suggested that the population inhabited few localised 'source' areas and a broad area of 'sink' habitat, with the latter only occupied after extraordinarily high rainfall events 24 leading to higher grass cover. A return to dry years and the consequent loss of cover (aided by an abundant rabbit population) and strong growth in predator numbers (feral 26 cats and small birds of prey) in response to the high number of field-rats appears to have facilitated the collapse. 28
Greater stick-nest rats were reintroduced to Heirisson Prong from Salutation Island at Shark Bay to establish the first mainland population in Western Australia in over 60 years. Forty-eight animals were transferred over two years from August 1999 to a 17-ha enclosure of natural vegetation that excluded foxes and feral cats. This refuge from introduced predators was located within a larger 1200-ha area where these predators were controlled. Stick-nest rats were able to disperse from the refuge to the wider area. The reintroduction was unsuccessful, with the last record in August 2007. Rats were reproducing in most years, yet only 28 recruits were detected over the reintroduction. Mean condition of rats was better at the reintroduction site relative to the source site. Survivorship of successive translocation cohorts was poorer than that of their predecessors, and survivorship of recruits was poorer than that of translocated animals. The most likely explanations for the decline are predation from monitors and small birds of prey within the refuge, and from monitors, small birds of prey and feral cats outside the refuge. An irruption of other rodents immediately before and coinciding with the reintroduction and building rabbit numbers likely contributed to elevated levels of predation from predators.
Context. The pale field-rat (Rattus tunneyi) is a small native rat that formerly had a wide distribution throughout Australia. It has suffered substantial range contraction since European settlement and is now largely absent from arid and semiarid Australia. In this biome, it was known to persist only at two Western Australian locations: Edel Land, on the south-western shore of Shark Bay, and islands off the Pilbara coast.Aims. We aimed to establish the extent of the species range at Edel Land, its habitat preference, the temporal stability of its populations with respect to rainfall, and threats to its persistence.Methods. We trapped at 54 sites to establish distribution and habitat preference, and re-trapped four of these sites at which R. tunneyi was present in each season for 2.5 years to establish trends in abundance.Key results. Trapping resulted in the capture of 45 R. tunneyi individuals across 17 of 54 sites (4104 trap-nights; 1.1% capture success). Rattus tunneyi typically occupied localised areas of dense shrubland, often in habitats with free water or near-surface moisture from drainage from high dunes allowing denser and taller vegetation and, at some sites, year-round growth of grasses or rushes. Regular re-trapping of four sites in each season (2002 -2004) suggested a declining population, probably owing to a sequence of dry years.Key conclusions. Rattus tunneyi at Shark Bay occurred only in localised mesic refuges, apparently dependent on seepage from high dunes generated by major inputs of rainfall from infrequent cyclones or sequences of high-rainfall years.Implications. This isolated population is likely to be threatened by browsing by feral goats, opening up otherwise densely vegetated habitats of refuge areas, and their trampling of R. tunneyi burrows; by the depletion of grasses from herbivory by European rabbits; and by the long-term impact of a drying climate. It is unlikely to persist without effective on-going management, particularly of the goat population.
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