Predation by feral cats Felis sylvestris catus is currently one hypothesized cause for the recent dramatic small mammal declines across northern Australia. We conducted a field experiment to measure the effect of predation by for this areas typically low-density cat populations on the demography of a native small mammal which due to the now natural scarce abundance of small mammals in the wild had to be reintroduced. We established two 12.5-ha enclosures in tropical savanna woodland on Wongalara Sanctuary, south of Arnhem Land in the Northern Territory. Each enclosure was divided in half, with cats allowed access to one half but not the other. We introduced about 20 individuals of Rattus villosissimus, a native rodent, into each of the four compartments (two enclosures x two predator-access treatments) and monitored rat demography by mark-recapture analysis and radio-tracking, and predator incursions by camera surveillance and track and scat searches. The data can be used for the mark-recapture analysis. The radio-tracking data and predator incursions data will be uploaded separately.
The Cat and Dingoes camera trap dataset was produced using a heat-in-motion cameras (Reconyx PC800 Hyperfire, Holmen, Wisconsin, USA) around the outside of the perimeter fences to detect predators. At least four (but up to six and always the same number of cameras at a time) cameras were placed as one camera installed at each side on the outside of the fences of each enclosure. Cameras were un-baited, to avoid attracting predators. This one file dataset contains the information on the presence/absence data of cats and dingoes on each day. 'Site' indicates the enclosure the camera was attached to ('Enclosure_I' or Enclosure_II'), 'Camera number' indicates which site the camera was on. Note that between October 2011 and April 2012, Enclosure II had two additional cameras (one facing the front gate and one additional monitoring the lower half of the back fence of the enclosure) which resulted in a total of six cameras for during that time. 'Date' indicates the date the photo(s) was/were taken, 'Photos_recorded' whether the camera was operational or photos were retained (e.g. one SD-cards was lost). And columns 'Dingo' and 'Cat' indicate whether these animals were present that day or not (na = no photos recorded, 0 = not present that day, 1 = present that day).
Credit
We at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
The authors thank Terry Mahney (DLRM) and Damien Stanioch (Territory Wildlife Park, TWP) for help with trapping rats on Quoin Island; Marissa Skeels (CDU), Damien Stanioch and Dr Steve Cutter (TWP) for the captive breeding of rats at TWP; Damien again and Eridani Mulder (AWC) for the translocation and release of rats at Wongalara. We would especially like to thank Heather and Chris Whatley, and Rod and Beth Beamont (AWC) for their support, and for building and maintaining the enclosures. UTas research assistants Kirsty Botha, Melissa Whatley, Sara Rathborne, Emma Tait, Lily Leahy and Tegan May, and many volunteers helped to monitor rats, cats and dingos at Wongalara. The study was funded by Australian Wildlife Conservancy and the Australian Research Council (LP100100033).
Purpose
Australia has already lost many mammal species to extinction. Dramatic and continuing declines of mammals across northern Australia mean that more species could be lost in the near future. There is still time to reverse these declines, but this will depend on a clear understanding of what is causing them. The project will use landscape-scale experiments to discover the factors that threaten mammals in northern Australia, focusing on predation by cats and its interactions with fire and grazing. The cameratrap dataset will provide knowledge to prevent extinctions and implement management for recovery.
Lineage
We constructed two 12.5-ha rat-proof enclosures, each divided in half, one half allowing cats and dingoes access (the fence was low enough at 0.9 m that cats could easily jump over) and the other half surrounded by a taller (2 m) electrified floppy-top fence to exclude mammalian predators. We refer to these as low-fence and high-fence treatments. To prevent small mammals from moving in or out of these treatments, a strip of smooth poly-belt, 40 cm high was attached to the inside lower section of all fences. The two enclosures were ~13 km apart. Enclosure I was in low (~10 m high) open woodland co-dominated by mixed Eucalyptus spp. and Terminalia spp., over a mixed Triodia spp. hummock grassland and mixed shrub understorey on sandy soils. Enclosure II was in similar low open woodland, but tree cover comprised Eucalyptus spp. and Cooktown Ironwood Erythrophleum chlorostachys, over a tussock grassland dominated by Chrysopogon spp., on sandy/lateritic soils. Mean percentage vegetation cover at rat height (10 cm above ground) was higher in Enclosure I than Enclosure II, but similar between the low and the high fence treatments within each enclosure. We introduced populations of the long-haired rat Rattus villosissimus (Status Least Concern, IUCN 2013), to all enclosure compartments for the purpose of this experiment. We collected 20 free-ranging R. villosissimus from Quoin Island about 530 km west of Wongalara, NT, in April 2011. To provide the numbers needed for introductions, these rats were initially housed and captive-bred, with handling kept to a minimum, at the Territory Wildlife Park before each release. In April 2012 we released 46 captive-bred rats as many as available into Enclosure I: 13 females and 10 males in the low-fence treatment and 11 females and 12 males in the high-fence treatment, with similar age composition in each group. In October 2011 we released 31 rats into Enclosure II, five rats (three females, two males) originating from Quoin Island, and the rest bred in captivity. Seven females and nine males were released into the low-fence treatment, and nine females and six males into the high-fence treatment. All were at least 1.5 months old and fully weaned; most (66%) were adults (> 60 g). All were marked with passive integrated transponder (PIT) tags. Rats of sufficient size (~ 100 g) were fitted with radio-collars (~ 4 g). In Enclosure I, seven rats (five males, two females) were radio-collared at release in each treatment. In Enclosure II, 10 rats (five males and five females) were radio-collared at release in each treatment. The fate of released rats was also monitored using live-trapping at intervals of approximately two months. Thirty-six aluminium box-traps (Elliott design) were arranged in a uniform pattern in 0.4-ha grids in each of the four enclosure halves. Traps were baited with a mixture of rolled oats and peanut butter, set in the late afternoon and checked at first light on the following day. Due to logistical constraints, the number of trapping sessions and their duration (number of nights) differed between enclosure sites, but not between the paired compartments (low fence and high fence) of each enclosure. In Enclosure I, trapping commenced two months after release of rats. Seven trapping sessions of between two and four consecutive trap nights were carried out (24 trap nights in total). In Enclosure II trapping commenced six months after the release of rats because of limited access during the wet season. In this enclosure, nine trapping sessions of between two and four consecutive nights occurred (29 nights in total). At each capture, individuals were identified, weighed and sexed. Body condition was scored using the method of Ullmann-Culleré & Foltz (1999), from category 1 = emaciated to 5 = obese. Recruits (i.e. individuals trapped in the enclosures that were not part of the initial release) were PIT-tagged at first capture.
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