Feral cat home-range size varies predictably with landscape productivity and population density

Spatial ecology to strengthen invasive snake management on islands

Knowledge on the spatial ecology of invasive predators positively contributes to optimizing their management, especially when involving cryptic and secretive species, such as snakes. However, this information is lacking for most invasive snakes, particularly on islands, where they are known to cause severe ecological and socio-economic impacts. This research is focused on assessing the spatial ecology of the California kingsnake (Lampropeltis californiae) on Gran Canaria to strengthen management actions. We monitored 15 radio-tagged individuals once per day on 9-11 days per month from July 2020 to June 2021 to calculate the species' home range and describe annual activity patterns in the invaded range. To account for the species' diel activity during the emergence period, we additionally monitored snakes from January to May 2021 during three consecutive days per month in four different time intervals each day. We detected movement (consecutive detections at least 6 m apart) in 31.68% of the 1146 detections during the whole monitoring period. Movements most frequently detected were shorter than 100 m (82.24%), and among them the range 0-20 m was the most recurrent (27.03%). The mean distance of movement was 62.57 ± 62.62 m in 1-2 days. Average home range was 4.27 ± 5.35 ha-calculated with the Autocorrelated Kernel Density Estimator (AKDE) at 95%-and did not significantly vary with SVL nor sex. We detected an extremely low value of motion variance (0.76 ± 2.62 σ²m) compared to other studies, with a general inactivity period from November to February, January being the less active month of the year. Diel activity was higher during central and evening hours than during early morning and night. Our results should be useful to improve control programs for this invasive snake (e.g., trap placement and visual survey guidance) on Gran Canaria. Our research highlights the importance of gathering spatial information on invasive snakes to enhance control actions, which can contribute to the management of secretive invasive snakes worldwide.

Application of genetic and Spatially Explicit Capture-Recapture analyses to design adaptive feral cat control in a large inhabited island

Faunas of oceanic islands have a high proportion of endemic species which contribute to the uniqueness of island communities. Island species are particularly naïve and vulnerable to alien predators, such as cats (Felis catus). On large, inhabited islands, where the complete eradication of feral cat populations is not considered feasible, control represents the best management option to lower their detrimental effects on native fauna. The first objective of our study was to investigate population genetics of feral cats of Réunion Island. The second objective was to understand the space use of feral cats established near the breeding colonies of the two endemic and endangered seabirds of Réunion Island, the Barau’s Petrel (Pterodroma baraui) and the Mascarene Petrel (Pseudobulweria aterrima). We evaluated genetic diversity, population structure and gene flow amongst six groups of feral cats located at a maximum of 10 km from known petrel colonies. We also analysed the behaviour and space use of one of these feral cat groups using camera-trap data and Spatially Explicit Capture-Recapture (SECR) models. Genetic analyses revealed that feral cats were structured in three genetic clusters explained mostly by the island topography. Two clusters were observed at five sampled sites, suggesting high connectivity amongst these sites. The last cluster was found in only one site, suggesting high isolation. This site was a remote mountain area located in the vicinity of one of the main Barau’s Petrel colonies. The behavioural study was conducted on this isolated feral cat population. Mark recapture analysis suggested that feral cats were present at low density and had large home ranges, which is probably explained by reduced food availability. Finally, we make several recommendations for refining feral cat management programmes on inhabited islands.

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.

Home Range and Activity Patterns of Free-Ranging Cats: A Case Study from a Chinese University Campus

Simple Summary

In this study, we used collar-mounted sensors to determine the home range size of free-ranging cats on a Chinese university campus. Twenty-nine adult cats (fifteen males and fourteen females) were tracked via attached GPS units from October 2018 to June 2020. Throughout the study, home range sizes ranged from 0.56 to 19.83 ha at 95% KDE for all cats. The home range of free-ranging cats is affected by the breeding status and sex; for example, male cats tend to have a larger home range size in the breeding season than in the non-breeding season, and in the breeding season, male cats generally have a larger home range than females. In the study of activity patterns, we provided the activity steps of free-ranging cats at different times of the day, and the mean (±SE) number of steps a cat takes per day was 19,863.96 ± 1627.21. The results show that free-ranging cats have more intense activities at twilight and relatively lower activity intensity in the afternoon. Our study provided a case study of the home range and activity patterns of free-ranging cats living on a Chinese university campus, and provided theoretical support for the management and conservation implications of free-ranging cats in cities.

