Resolving the value of the dingo in ecological restoration

There is global interest in restoring populations of apex predators, both to conserve them and to harness their ecological services. In Australia, reintroduction of dingoes (Canis dingo) has been proposed to help restore degraded rangelands. This proposal is based on theories and the results of studies suggesting that dingoes can suppress populations of prey (especially medium‐ and large‐sized herbivores) and invasive predators such as red foxes (Vulpes vulpes) and feral cats (Felis catus) that prey on threatened native species. However, the idea of dingo reintroduction has met opposition, especially from scientists who query the dingo's positive effects for some species or in some environments. Here, we ask ‘what is a feasible experimental design for assessing the role of dingoes in ecological restoration?’ We outline and propose a dingo reintroduction experiment—one that draws upon the existing dingo‐proof fence—and identify an area suitable for this (Sturt National Park, western New South Wales). Although challenging, this initiative would test whether dingoes can help restore Australia's rangeland biodiversity, and potentially provide proof‐of‐concept for apex predator reintroductions globally.     

Understanding predator densities for successful co‐existence of alien predators and threatened prey

The high failure rate of threatened species translocations has prompted many managers to fence areas to protect wildlife from introduced predators. However, conservation fencing is expensive, restrictive and exacerbates prey naïveté reducing the chance of future co‐existence between native prey and introduced predators. Here, we ask whether two globally threatened mammal species protected in fenced reserves, with a history of predation‐driven decline and reintroduction failure, could co‐exist with introduced predators. We defined co‐existence as population persistence for at least 3 years and successful recruitment. We manipulated the density of feral cats within a large fenced paddock and measured the impact on abundance and reproduction of 353 reintroduced burrowing bettongs and 47 greater bilbies over 3 years. We increased cat densities from 0.038 to 0.46 per square km and both threatened species survived, reproduced and increased their population size. However, a previous reintroduction trial of 66 bettongs into the same paddock found one red fox (Vulpes vulpes), at a density of 0.027 per square km, drove the bettong population extinct within 12 months. Our results show that different predator species vary in their impact and that despite a history of reintroduction failure, threatened mammal species can co‐exist with low densities of feral cats. There may be a threshold density below which it is possible to maintain unfenced populations of reintroduced marsupials. Understanding the numerical relationships between population densities of introduced predators and threatened species is urgently needed if these species are to be re‐established at landscape scales. Such knowledge will enable a priori assessment of the risk of reintroduction failure thereby increasing the likelihood of reintroduction success and reducing the financial and ethical cost of failed translocations.     

Feeling the pressure at home: Predator activity at the burrow entrance of an endangered arid‐zone skink

Habitat modification and invasive species are among the most important contemporary drivers of biodiversity loss. These two threatening processes are often studied independently and few studies have focused on how they interact to influence species declines. Here we assess the predation pressure placed on the threatened great desert skink (Liopholis kintorei) and how this interacts with fire‐induced habitat modifications. We collected daily track data of potential predators for 1 month at 30 great desert skink burrow‐systems where vegetation cover varied significantly after experimental burns. We used these data to evaluate potential predation pressure at the burrow‐system and assess whether fire influenced predator pressure. We supplemented this analysis by documenting predation via the inspection of large mammalian predator scats collected from great desert skink habitat. The level of feral cat activity at a burrow‐system entrance was significantly higher than that of any other potential predator, however fire had no effect on the visitation rates of feral cats, dingoes or large snakes to great desert skink burrow‐systems. The remains of great desert skink were found significantly more frequently in feral cat scats, compared to fox and dingo scats. We provide the first direct evidence that feral cats are a significant predator for great desert skink, thus supporting the hypothesis that feral cat predation is a key threatening process. Feral cat activity was not influenced by small‐scale experimental burns, however, this does not preclude an effect of larger scale fires and we recommend further research exploring this possible interaction.     

Direct evidence implicates feral cat predation as the primary cause of failure of a mammal reintroduction programme

