1. Small mammal species are declining acrossnorthern Australia. Predation by feral cats Felis sylvestris catus isone hypothesised cause. Most evidence of cat impacts on native prey comes fromislands, where cat densities are often high, but cats typically occur at lowdensities on mainland Australia.
2. We conducted a field experiment to measurethe effect of predation by low-density cat populations on the demography of anative small mammal. We established two 12·5-ha enclosures in tropical savannain the Northern Territory. Each enclosure was divided in half, with catsallowed access to one half but not the other. We introduced about 20individuals of a native rodent, Rattus villosissimus, into each ofthe four compartments (two enclosures × two predator-accesstreatments). We monitored rat demography by mark-recapture analysis andradiotracking, and predator incursions by camera surveillance and track andscat searches.
3. Rat populations persisted over the durationof the study (18 months) in the predator-proof treatment, where wedetected no predator incursions, but declined to extinction in bothpredator-accessible compartments. In one case, cat incursions were frequentlydetected and the rat population was rapidly extirpated (<3 months); inthe other, cat incursions were infrequent, and the population declined moregradually (c. 16 months) due to low recruitment. We detected no incursionsby dingoes Canis dingo, the other mammalian predator in the area.
4. Synthesisand applications. This is the first study to provide direct evidence that catsare capable of extirpating small mammals in a continental setting, in spite oftheir low population densities. This finding supports the hypothesis thatpredation by feral cats is contributing to declines of small mammals innorthern Australia. The conservation management of native small mammals innorthern Australia may require intensive control of cat populations, includinglarge cat-free enclosures.