Abstract

Human activities and the available resources influence the home range and activity patterns of free-ranging cats. Our objective in this study was to determine sex and breeding season vs. non-breeding season home range size, as well as activity patterns for unowned free-ranging cats at a university campus in China. Twenty-nine adult cats (fifteen males and fourteen females) were tracked with attached GPS units from October 2018 to June 2020. We considered the effects of sex and breeding status on the home range size of free-ranging cats. Male cats had larger home ranges (95% KDE: 12.60 ± 2.61 ha) than female cats (95% KDE: 5.02 ± 1.34 ha) in the breeding season. There was a seasonal effect on the home range size of male cats; for example, during the non-breeding season, the home range (95% KDE: 6.68 ± 1.22 ha) was smaller than that during the breeding season (95% KDE: 12.60 ± 2.61 ha), while female cats tended to have larger home ranges in the non-breeding season (95% KDE: 7.73 ± 2.77 ha) than in the breeding season (95% KDE: 5.02 ± 1.34 ha). We used the number of activity steps to measure the activity intensity of cats to explore their activity patterns. The mean (±SE) number of steps a cat takes per day was 19,863.96 ± 1627.21. There were two peak periods of activity in a day, 6:00–10:00 and 17:00–21:00. Our study provided a case study of the home range and activity patterns of free-ranging cats living on a Chinese university campus, and the results show that the home range of free-ranging cats is affected by the breeding status and sex, and free-ranging cats have more intense activities at twilight and relatively lower activity intensity in the afternoon. The results provided theoretical support for the management and conservation implications of free-ranging cats in cities.

Mapping the "catscape" formed by a population of pet cats with outdoor access

The domestic cat (Felis catus) is among the most popular companion animals and most abundant carnivores globally. It is also a pet with an immense ecological footprint because even non-feral and food-subsidized cats can be prolific predators. Whereas knowledge about the spatial behavior of individual domestic cats is growing, we still know little about how a local population of free-ranging pet cats occupies the landscape. Using a citizen science approach, we GPS-tagged 92 pet cats with outdoor access living in a residential area in southern Norway. The resulting position data allowed us to construct both individual home range kernels and a population-level utilization distribution. Our results reveal a dense predatory blanket that outdoor cats drape over and beyond the urban landscape. It is this population-level intensity surface—the “catscape”—that potential prey have to navigate. There were few gaps in the catscape within our residential study area and therefore few terrestrial refuges from potential cat predation. However, cats spent on average 79% of their outdoor time within 50 m to their owner’s home, which suggests that the primary impact is local and most acute for wildlife in the vicinity to homes with cats. We discuss the catscape as a conceptual and quantitative tool for better understanding and mitigating the environmental impact of domestic cats.

Estimating the Population of Unowned Free-Ranging Domestic Cats in Denmark Using a Combination of Questionnaires and GPS Tracking

The present study aimed (1) to estimate the size of the population of unowned free-ranging domestic cats in Denmark using a questionnaire survey combined with a GPS-tracking survey, and (2) to estimate the distribution of the population across different habitats. The questionnaires were circulated in 94 randomly selected parishes ranging across seven kinds of habitat. Using responses from five of the habitats, we estimated the population of unowned free-ranging cats nationally. In the other two habitats, questionnaire data were collected in a simpler way. The territory of 59 owned cats was estimated with GPS tracking to assess home ranges. Home range area was calculated using 95% Brownian bridge kernel density estimation (0.033–0.077 ± 0.011–0.023 km2, median ± SE). We estimated a population of unowned free-ranging cats in Denmark of 89,000 ± 11,000 (SE), with a mean density of 2 ± 0.3 (SE) cats per km2, living primarily in rural habitats. Approximately one-third of the cats were estimated to be socialised and two-thirds unsocialised. Our method may be suitable for use in other temperate areas facing problems with unowned free-ranging cats.

Feral Cats in the Subtropics of Australia—The Shamrock Station Irrigation Project

Environmental damage caused by the intensification of agriculture may be compensated by implementing conservation projects directed towards reducing threatening processes and conserving threatened native species. In Australia, feral cats (Felis catus) have been a ubiquitous threatening process to Australian fauna since European colonisation. On Shamrock Station, in the north-west of Western Australia, the Argyle Cattle Company has proposed intensifying agriculture through the installation of irrigation pivots. There is concern that irrigating land and storing agricultural produce may indirectly increase the abundance of feral cats and European red foxes (Vulpes vulpes) on the property, which in turn may negatively impact threatened bilbies (Macrotis lagotis) that also inhabit the property. Feral cat control is required under the approved management plan for this project to mitigate this potential impact. Our baseline study revealed a high density of feral cats on Shamrock Station (0.87 cats km−2) and dietary data that suggest the current native mammal assemblage on Shamrock Station is depauperate. Given the high density of feral cats in this area, the effective control of this introduced predator is likely to confer benefits to the bilby and other native species susceptible to cat predation. We recommend ongoing monitoring of both native species and feral cats to determine if there is a benefit in implementing feral cat control around areas of intensive agriculture and associated cattle production.

Long-Distance Movements of Feral Cats in Semi-Arid South Australia and Implications for Conservation Management

Simple Summary

To efficiently control invasive animals, it is vital to have knowledge about their behaviour, their movements and how they use the landscape. Unusual behaviour is normally excluded from datasets, as it is considered to be an outlier that may distort analyses. In our study, we present movement data from feral cats in the arid and semi-arid zones of Australia. Feral cats are a serious problem to the native wildlife of Australia and in many parts of the world. Cats are known to show fidelity to geographic areas and may defend them against other cats. Until now, research has focused on these areas, home ranges or territories, that feral cats need to survive and reproduce. We argue that a part of their movement behaviour, large journeys away from the area they normally use, has been overlooked and has been considered to be unusual behaviour. We explain why we think that this is the case and present examples from other studies additional to our data set to show that these long-distance movements are a regular occurrence. To achieve a better protection of native wildlife from predation by feral cats, we believe that these long-distance movements should be considered as part of the normal behaviour of feral cats when planning cat control operations.