As evidence mounts that the feral Cat (Felis catus) is a significant threat to endemic Australian biodiversity and impedes reintroduction attempts, uncertainty remains about the impact a residual population of cats following control will have on a mammal reintroduction programme. Also, behavioural interactions between cats and their prey continue to be an area of interest. Within the framework of an ecosystem restoration project, we tested the hypotheses that successful reintroductions of some medium‐sized mammals are possible in locations where feral cats are controlled (but not eradicated) in the absence of European Red Fox (Vulpes vulpes), and that hare‐wallabies that dispersed from their release area are more vulnerable to cat predation compared with those that remain at the release site. We used radiotelemetry to monitor the survivorship and dispersal of 16 Rufous Hare‐wallabies (Lagorchestes hirsutus spp.) and 18 Banded Hare‐wallabies (Lagostrophus fasciatus fasciatus) reintroduced to four sites within Shark Bay, Western Australia. Nearly all foxes were removed and feral cats were subject to ongoing control that kept their indices low relative to prerelease levels. All monitored hare‐wallabies were killed by cats within eight and 10 months following release. Significant predation by feral cats was not immediate: most kills occurred in clusters, with periods of several months where no mortalities occurred. Once a hare‐wallaby was killed, however, predation continued until each population was eliminated. Animals remaining near their release site survived longer than those that dispersed. The aetiology of predation events observed offers new insights into patterns of feral cat behaviour and mammal releases. We propose a hypothesis that these intense per capita predation events may reflect a targeted hunting behaviour in individual feral cats. Even where feral cats are controlled, the outcome from consistent predation events will result in reintroduction failures. Managers considering the reintroduction of medium‐sized mammals in the presence of feral cats should, irrespective of concurrent cat control, consider the low probability of success. We advocate alternative approaches to cat‐baiting alone for the recovery of cat‐vulnerable mammals such as hare‐wallabies.     

Not all predators are equal: a continent‐scale analysis of the effects of predator control on Australian mammals

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Apex predator suppression is linked to restructuring of ecosystems via multiple ecological pathways

Removal of apex predators can drive ecological regime shifts owing to compensatory positive and negative population level responses by organisms at lower trophic levels. Despite evidence that apex predators can influence ecosystems though multiple ecological pathways, most studies investigating apex predators’ effects on ecosystems have considered just one pathway in isolation. Here, we provide evidence that lethal control of an apex predator, the dingo Canis dingo, drives shifts in the structure of Australia's tropical‐savannah ecosystems. We compared mammal assemblages and understorey structure at seven paired‐sites. Each site comprised an area where people poisoned dingoes and an area without dingo control. The effects of dingo control on mammals scaled with body size. Where dingoes were poisoned, we found greater activity of herbivorous macropods and feral cats, a mesopredator, but sparser understorey vegetation and lower abundances of native rodents. Our study suggests that ecological cascades arising from apex predators’ suppressive effects on herbivores and mesopredators occur simultaneously. Concordant effects of dingo removal across tropical‐savannah, forest and desert biomes suggest that dingoes once exerted ubiquitous top–down effects across Australia and provides support for calls that top–down forcing should be considered a fundamental process governing ecosystem structure.     

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.     

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.     

Estimating abundances,densities, and interspecific associations in a carnivore community

Estimating population abundances, densities, and interspecific interactions are common goals in wildlife management. Camera traps have been used to estimate the abundance and density of a single species, and are useful for carnivores that occur at low densities. Spatial capture–recapture (SCR) models can be used to estimate abundance and density from a camera trap array when all, some, or no individuals in the population can be uniquely identified. These SCR models also estimate locations of individual activity centers, the spatial patterning of which could provide important information about interspecific interactions. We used SCR models to estimate abundances, densities, and activity centers of each of 3 carnivore species (i.e., dingo [Canis familiaris], red fox [Vulpes vulpes], and feral cat) using photographs from 1 camera trap array in southeastern Australia during September to November 2015. Some dingoes and feral cats were uniquely identifiable and therefore, we used a spatial mark–resight model for these species. We could not uniquely identify fox individuals, however, so we used a spatial unmarked (SUN) model for this species. Our estimated dingo density was 0.06/km². The fox (0.25/km²) and feral cat (0.16/km²) densities are within the ranges previously reported for these species in Australia. We obtained a relatively imprecise fox density estimate because we did not have detections of uniquely identifiable individuals; hence, the SUN model should be used as a last resort. We next modeled spatial dependence among the estimated activity centers for the 3 species using a spatial pair correlation function for a marked point process. Consistent with our expectations, the activity centers of dingoes and foxes were strongly negatively associated at distances of <1,000 m. Foxes and feral cats were also negatively associated at distances of <1,500 m. Surprisingly, dingoes and feral cats were positively associated at distances of >500 m, with no association evident at distances of <500 m. Our study extends the inferences that can be made from using a camera trap array and SCR methods to include spatial patterning and interspecific interactions, and provides new insights into the carnivore community of dingoes, foxes, and feral cats in southeastern Australia. © 2019 The Authors. The Journal of Wildlife Management Published by Wiley Periodicals, Inc.     

