagreed with the statement that feral cats filled the role of native predators). Only 6% of CCCs believed feral cats carried diseases. To the extent the beliefs held by CCCs are rooted in lack of knowledge and mistrust, rather than denial of directly observable phenomenon, the conservation community can manage these conflicts more productively by bringing CCCs into the process of defining data collection methods, defining study/management locations, and identifying common goals related to caring for animals.     

Existing and emerging high impact invasive species are characterized by higher functional responses than natives

Predicting ecological impacts of invasive species and identifying potentially damaging future invaders are research priorities. Since damage by invaders is characterized by their depletion of resources, comparisons of the ‘functional response’ (FR; resource uptake rate as a function of resource density) of invaders and natives might predict invader impact. We tested this by comparing FRs of the ecologically damaging ‘world''s worst’ invasive fish, the largemouth bass (Micropterus salmoides), with a native equivalent, the Cape kurper (Sandelia capensis), and an emerging invader, the sharptooth catfish (Clarias gariepinus), with the native river goby (Glossogobius callidus), in South Africa, a global invasion hotspot. Using tadpoles (Hyperolius marmoratus) as prey, we found that the invaders consumed significantly more than natives. Attack rates at low prey densities within invader/native comparisons reflected similarities in predatory strategies; however, both invasive species displayed significantly higher Type II FRs than the native comparators. This was driven by significantly lower prey handling times by invaders, resulting in significantly higher maximum feeding rates. The higher FRs of these invaders are thus congruent with, and can predict, their impacts on native communities. Comparative FRs may be a rapid and reliable method for predicting ecological impacts of emerging and future invasive species.     

Patterns of Detection and Capture Are Associated with Cohabiting Predators and Prey

Avoidance behaviour can play an important role in structuring ecosystems but can be difficult to uncover and quantify. Remote cameras have great but as yet unrealized potential to uncover patterns arising from predatory, competitive or other interactions that structure animal communities by detecting species that are active at the same sites and recording their behaviours and times of activity. Here, we use multi-season, two-species occupancy models to test for evidence of interactions between introduced (feral cat Felis catus) and native predator (Tasmanian devil Sarcophilus harrisii) and predator and small mammal (swamp rat Rattus lutreolus velutinus) combinations at baited camera sites in the cool temperate forests of southern Tasmania. In addition, we investigate the capture rates of swamp rats in traps scented with feral cat and devil faecal odours. We observed that one species could reduce the probability of detecting another at a camera site. In particular, feral cats were detected less frequently at camera sites occupied by devils, whereas patterns of swamp rat detection associated with devils or feral cats varied with study site. Captures of swamp rats were not associated with odours on traps, although fewer captures tended to occur in traps scented with the faecal odour of feral cats. The observation that a native carnivorous marsupial, the Tasmanian devil, can suppress the detectability of an introduced eutherian predator, the feral cat, is consistent with a dominant predator – mesopredator relationship. Such a relationship has important implications for the interaction between feral cats and the lower trophic guilds that form their prey, especially if cat activity increases in places where devil populations are declining. More generally, population estimates derived from devices such as remote cameras need to acknowledge the potential for one species to change the detectability of another, and incorporate this in assessments of numbers and survival.     

Filling the Ark: Animal Welfare in Disasters

ABSTRACT

Populations of feral domestic cats and free-roaming, owned cats have increased throughout the United States, affecting wildlife and public health and warranting attention from a variety of management agencies. The contentious issue of feral cat management requires a greater understanding of public attitudes towards cats and preferences. We used an anonymous internet survey of randomly selected Athens-Clarke County, Georgia households to identify general public perceptions of domestic cats and preferences for cat management. We examined factors that may influence attitudes towards cats, and management including: knowledge about cats, experiences with cats and demographic variables. Results indicate that more residents have positive experiences with feral cats than negative, cat owners have greater knowledge of cats than non-cat owners, and animal welfare or conservation organization membership has a significant effect on attitudes towards cats. A majority of survey respondents agreed that more effective feral cat management is needed yet did not approve of trap-neuter-release (TNR) legislation recently passed in Athens-Clarke County. Logistic regression revealed that residents' attitudes were found to be more important than experiences or knowledge in supporting cat management legislation. Cat sanctuaries were found to be the most acceptable option to reduce feral cat populations (56%), followed by TNR (49%) and capturing and euthanizing cats (44%).     

Status of mammals on Groote Eylandt: Safe haven or slow burn?