Abstract

Movements that extend beyond the usual space use of an animal have been documented in a range of species and are particularly prevalent in arid areas. We present long-distance movement data on five feral cats (Felis catus) GPS/VHF-collared during two different research projects in arid and semi-arid Australia. We compare these movements with data from other feral cat studies. Over a study period of three months in the Ikara-Flinders Ranges National Park, 4 out of 19 collared cats moved to sites that were 31, 41, 53 and 86 km away. Three of the cats were males, one female; their weight was between 2.1 and 4.1 kg. Two of the cats returned to the area of capture after three and six weeks. During the other study at Arid Recovery, one collared male cat (2.5 kg) was relocated after two years at a distance of 369 km from the area of collar deployment to the relocation area. The movements occurred following three years of record low rainfall. Our results build on the knowledge base of long-distance movements of feral cats reported at arid study sites and support the assertion that landscape-scale cat control programs in arid and semi-arid areas need to be of a sufficiently large scale to avoid rapid reinvasion and to effectively reduce cat density. Locally, cat control strategies need to be adjusted to improve coverage of areas highly used by cats to increase the efficiency of control operations.

Environmental and anthropogenic constraints on animal space use drive extinction risk worldwide

Animals require a certain amount of habitat to persist and thrive, and habitat loss is one of the most critical drivers of global biodiversity decline. While habitat requirements have been predicted by relationships between species traits and home-range size, little is known about constraints imposed by environmental conditions and human impacts on a global scale. Our meta-analysis of 395 vertebrate species shows that global climate gradients in temperature and precipitation exert indirect effects via primary productivity, generally reducing space requirements. Human pressure, however, reduces realised space use due to ensuing limitations in available habitat, particularly for large carnivores. We show that human pressure drives extinction risk by increasing the mismatch between space requirements and availability. We use large-scale climate gradients to predict current species extinction risk across global regions, which also offers an important tool for predicting future extinction risk due to ongoing space loss and climate change.

Does aerial baiting for controlling feral cats in a heterogeneous landscape confer benefits to a threatened native meso-predator?

Introduced mammalian predators can have devastating impacts on recipient ecosystems and disrupt native predator–prey relationships. Feral cats (Felis catus) have been implicated in the decline and extinction of many Australian native species and developing effective and affordable methods to control them is a national priority. While there has been considerable progress in the lethal control of feral cats, effective management at landscape scales has proved challenging. Justification of the allocation of resources to feral cat control programs requires demonstration of the conservation benefit baiting provides to native species susceptible to cat predation. Here, we examined the effectiveness of a landscape-scale Eradicat® baiting program to protect threatened northern quolls (Dasyurus hallucatus) from feral cat predation in a heterogeneous rocky landscape in the Pilbara region of Western Australia. We used camera traps and GPS collars fitted to feral cats to monitor changes in activity patterns of feral cats and northern quolls at a baited treatment site and unbaited reference site over four years. Feral cat populations appeared to be naturally sparse in our study area, and camera trap monitoring showed no significant effect of baiting on cat detections. However, mortality rates of collared feral cats ranged from 18–33% after baiting, indicating that the program was reducing cat numbers. Our study demonstrated that feral cat baiting had a positive effect on northern quoll populations, with evidence of range expansion at the treatment site. We suggest that the rugged rocky habitat preferred by northern quolls in the Pilbara buffered them to some extent from feral cat predation, and baiting was sufficient to demonstrate a positive effect in this relatively short-term project. A more strategic approach to feral cat management is likely to be required in the longer-term to maximise the efficacy of control programs and thereby improve the conservation outlook for susceptible threatened fauna.

Managing feral cats through an adaptive framework in an arid landscape

Adaptive management is the systematic acquisition and application of reliable information to improve natural resource management over time. We have employed an adaptive management framework in the control and monitoring of feral cats (Felis catus) on the Matuwa Indigenous Protected Area over the past 16 years. We used 120 Reconyx PC900 camera-traps and a rapid survey technique called the cat track activity index (TAI) to determine if aerial baiting with Eradicat® was more efficient and/or cost-effective than track baiting plus leg-hold trapping. We found that aerial baiting at $0.54 per percent decrease in cat detections is more cost-effective than track-baiting alone at $0.56 per percent decrease in cat detections. Track baiting plus leg-hold trapping, however, is more cost-effective than aerial baiting alone at reducing the number of feral cats detections at $0.39 per percent decrease in cat detections. Aerial baiting plus trapping was the most effective method of suppressing feral cats in an arid landscape with 97.7% reduction in cat detections. Trapping reduced the proportion of the population made up of adult cats from 51.5% to 38.7%, which may influence the efficacy of Eradicat®. Additionally, we found that cats were twice as likely to be detected on spinifex sandplain habitats than stony or hardpan habitats. We make several recommendations for refining feral cat management programs and future research.