Prey use by dingoes in a contested landscape: Ecosystem service provider or biodiversity threat?

In Australia, dingoes (Canis lupus dingo) have been implicated in the decline and extinction of a number of vertebrate species. The lowland Wet Tropics of Queensland, Australia is a biologically rich area with many species of rainforest‐restricted vertebrates that could be threatened by dingoes; however, the ecological impacts of dingoes in this region are poorly understood. We determined the potential threat posed by dingoes to native vertebrates in the lowland Wet Tropics using dingo scat/stomach content and stable isotope analyses of hair from dingoes and potential prey species. Common mammals dominated dingo diets. We found no evidence of predation on threatened taxa or rainforest specialists within our study areas. The most significant prey species were northern brown bandicoots (Isoodon macrourus), canefield rats (Rattus sordidus), and agile wallabies (Macropus agilis). All are common species associated with relatively open grass/woodland habitats. Stable isotope analysis suggested that prey species sourced their nutrients primarily from open habitats and that prey choice, as identified by scat/stomach analysis alone, was a poor indicator of primary foraging habitats. In general, we find that prey use by dingoes in the lowland Wet Tropics does not pose a major threat to native and/or threatened fauna, including rainforest specialists. In fact, our results suggest that dingo predation on “pest” species may represent an important ecological service that outweighs potential biodiversity threats. A more targeted approach to managing wild canids is needed if the ecosystem services they provide in these contested landscapes are to be maintained, while simultaneously avoiding negative conservation or economic impacts.     

Habitat selection by feral cats and dingoes in a semi‐arid woodland environment in central Australia

Habitat use by feral cats and dingoes was examined within a heterogeneous semi‐arid woodland site in central Australia over 2 years. Density estimates of feral cats based on tracks were higher in mulga habitat than in open habitat. Isodar analysis implied that this pattern of habitat use by feral cats was consistent with the consumer‐resource model of density‐dependent habitat selection, which is an ideal free solution. The reason why mulga supported higher densities of feral cats was unclear. Foraging success of feral cats may be higher in the mulga because the stalk and ambush hunting tactics typically employed by felids are well suited to dense cover. Mulga may also have offered feral cats more protection from dingo predation. Dingo activity was distributed uniformly across habitats. The dingo isodar was statistically non‐significant, suggesting that habitat selection by dingoes was independent of density.     

The impact of grazing by macropods on coastal foredune vegetation in southeast Queensland

Abstract The extent of grazing by two macropodids, the agile wallaby (Macropus agilis) and the swamp wallaby (Wallabia bicolor) on coastal foredunes on South Stradbroke Island in southeast Queensland was investigated to determine potential impacts on the principal sand colonizing species, sand spinifex grass (Spinifex sericeus). Grazing on spinifex grass on the foredunes of South Stradbroke island can be attributed principally to agile wallabies. Foraging activity by wallabies was higher in areas of high spinifex abundance, however, grazing intensity and impact on spinifex was only important on foredunes with low spinifex abundance. Spinifex consumption by wallabies was also related to a number of factors, especially composition and structure of vegetation in adjacent habitats. Spinifex consumption increased when the abundance of ground cover components (grasses, sedges, forbs) in adjacent habitats was low and structural complexity was high. Grazing on foredunes by wallabies significantly affects the species composition of the foredune community by excluding the establishment of a number of perennial foredune plant species. This may have implications for community succession in coastal ecosystems.     

Home ranges of introduced mammalian carnivores at Trounson Kauri Park,Northland, New Zealand

Abstract

At Trounson Kauri Park, we monitored the movements of 21 feral cats (Felis catus), 11 stoats (Mustela erminea) and one male ferret (Mustelafuro). In feral cats, the average minimum home range was 446 ha (±82 SE) for 14 males, significantly larger than the average minimum of 117 ha (±40 SE) for seven females. In stoats the average minimum home range was 107 ha (±20 SE), for nine males compared with 81 ha (±31 SE) for two females. The single male ferret had a minimum home range of 197 ha. Adult male feral cats lived on apparently separate, non‐overlapping home ranges; females occupied exclusive home ranges which were overlapped by adult males; home ranges of sub‐adult male feral cats overlapped those of other sub‐adult male, adult male and female feral cats. The home ranges of two neighbouring male stoats overlapped, although their core ranges did not; both these and the ferret's home ranges overlapped those of the neighbouring feral cats. The feral cats were often located in cover in pastureland or near the edge of larger tracts of forest within their home ranges; stoats near waterways in the larger tracts of forest; and the ferret near the forest/pasture margins of Trounson Kauri Park. Our results suggest that control devices targeting all these species should be set at a minimum spacing of 800 m in order to put the majority of the resident and immigrant predators at risk.     