Native mammals across northern Australia have suffered severe decline, with feral cats (Felis catus), introduced herbivores and changed fire regimes being implicated as drivers. However, uncertainty surrounding the relative contribution of each of these threats, and the interactions between them, is limiting the development of effective management strategies. The absence of introduced herbivores and cane toads (Rhinella marina) on Groote Eylandt, Northern Territory, provides an opportunity to evaluate some hypothesised threats in isolation of others. We used camera traps to investigate the correlates of native mammal distribution and abundance at 112 lowland savanna sites across Groote Eylandt. Two large grids of camera traps were also deployed to obtain estimates of feral cat density. We hypothesised that native mammal populations would be negatively associated with feral cat occupancy as well as frequent, large fires. Native mammal site‐occupancy on Groote Eylandt was generally higher compared to mainland Northern Territory. Feral cats were infrequently detected, precluding both an estimate of feral cat density and an evaluation of the relationship between feral cats and native mammals. We found no evidence that native mammal site‐occupancy or relative abundance is negatively associated with frequent, large fires. The relatively healthy state of native mammal populations on Groote Eylandt is likely due to the low density of feral cats, the benign fire regime and the absence of large introduced herbivores and cane toads. However, due to a lack of historical data, the current state of mammals should not be taken as evidence that these populations are safe from decline. This study highlights that the apparent resilience of mammal populations is a result of complex interactions between factors that vary substantially across the landscape. Caution is therefore required when making broad inferences about the drivers of mammal decline from studies that are spatially and temporally limited.     

Predicting bait uptake by feral cats,Felis catus,in semi‐arid environments

Feral cat control using aerial broadcasting of toxic baits continues to be used in the rangelands of Western Australia. The effectiveness of these operations has sometimes been compromised by different environmental factors that affect prey and cat numbers. This study demonstrates that the ratio of cats to their preferred prey (small mammals) can be used to predict the most effective time to bait. The regular baiting of three conservation sites offered an opportunity to study the relationship between feral cat abundance, the abundance of their prey and ingestion of toxic baits. Peron Peninsula on the mid‐west coast, Lorna Glen station in the northern Goldfields and the central Gibson Desert of Western Australia are sites where cat control using toxic baits has been routinely applied over the last 15 years. We postulated that bait ingestion by cats was linked to the availability of live prey. Small mammal abundance (capture rates in pit‐fall traps) and relative cat abundance (based on daily track counts) were assessed at these sites and the data used to produce a predator‐prey ratio index (PPRI). We used generalised linear mixed models to test the effect of prey abundance, prebaiting cat abundance and PPRI on baiting efficacy (BE). The best model for predicting efficacy of baiting contained only PPRI. This simple model was able to predict baiting success over the entire range of outcomes, from highly successful ( >75% cat reduction) to unsuccessful (0% cat reduction). The ability to predict feral cat BE in advance of planned toxic baiting operations will provide a valuable tool for wildlife managers involved in cat control.     

Rapid recovery of mammal fauna in the central Kimberley,northern Australia,following the removal of introduced herbivores

Australia has lost more native mammal species than any other country in the past two centuries, and this record of loss looks likely to worsen over the next few decades. Small‐ to medium‐sized mammals are declining in both distribution and density across large tracts of northern Australia's tropical savannas, including within protected areas. The most likely causes are a combination of changed fire patterns, the impacts of introduced herbivores and predation by feral cats. Here, in contrast to the prevailing trend across northern Australia, we report the recovery of native mammals in response to a large‐scale (>40 000 ha) destocking experiment carried out at Mornington Wildlife Sanctuary in the central Kimberley, north‐west Australia. Following the removal of introduced herbivores from 2004, the species richness and abundance of small native rodents and dasyurids increased significantly across all sampled habitats over the next 3 years. We discuss the implications of these results for guiding land management and applied research to help to reduce the impending risk of mammalian extinctions in northern Australia.     

Sign left by introduced and native predators feeding on Hutton's shearwaters Puffinus huttoni

Abstract

The identification of introduced and native predators is important for many conservation studies within New Zealand. Carcasses of Hutton's shearwaters were collected over three field seasons, and where predation was probable, the bodies were autopsied. Paired bites identified stoats as the principal predator of Hutton's shearwater, but also revealed that a feral cat was present within the colony. Stoats killed their prey with a bite to the back of the neck or head, and commenced feeding on the neck or head. Despite the limited number of cat‐killed birds, cats appeared to feed on Hutton's shearwaters differently from stoats, starting on the breast muscles. Harriers and kea left sign that allowed birds killed or scavenged by these native birds to be distinguished from those killed by stoats or cats.