Space use and habitat selection of an invasive mesopredator and sympatric, native apex predator

BACKGROUND

Where mesopredators co-exist with dominant apex predators, an understanding of the factors that influence their habitat and space use can provide insights that help guide wildlife conservation and pest management actions. A predator's habitat use is defined by its home range, which is influenced by its selection or avoidance of habitat features and intra- and inter-specific interactions within the landscape. These are driven by both innate and learned behaviour, operating at different spatial scales. We examined the seasonal home ranges and habitat selection of actively-managed populations of a native apex predator (dingo Canis dingo) and invasive mesopredator (feral cat Felis catus) in semi-arid Western Australia to better understanding their sympatric landscape use, potential interactions, and to help guide their management.

METHODS

We used kernel density estimates to characterise the seasonal space use of dingoes and feral cats, investigate inter- and intra-species variation in their home range extent and composition, and examine second-order habitat selection for each predator. Further, we used discrete choice modelling and step selection functions to examine the difference in third-order habitat selection across several habitat features.

RESULTS

The seasonal home ranges of dingoes were on average 19.5 times larger than feral cats. Feral cat seasonal home ranges typically included a larger proportion of grasslands than expected relative to availability in the study site, indicating second-order habitat selection for grasslands. In their fine-scale movements (third-order habitat selection), both predators selected for roads, hydrological features (seasonal intermittent streams, seasonal lakes and wetlands), and high vegetation cover. Dingoes also selected strongly for open woodlands, whereas feral cats used open woodlands and grasslands in proportion to availability.

MANAGEMENT RECOMMENDATIONS

Based on these results, and in order to avoid unintended negative ecological consequences (e.g. mesopredator release) that may stem from non-selective predator management, we recommend that feral cat control focuses on techniques such as trapping and shooting that are specific to feral cats in areas where they overlap with apex predators (dingoes), and more general techniques such as poison baiting where they are segregated.

Effectiveness of the Felixer grooming trap for the control of feral cats: a field trial in arid South Australia

Abstract ContextFeral cats pose a significant threat to wildlife in Australia and internationally. Controlling feral cats can be problematic because of their tendency to hunt live prey rather than be attracted to food-based lures. The Felixer grooming trap was developed as a targeted and automated poisoning device that sprays poison onto the fur of a passing cat, relying on compulsive grooming for ingestion. AimsWe conducted a field trial to test the effectiveness of Felixers in the control of feral cats in northern South Australia where feral cats were present within a 2600-ha predator-proof fenced paddock. MethodsTwenty Felixers were set to fire across vehicle tracks and dune crossings for 6 weeks. Cat activity was recorded using track counts and grids of remote camera traps set within the Felixer Paddock and an adjacent 3700-ha Control Paddock where feral cats were not controlled. Radio-collars were placed on six cats and spatial mark–resight models were used to estimate population density before and after Felixer deployment. Key resultsNone of the 1024 non-target objects (bettongs, bilbies, birds, lizards, humans, vehicles) that passed a Felixer during the trial was fired on, confirming high target specificity. Thirty-three Felixer firings were recorded over the 6-week trial, all being triggered by feral cats. The only two radio-collared cats that triggered Felixers during the trial, died. Two other radio-collared cats appeared to avoid Felixer traps possibly as a reaction to previous catching and handling rendering them neophobic. None of the 22 individually distinguishable cats targeted by Felixers was subsequently observed on cameras, suggesting death after firing. Felixer data, activity and density estimates consistently indicated that nearly two-thirds of the cat population was killed by the Felixers during the 6-week trial. ConclusionsResults suggest that Felixers are an effective, target-specific method of controlling feral cats, at least in areas in which immigration is prevented. The firing rate of Felixers did not decline significantly over time, suggesting that a longer trial would have resulted in a higher number of kills. ImplicationsFuture studies should aim to determine the trade-off between Felixer density and the efficacy relative to reinvasion.

Integrating feral cat (Felis catus) control into landscape-scale introduced predator management to improve conservation prospects for threatened fauna: a case study from the south coast of Western Australia

Abstract ContextFeral cat predation has had a significant impact on native Australian fauna in the past 200 years. In the early 2000s, population monitoring of the western ground parrot showed a dramatic decline from the pre-2000 range, with one of three meta-populations declining to very low levels and a second becoming locally extinct. We review 8 years of integrated introduced predator control, which trialled the incorporation of the feral cat bait Eradicat® into existing fox baiting programs. AimsTo test the efficacy of integrating feral cat control into an existing introduced predator control program in an adaptive management framework conducted in response to the decline of native species. The objective was to protect the remaining western ground parrot populations and other threatened fauna on the south coast of Western Australia. MethodsA landscape-scale feral cat and fox baiting program was delivered across south coast reserves that were occupied by western ground parrots in the early 2000s. Up to 500000ha of national parks and natures reserves were baited per annum. Monitoring was established to evaluate both the efficacy of landscape-scale baiting in management of feral cat populations, and the response of several native fauna species, including the western ground parrot, to an integrated introduced predator control program. Key resultsOn average, 28% of radio-collared feral cats died from Eradicat® baiting each year, over a 5-year period. The results varied from 0% to 62% between years. Changes in site occupancy by feral cats, as measured by detection on camera traps, was also variable, with significant declines detected after baiting in some years and sites. Trends in populations of native fauna, including the western ground parrot and chuditch, showed positive responses to integrated control of foxes and cats. ImplicationsLandscape-scale baiting of feral cats in ecosystems on the south coast of Western Australia had varying success when measured by direct knockdown of cats and site occupancy as determined by camera trapping; however, native species appeared to respond favourably to integrated predator control. For the protection of native species, we recommend ongoing baiting for both foxes and feral cats, complemented by post-bait trapping of feral cats. We advocate monitoring baiting efficacy in a well designed adaptive management framework to deliver long-term recovery of threatened species that have been impacted by cats.