Ecologically functional landscapes and the role of dingoes as trophic regulators in south‐eastern Australia and other habitats

Large carnivores can play a pivotal role in maintaining healthy, balanced ecosystems. By suppressing the abundances and hence impacts of herbivores and smaller predators, top predators can indirectly benefit the species consumed by herbivores and smaller predators. Restoring and maintaining the ecosystem services that large carnivores provide has been identified as a critical step required to sustain biodiversity and maintain functional, resilient ecosystems. Recent research has shown that Australia's largest terrestrial predator, the Dingo (Canis lupus dingo), has strong effects on ecosystems in arid Australia and that these effects are beneficial for the conservation of small mammals and vegetation. Similarly, there is evidence from south‐eastern Australia that dingoes suppress the abundance of macropods and red Fox (Vulpes vulpes). It is likely that dingoes in south‐eastern Australia also generate strong indirect effects on the prey of foxes and macropods, as has been observed in the more arid parts of the continent. These direct and indirect effects of dingoes have the potential to be harnessed as passive tools to assist biodiversity conservation through the maintenance of ecologically functional dingo populations. However, research is required to better understand dingoes' indirect effects on ecosystems and the development of dingo management strategies that allow for both the preservation of dingoes and protection of livestock.     

Short‐term response of threatened small macropods and their predators to prescribed burns in subtropical Australia

Fire is an important ecological process that shapes vegetation structure and habitat for faunal assemblages globally. Prescribed burns are increasingly being used in conservation and management to restore fire regimes in fire‐suppressed vegetation communities. Small threatened macropods require structurally complex habitat that allows them to evade detection by predators. Given that fire can alter vegetation structure, it can be viewed as a strong ecological force in shifting the dynamics between predator and prey species. Previous studies in temperate Australia have shown that prescribed burns in the presence of European Red Fox (Vulpes vulpes) and feral Cat (Felis catus) can have negative impacts on small macropods and medium‐sized mammals. Post‐fire response of threatened small macropods and their predators has not been experimentally examined in subtropical Australia despite this region providing refugia for the Long‐nosed Potoroo (Potorous tridactylus) and Red‐legged Pademelon (Thylogale stigmatica). We conducted a before‐after‐control‐impact fire experiment at two paired sites after low–moderate intensity burns typical of cool season prescribed burns. We used camera trapping to investigate changes in activity of threatened small macropods and their predators. We also recorded vegetation change. Despite large reductions in ground and shrub cover, activity of small macropods and the Dingo (Canis dingo) did not change in response to fires. Therefore, the threat of dingo predation appears to have remained unchanged following the fires. Although feral cats and foxes were present, they showed negligible activity across our sites. Our study suggests that small‐scale patchy ecological burns may not lead to increased predation of small macropods in our landscape. We attribute this to sufficient post‐fire refugia and very low densities of foxes.     

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.     

Naiveté is not forever: responses of a vulnerable native rodent to its long term alien predators

Alien predators have wreaked havoc on isolated endemic and island fauna worldwide, a phenomenon generally attributed to prey naiveté, or a failure to display effective antipredator behaviour due to a lack of experience. While the failure to recognise and/or respond to a novel predator has devastating impacts in the short term after predators are introduced, few studies have asked whether medium to long term experience with alien predators enables native species to overcome their naiveté. In Australia, introduced dogs Canis lupus familiaris, foxes Vulpes vulpes and cats Felis catus have caused rapid extinctions and declines in small–medium sized native mammals since they were introduced ～150 years ago. However, native wildlife have had ～4000 years experience with another dog – the dingo Canis lupus dingo. Native bush rats Rattus fuscipes remain common despite predation from these predators. We predicted that prior experience with dingoes would mean that bush rats recognise and respond to dogs, but suspect that hundreds of years experience may not be enough for effective responses to cats and foxes. To test these predictions, we combined the giving‐up density (GUD) with analysis of remote camera footage to measure bush rat foraging and behavioural responses to body odour from dogs, foxes, cats and native spotted‐tail quolls Dasyurus maculatus. Bush rats responded strongly to dogs with increased GUDs, increased vigilance and decreased foraging. However, mixed responses to foxes and cats suggest that at least some individuals remain naïve towards these predators. Naiveté is not necessarily forever: alien predators devastate many native prey species, but others may learn or adapt to the new threat.     

