There has been a rapid decline of small mammals across northern Australia, possibly driven by predation by feral cats and habitat simplification via changed fire regimes. It has been suggested, that arboreal mammals are being negatively affected by the fire-driven loss of large, hollow-bearing trees. We aimed to characterise the reliance of arboreal mammals on tree hollows as den sites on Melville Island. We radio-tracked 41 individuals of three species (brush-tailed rabbit-rat, black-footed tree-rat, and common brushtail possum), to 220 den sites. 30 of these individuals was tracked for a continuous 2-week period to assess frequency of tree hollow use. All three species almost exclusively denned (≥88% of den sites) in tree hollows (other sites such as hollow logs, Pandanus canopies, dreys etc). Larger tree hollows (entrance diameter >10 cm) were most common. Den trees were clustered, typically occurring within an area of just 0.9 ha-1. Although all none of our study species are considered obligate hollow users, we conclude that access to suitable tree hollows is essential to maintaining viable populations of these species. We speculate that the rapid decline of northern Australian arboreal mammals could have been amplified by contemporary fire regimes reducing the abundance of tree hollows.
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