Pre-eradication assessment of feral cat density and population size across Kangaroo Island, South Australia

Abstract Context Feral cats (Felis catus) are a significant threat to wildlife in Australia and globally. In Australia, densities of feral cats vary across the continent and also between the mainland and offshore islands. Densities on small islands may be at least an order of magnitude higher than those in adjacent mainland areas. To provide cat-free havens for biodiversity, cat-control and eradication programs are increasingly occurring on Australian offshore islands. However, planning such eradications is difficult, particularly on large islands where cat densities could vary considerably. Aims In the present study, we examined how feral cat densities vary among three habitats on Kangaroo Island, a large Australian offshore island for which feral cat eradication is planned. Methods Densities were compared among the following three broad habitat types: forest, forest–farmland boundaries and farmland. To detect cats, three remote-camera arrays were deployed in each habitat type, and density around each array was calculated using a spatially explicit capture–recapture framework. Key results The average feral cat density on Kangaroo Island (0.37 cats km−2) was slightly higher than that on the Australian mainland. Densities varied from 0.06 to 3.27 cats km−2 and were inconsistent within broad habitat types. Densities were highest on farms that had a high availability of macropod and sheep carcasses. The relationship between cat density and the proportion of cleared land in the surrounding area was weak. The total feral cat population of Kangaroo Island was estimated at 1629±661 (mean±s.e.) individuals. Conclusions Cat densities on Kangaroo Island are highly variable and may be locally affected by factors such as prey and carrion availability. Implications For cat eradication to be successful, resources must be sufficient to control at least the average cat density (0.37 cats km−2), with additional effort around areas of high carcass availability (where cats are likely to be at a higher density) potentially also being required.

Topographic complexity potentially mediates cat predation risk for a critically endangered rodent

ContextThe niche reduction hypothesis (NRH) predicts that the realised niche of declining species is reduced by threats that are mediated by environmental, biotic and evolutionary processes, explaining why species decline in some locations but not others. The critically endangered central rock-rat (CRR) survives only in rugged mountain range habitat in central Australia and is highly vulnerable to cat predation. We predicted that cat density and ranging behaviour, and, hence, predation risk, is mediated by habitat complexity, thus explaining the mechanism maintaining the CRR refuge. AimsWe sought to determine whether cat densities were lower in the rugged CRR refuge than in an adjacent valley dominated by less complex rocky habitats and no longer occupied by CRRs. MethodsWe installed arrays of camera traps along two parallel mountain ranges in the refuge and in the intervening valley habitats. We identified uniquely patterned individual cats and compared spatially explicit capture–recapture (SECR) models to evaluate our hypothesis that cat density varies with topographic complexity. Key resultsThe dominant effect in all models was the significant negative relationship between cat detection probability and fine-scale topographic ruggedness. Two of the best three SECR models indicated lower cat densities and relative home-range sizes in the refuge than in the valley. In total, 17% of cats were detected in both habitat types. ConclusionsWe found some evidence that cat density and home-range size were mediated by habitat complexity. Further, the negative relationship between cat detection probability and topographic complexity suggests that cats spend less time foraging in CRR refuge habitat. ImplicationsCat management programs, aimed at reducing predation pressure on the CRR, must include the refuge and surrounding habitats to control cats that pose a threat to CRR subpopulations.

Using Genetics to Evaluate the Success of a Feral Cat (Felis catus) Control Program in North-Western Australia

Simple Summary

The management of invasive species is a major challenge for the conservation of biodiversity globally. One technique that has been widely used to control feral cats (Felis catus) and red foxes (Vulpes vulpes) in Western Australia is the aerial broadcast of toxic baits, but assessing its efficacy can be difficult. Here, we report on a method of evaluating the effectiveness of this method for the abatement of feral cats using genetic analysis techniques. However, our results were unable to provide robust evidence that, over a five-year program, baiting had a detrimental impact on both genetics and demography in this population, and the results were not significant. Monitoring the impact of control programs in this way may provide valuable information to managers on the effectiveness of their management strategy, but further refinement of the methodology is recommended.