The occurrence of the Broad‐toothed Rat Mastacomys fuscus in relation to feral Horse impacts

Feral Horse (Equus caballus) impacts in northern Kosciuszko National Park, New South Wales, Australia are directly occurring in habitat of the nationally threatened Broad‐toothed Rat (Mastacomys fuscus). This species is endemic primarily to the mountain regions of south‐eastern mainland Australia and Tasmania, with a disjunct population at Barrington Tops. The Broad‐toothed Rat's preferred habitat is being increasingly impacted by browsing and trampling associated with the expansion of feral horse populations. This study surveyed 180 sites supporting preferred habitat for this species to determine Broad‐toothed Rat presence and relative abundance in relation to the level of feral horse impacts within the reserve. There was a significant negative relationship between feral horse impacts and both Broad‐toothed Rat presence and abundance. No scats were identified at localities where feral horse impacts were severe, and at moderate horse impact sites, there was a proportion (34%) without scats found. Locations with low horse impacts had little impact on Broad‐toothed Rat occurrence. As feral horse populations increase, Broad‐toothed Rat populations may be further impacted. Such impacts will be due to the loss of vegetation cover from feral horse trampling and grazing, making animals more vulnerable to predation by predators or impacting on their ability to disperse to more suitable habitat. Habitat remnants and vegetation corridors along drainage lines require protection from feral horses to prevent localized extinctions of Broad‐toothed Rat.     

Does a top predator reduce the predatory impact of an invasive mesopredator on an endangered rodent?

The mesopredator release hypothesis (MRH) predicts that reduced abundance of top‐order predators results in an increase in the abundance of smaller predators (mesopredators) due to a reduction in intra‐guild predation and competition. The irruption of mesopredators that follows the removal of top‐order predators can have detrimental impacts on the prey of the mesopredators. Here we investigated the mechanisms via which the presence of a top‐order predator can benefit prey species. We tested predictions made according to the MRH and foraging theory by contrasting the abundances of an invasive mesopredator (red fox Vulpes vulpes) and an endangered prey species (dusky hopping mouse Notomys fuscus), predator diets, and N. fuscus foraging behaviour in the presence and absence of a top‐predator (dingo Canis lupus dingo). As predicted by the MRH, foxes were more abundant where dingoes were absent. Dietary overlap between sympatric dingoes and foxes was extensive, and fox was recorded in 1 dingo scat possibly indicating intra‐guild predation. Notomys fuscus were more likely to occur in fox scats than dingo scats and as predicted by the MRH N. fuscus were less abundant in the absence of dingoes. The population increase of N. fuscus following rainfall was dampened in the absence of dingoes suggesting that mesopredator release can attenuate bottom‐up effects, although it remains conceivable that differences in grazing regimes associated with dingo exclusion could have also influenced N. fuscus abundance. Notomys fuscus exhibited lower giving‐up densities in the presence of dingoes, consistent with the prediction that their perceived risk of predation would be lower and foraging efficiency greater in the presence of a top‐predator. Our results suggest that mesopredator suppression by a top predator can create a safer environment for prey species where the frequency of fatal encounters between predators and prey is reduced and the non‐consumptive effects of predators are lower.     

The diet of feral cats at New Island, Falkland Islands, and impact on breeding seabirds

We studied the diet of feral cats (Felis catus) on New Island, Falkland Islands, through the analysis of 373 scats collected during the austral summers of 2004/2005 and 2005/2006. The most frequent prey were three introduced mammals (house mice Mus musculus, ship rats Rattus rattus and rabbits Sylvilagus sp.) and the thin-billed prion Pachyptila belcheri (each season present on ca. 21% of the analysed scats). These represent the first systematic data on feral cat diet for the Falklands. A simple bioenergetics model suggests that cats could be eating in the region of 1,500–11,000 prions per season, representing <1% of the local adult and subadult population. Predation on other seabirds nesting on New Island (several penguin species, albatrosses and cormorants) was unimportant, with the possible exception of white-chinned petrels Procellaria aequinoctialis, which nest locally in very small numbers. For each prion eaten, cats were estimated to have killed 1.1–1.9 ship rats during the summer season, and probably more in autumn and winter. Knowing that ship rats are prion predators, it is conceivable that, on the whole, cats are having a positive impact on the prion population, a scenario predicted by general theoretical models. Thus, considering the available information, we would not recommend the implementation of any eradication programme on New Island that would target cats in isolation. Nevertheless, it would be prudent to consider some local action targeting cats and rats around the small New Island white-chinned petrel colony.