Fossils reveal late Holocene diversity and post-European decline of the terrestrial mammals of the Murray–Darling Depression

Context Establishing appropriate faunal baselines is critical for understanding and abating biodiversity declines. However, baselines can be highly reliant on historical records that come from already disturbed ecosystems. This is exemplified in the Murray–Darling Depression bioregion of Australia, where European settlement (and accompanying marked land-management changes and the introduction of many species) triggered rapid declines and losses of native species, often before their documentation. Aims We aim to establish the mammal fauna present when Europeans settled the Murray Mallee and Murray–Darling Depression bioregion and determine the extent of mammal loss since European settlement. Methods We describe a dated vertebrate assemblage from Light’s Roost in the lower Murray Mallee region of South Australia. We compare our data with those of modern fauna surveys and historical records to document the extent of change in the mammal fauna since European settlement. Key results Radiocarbon ages showed that the assemblage was accumulating, at a minimum, within an interval from 1900 to 1300 years ago. Since this time, the Murray–Darling Depression has lost half of its flightless terrestrial mammals. Species lost include the mulgara (Dasycercus blythi/cristicauda), which places this taxon within only 40km of Lake Alexandrina, the hitherto-disputed type locality for D. cristicauda. Fossils provided the principal evidence for nearly half of the Murray Mallee fauna and over three-quarters of the fauna are represented in the fossil record. Conclusions Late Holocene assemblages provide important archives of species biogeography and diversity. Our revised faunal baseline indicated that the pre-European fauna of the Murray–Darling Depression was more diverse than hitherto understood and its reduction appears largely caused by the impacts of European settlement. Implications Baselines for species distributions derived from historical records and modern faunal surveys are likely to be incomplete and warrant revision, particularly for smaller and more cryptic species. Deficiencies in regional records mask the extent of mammal declines caused by European colonisation and associated agricultural practices, and thus vulnerability to anthropogenic disturbance.

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.

Multiple cameras required to reliably detect feral cats in northern Australian tropical savanna: an evaluation of sampling design when using camera traps

Context Feral cats are a major cause of mammal declines and extinctions in Australia. However, cats are elusive and obtaining reliable ecological data is challenging. Although camera traps are increasingly being used to study feral cats, their successful use in northern Australia has been limited. Aims We evaluated the efficacy of camera-trap sampling designs for detecting cats in the tropical savanna of northern Australia. We aimed to develop a camera-trapping method that would yield detection probabilities adequate for precise occupancy estimates. Methods First, we assessed the influence of two micro-habitat placements and three lure types on camera-trap detection rates of feral cats. Second, using multiple camera traps at each site, we examined the relationship between sampling effort and detection probability by using a multi-method occupancy model. Key results We found no significant difference in detection rates of feral cats using a variety of lures and micro-habitat placement. The mean probability of detecting a cat on one camera during one week of sampling was very low (p = 0.15) and had high uncertainty. However, the probability of detecting a cat on at least one of five cameras deployed concurrently on a site was 48% higher (p = 0.22) and had a greater precision. Conclusions The sampling effort required to achieve detection rates adequate to infer occupancy of feral cats by camera trap is considerably higher in northern Australia than has been observed elsewhere in Australia. Adequate detection of feral cats in the tropical savanna of northern Australia will necessitate inclusion of more camera traps and a longer survey duration. Implications Sampling designs using camera traps need to be rigorously trialled and assessed to optimise detection of the target species for different Australian biomes. A standard approach is suggested for detecting feral cats in northern Australian savannas.