Abstract

The feral cat has been implicated in the decline and extinction of many species worldwide and a range of strategies have been devised for its control. A five-year control program using the aerial broadcast of toxic Eradicat^® baits was undertaken at Fortescue Marsh in the Pilbara region of north-western Australia, for the protection of biodiversity in this important wetland area. This program has been shown to have had a significant detrimental effect on cats in this landscape, but the long-term impact is difficult to ascertain. We assessed population genetics across three cohorts of feral cats sampled as part of the control program. We also compared cat populations in natural habitats and around human infrastructure. A key challenge in any study of wild animal populations is small sample sizes and feral cats are particularly difficult to capture and sample. The results of this study superficially appear to suggest promising trends but were limited by sample size and many were not statistically significant. We find that the use of genetic techniques to monitor the impact of invasive species control programs is potentially useful, but ensuring adequate sample sizes over a long enough time-frame will be critical to the success of such studies.

An Evaluation of Systematic Versus Strategically-Placed Camera Traps for Monitoring Feral Cats in New Zealand

Simple Summary

Feral cats are detrimental to native biodiversity worldwide. In New Zealand, feral cats are well established across much of the pastoral landscape, including forested areas. Feral cats, like many carnivore species, are elusive in their nature, and often occur at low densities, making them difficult to detect. Camera traps are a useful, non-invasive monitoring device, capable of ‘capturing’ feral cats as they pass by. Although cameras provide a wealth of information about animals within their field of view; there remains much to be learned about optimal camera trap placement within a landscape, if maximizing detection probability is the objective. Here, we report the results of two methods of camera trap deployment within similar sites: (1) systematic deployment on a grid and (2) strategic deployment, predominantly favoring habitats with assumed higher cat activity. Using the Royle–Nichols abundance-induced heterogeneity model (RN), which assumes detection probability and animal abundance are linked, we found that more cats were detected by cameras at forest margins than in mixed scrub or open farmland (but only slightly more than in forest locations). If maximizing cat detections is the aim, we recommend that cameras should be placed at the edges of forests (including forest fragments) whenever feasible.

Abstract

We deploy camera traps to monitor feral cat (Felis catus) populations at two pastoral sites in Hawke’s Bay, North Island, New Zealand. At Site 1, cameras are deployed at pre-determined GPS points on a 500-m grid, and at Site 2, cameras are strategically deployed with a bias towards forest and forest margin habitat where possible. A portion of cameras are also deployed in open farmland habitat and mixed scrub. We then use the abundance-induced heterogeneity Royle–Nichols model to estimate mean animal abundance and detection probabilities for cameras in each habitat type. Model selection suggests that only cat abundance varies by habitat type. Mean cat abundance is highest at forest margin cameras for both deployment methods (3 cats [95% CI 1.9–4.5] Site 1, and 1.7 cats [95% CI 1.2–2.4] Site 2) but not substantially higher than in forest habitats (1.7 cats [95% CI 0.8–3.6] Site 1, and 1.5 cats [95% CI 1.1–2.0] Site 2). Model selection shows detection probabilities do not vary substantially by habitat (although they are also higher for cameras in forest margins and forest habitats) and are similar between sites (8.6% [95% CI 5.4–13.4] Site 1, and 8.3% [5.8–11.9] Site 2). Cat detections by camera traps are higher when placed in forests and forest margins; thus, strategic placement may be preferable when monitoring feral cats in a pastoral landscape.

Does aridity affect spatial ecology? Scaling of home range size in small carnivorous marsupials

The aim of our study was to determine how body mass affects home range size in carnivorous marsupials (dasyurids) and whether those species living in desert environments require relatively larger areas than their mesic counterparts. The movement patterns of two sympatric species of desert dasyurids (body mass 16 and 105 g) were investigated via radio-telemetry in southwestern Queensland and compared with published records for other Australian dasyurids. Both species monitored occupied stable home ranges. For all dasyurids, home range size scaled with body mass with a coefficient of > 1.2, almost twice that for metabolic rate. Generally, males occupied larger home ranges than females, even after accounting for the size dimorphism common in dasyurids. Of the three environmental variables tested, primary productivity and habitat, a categorical variable based on the 500 mm rainfall isopleth, further improved model performance demonstrating that arid species generally occupy larger home ranges. Similar patterns were still present in the dataset after correcting for phylogeny. Consequently, the trend towards relatively larger home ranges with decreasing habitat productivity can be attributed to environmental factors and was not a result of taxonomic affiliation. We therefore conclude that alternative avenues to reduce energy requirements on an individual and population level (i.e. torpor, basking and population density) do not fully compensate for the low resource availability of deserts demanding an increase in home range size.

