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Radio-telemetry was used to identify the home range and refuge sites of two species of mouse inhabiting a semi-arid island off the Western Australian coast, in an effort to understand differences in their water metabolism. The native short-tailed mouse, Leggadina lakedownensis, had a median home range of 4.8 ha. This area increased during the non-breeding season (5.3 ha) compared with the breeding season (3.0 ha), but this difference was not significant. In contrast, the median home range for the house mouse, Mus domesticus, was smaller (2.8 ha), although this was variable. Core areas were best represented by the 75% and 60% isopleths for M. domesticus and L. lakedownensis, respectively. Core areas were greater in L. lakedownensis (1.0 ha) than in M. domesticus (0.8 ha). Furthermore, the degree of overlap in core areas was low for L. lakedownensis, but absent for M. domesticus. There was no evidence that M. domesticus used burrows as refuges. Instead, they sheltered in dense bushes above ground during the day where air temperatures were ameliorated by the cover. L. lakedownensis rested in burrows during the day where high air temperatures were maintained at a constant 28 degrees C, and a relative humidity of between 72-97%. Burrow morphology was simple and comprised two types: burrows with a single chamber, and those without a chamber, indicative of a solitary habit. These results suggest that a fossorial behaviour in L. lakedownensis may lower its water economy compared with M. domesticus, which shelters above ground.