Numerous studies have detailed the home-range size of a variety of species. However, few have been able to determine the underlying contribution of species' traits (e.g. body mass and diet) versus the external environment (e.g. resource availability) on variation in home-range size. We investigated the importance of body mass and resource availability on the home-range size of a marsupial, the savanna glider (Petaurus ariel), in the tropical savannas of northern Australia. A strong rainfall gradient occurs over the region, resulting in substantial variation in resource availability throughout the geographic range of P. ariel. To determine P. ariel home-range size, we radio-tracked individuals from populations at the climatic extremes of the species’ geographic range, representing areas of high and low rainfall (mean annual rainfall: 1695 mm and 1074 mm, respectively). Additionally, we conducted spotlight surveys at each site to determine population density and collated live-trapping data to model the body mass of P. ariel over its geographic range. We found an almost 10-fold increase in P. ariel’s seasonal home-range size between the two study areas (high rainfall: 2.5 ha vs. low rainfall: 23.0 ha). Body mass (67.5 g vs. 101.1 g) and density (1.1 individuals ha–1 vs. 0.2 individuals ha–1) also varied significantly between the high and low rainfall populations, respectively. The mean seasonal home-range size of P. ariel was larger than any other similar-sized Australian Petaurid and was in the top 6% of home-range size, relative to body mass, of terrestrial, omnivorous mammals globally. The disproportionately large home-range size of P. ariel is most likely driven by low resource availability within the species' geographic range. Our findings highlight that when resources are limiting, home-range size can far exceed what is predicted by body mass and diet alone.