The value of camera traps in monitoring a feral-cat and fox reduction program

Abstract ContextWe examined the effectiveness of camera traps to monitor the success of a feral-cat (Felis catus) and fox (Vulpes vulpes) reduction program near Ravensthorpe, Western Australia. AimsTo determine whether camera traps are an effective tool to measure a reduction in the abundance of F. catus and V. vulpes at a local scale. MethodsIn all, 201 Foxoff® baits (i.e. 1080) were laid along the edge of unsealed tracks for each of three periods (i.e. opened 13–15 May 2017, Period 1 closed 29–31 May 2017, Period 2 closed 12–13 June 2017, Period 3 closed 25–26 June 2017), and 98 bait sites were monitored by camera traps during each period. In addition, 150 baited cage traps were deployed to catch F. catus for the same three periods. Vulpes vulpes and F. catus were also shot in the adjacent paddocks before traps were opened and during the laying of traps and bait replacement. We used the first 13 days of camera-trapping data for each period to examine whether there was a significant reduction in V. vulpes and F. catus. Key resultsCamera traps recorded a significant reduction in V. vulpes images, but knock-down with Foxoff® baits was not as effective as in other programs, and there was no change in the measured abundance of F. catus. Numerous baits were taken and not recorded by camera traps. Multiple V. vulpes moved past or investigated, but did not take baits and a V. vulpes was recorded regurgitating a bait. ConclusionsCamera traps were not effective for recording bait-take events. Vulpes vulpes knock-down was low and slow compared with other studies, did not reflect the number of baits taken and Foxoff® baits appeared unpalatable or unattractive to many V. vulpes. ImplicationsCamera traps did not record a high proportion of bait-take, appeared to be insensitive to small changes in fox and cat abundance and Foxoff® baits were less effective in reducing the abundance of V. vulpes than in other studies.

Evidence of significantly higher island feral cat abundance compared with the adjacent mainland

Context Feral cats (Felis catus) impact the health and welfare of wildlife, livestock and humans worldwide. They are particularly damaging where they have been introduced into island countries such as Australia and New Zealand, where native prey species evolved without feline predators. Kangaroo Island, in South Australia, is Australia’s third largest island and supports several threatened and endemic species. Cat densities on Kangaroo Island are thought to be greater than those on the adjacent South Australian mainland, based on one cat density estimate on the island that is higher than most estimates from the mainland. The prevalence of cat-borne disease in cats and sheep is also higher on Kangaroo Island than the mainland, suggesting higher cat densities. A recent continental-scale spatial model of cat density predicted that cat density on Kangaroo Island should be about double that of the adjacent mainland. However, although cats are believed to have severe impacts on some native species on the island, other species that are generally considered vulnerable to cat predation have relatively secure populations on the island compared with the mainland. Aims The present study aimed to compare feral cat abundance between Kangaroo Island and the adjacent South Australian mainland using simultaneous standardised methods. Based on previous findings, we predicted that the relative abundance of feral cats on Kangaroo Island would be approximately double that on the South Australian mainland. Methods Standardised camera trap surveys were used to simultaneously estimate the relative abundance of feral cats on Kangaroo Island and the adjacent South Australian mainland. Survey data were analysed using the Royle–Nichols abundance-induced heterogeneity model to estimate feral cat relative abundance at each site. Key results Cat abundance on the island was estimated to be over 10 times greater than that on the adjacent mainland. Conclusions Consistent with predictions, cat abundance on the island was greater than on the adjacent mainland. However, the magnitude of this difference was much greater than expected. Implications The findings show that the actual densities of cats at local sites can vary substantially from predictions generated by continental-scale models. The study also demonstrates the value of estimating abundance or density simultaneously across sites using standardised methods.

Scale-dependent home range optimality for a solitary omnivore

Spatial and temporal heterogeneity are fundamental mechanisms structuring home ranges. Under optimality, an individual should structure their space use economically to maximize fitness. We evaluated support for three hypotheses related to range optimality in American black bears (Ursus americanus), predicting (a) range location on a landscape will correspond with high vegetation productivity, (b) increasing forest fragmentation will result in larger ranges, and (c) increasing proportion of forest and/or mean vegetation productivity will result in smaller ranges. We used black bear radio telemetry data from Michigan (2009-2015), Missouri (2010-2016), and Mississippi (2008-2017), USA. Annual space use excluded winter, and we separated seasonal space use into spring, summer, and fall. We collected data from 143 bears (80 females, 63 males), resulting in 97 annual and 538 seasonal ranges. We used generalized linear mixed models to evaluate productivity (estimated through Normalized Difference Vegetation Index [NDVI]) selection, and range size (km2) variation between individuals. At the annual scale, black bears consistently selected areas with greater vegetation productivity than the surrounding landscape; yet selection weakened and was more variable seasonally. Opposite to our prediction, we found that increasing fragmentation consistently resulted in smaller ranges; non-forested land covers and forest edges might provide greater abundance or more diverse foods for bears. Ranges with a greater proportion of forest were smaller, likely reflecting an increase in food and cover which could reduce movements, yet there was no support for more productive ranges also being smaller as expected from an area minimizing strategy. Black bears displayed a scale-dependent space use strategy: at larger spatial and temporal scales, productivity acted as the strongest limiting factor and energy maximizing was the dominant strategy, while an area minimizing strategy was exhibited seasonally. We revealed consistent, scale-dependent responses by black bears to environmental conditions, demonstrating the intrinsic plasticity of this adaptable omnivore.

