Despite their conspicuousness within urban environments, the ecology of commensal species is poorly understood. Urban environments are thought to provide abundant foraging and shelter resources for commensal species such as Black Rats Rattus rattus, but these assumptions are rarely tested. In this study, we tested whether Black Rats in the inner western suburbs of Sydney were shelter limited by placing piles of disused railway sleepers within small (<1 ha) areas of regenerating bushland surrounded by houses and railway lines. The piles of railway sleepers were intended to provide refuge habitat to small mammals and were monitored for 123 days using motion-sensitive cameras. Rat activity was positively associated with sites that had the log piles added, with no rat activity recorded at any of the control sites (without log piles), despite the presence of predators (domestic cats and foxes) at all sites. Rats rapidly investigated the log piles (mean time to first rat observation ± SE: 27.25 ± 14.34 days), but were only recorded intermittently over the monitoring period, suggesting that they did not permanently inhabit the sites. Our results suggest that black rats are likely to be limited by refuge opportunities within urban areas, and will rapidly investigate shelter opportunities. Removing available shelter habitat is likely to be an effective means of reducing rat populations within urban areas, particularly adjacent to bushland sites that are vulnerable to black rat invasion.

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