Evaluating the efficacy of a landscape scale feral cat control program using camera traps and occupancy models

The impact of introduced predators is a major factor limiting survivorship and recruitment of many native Australian species. In particular, the feral cat and red fox have been implicated in range reductions and population declines of many conservation dependent species across Australia, including ground-nesting birds and small to medium-sized mammals. The impact of predation by feral cats since their introduction some 200 years ago has altered the structure of native fauna communities and led to the development of landscape-scale threat abatement via baiting programs with the feral cat bait, Eradicat. Demonstrating the effectiveness of broad-scale programs is essential for managers to fine tune delivery and timing of baiting. Efficacy of feral cat baiting at the Fortescue Marsh in the Pilbara, Western Australia was tested using camera traps and occupancy models. There was a significant decrease in probability of site occupancy in baited sites in each of the five years of this study, demonstrating both the effectiveness of aerial baiting for landscape-scale removal of feral cats, and the validity of camera trap monitoring techniques for detecting changes in feral cat occupancy during a five-year baiting program.

Use of urban bushland remnants by the western ringtail possum (Pseudocheirus occidentalis): short-term home-range size and habitat use in Albany, Western Australia

Management of wildlife in habitats fragmented by urbanisation requires an understanding of a species’ habitat use. Known populations of the critically endangered western ringtail possum (Pseudocheirus occidentalis) are largely restricted to bushland remnants in rapidly urbanising areas of south-western Australia. Habitat use is thought to be driven by nutritional content, structure and connectivity of canopy vegetation. At the southernmost extent of the species’ range, habitat use is largely unknown, although it is expected to be different from previous descriptions due to differences in vegetation characteristics. We used VHF and global positioning system tracking collars to determine short-term home-range size, diurnal refuge use and night-time tree use of western ringtail possums in bushland remnants within Albany City. Possums had small home ranges (0.88 ha) that were negatively correlated with percentage canopy cover; used a variety of daytime refuges (predominantly dreys); and preferentially utilised marri (Corymbia calophylla) and jarrah (Eucalyptus marginata) at night. These results confirm that differences in habitat use among populations exist and suggests that the species is reasonably flexible in its use of habitat. Management of western ringtail possums needs to be population specific and will benefit from further examination of habitat use in the variety of occupied habitats.

Habitat as a mediator of mesopredator-driven mammal extinction

A prevailing view in dryland systems is that mammals are constrained by the scarcity of fertile soils and primary productivity. An alternative view is that predation is a primary driver of mammal assemblages, especially in Australia, where 2 introduced mesopredators-feral cat (Felis catus) and red fox (Vulpes vulpes)-are responsible for severe declines of dryland mammals. We evaluated productivity and predation as drivers of native mammal assemblage structure in dryland Australia. We used new data from 90 sites to examine the divers of extant mammal species richness and reconstructed historic mammal assemblages to determine proportional loss of mammal species across broad habitat types (landform and vegetation communities). Predation was supported as a major driver of extant mammal richness, but its effect was strongly mediated by habitat. Areas that were rugged or had dense grass cover supported more mammal species than the more productive and topographically simple areas. Twelve species in the critical weight range (CWR) (35-5500 g) that is most vulnerable to mesopredator predation were extirpated from the continent's central region, and the severity of loss of species correlated negatively with ruggedness and positively with productivity. Based on previous studies, we expect that habitat mediates predation from red foxes and feral cats because it affects these species' densities and foraging efficiency. Large areas of rugged terrain provided vital refuge for Australian dryland mammals, and we predict such areas will support the persistence of CWR species in the face of ongoing mammal declines elsewhere in Australia.

Habitat preference for fire scars by feral cats in Cape York Peninsula, Australia

Context Feral cats are implicated in the decline of terrestrial native mammals across northern Australia. Research in the Kimberley region of north-western Australia found feral cats strongly selected for fire scars when hunting, suggesting that intensifying fire regimes will have severe consequences for declining prey species. Aims We tested the generality of cat–fire interaction beyond the Kimberley, by measuring habitat selection of feral cats in relation to fire scars and habitat types in north-eastern Australia. Methods Our study was conducted at Piccaninny Plains Wildlife Sanctuary, Cape York Peninsula. We live-captured feral cats during the dry season of 2015, released them with GPS collars set to record fixes at 15-min intervals, and recaptured cats 4 months later. We created dynamic habitat maps of vegetation types, fire and wetlands, and compared cat habitat selection using discrete choice modelling. We also measured cat density from arrays of camera traps and examined cat diet by analysis of stomach contents. Key results We obtained GPS movement data from 15 feral cats. Feral cats selected strongly for recent fire scars (1 or 2 months old), but avoided fire scars 3 months old or older. Three long-distance movements were recorded, all directed towards recent fire scars. Cats also selected for open wetlands, and avoided rainforests. Density of cats at Piccaninny Plains was higher than recorded elsewhere in northern Australia. All major vertebrate groups were represented in cat diet. Conclusions We showed that feral cats in north-eastern Australia strongly select for recent fire scars and open wetlands. These results are consistent with those from the Kimberley. Together, these studies have shown that amplified predation facilitated by loss of cover is likely to be a fundamental factor driving mammal decline across northern Australia. Implications Reducing the frequency of intense fires may indirectly reduce the impact of feral cats at a landscape scale in northern Australia. We also suggest that managers target direct cat control towards open wetlands and recently burnt areas, which cats are known to favour.