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An analysis of mark-recapture data for Rattus tunneyi in Kakadu National Park from a seven-year period was performed. Capture rates declined 500-fold during this period. The species exhibits a strong preference for riparian vegetation. The diet is primarily herbivorous, with little insect material. High-nutrient plant parts are generally chosen. Reproduction is most common in the wet season but some breeding extends throughout the year if unseasonal rain occurs during the dry season. Fire regime seems to have little effect on population numbers. The level of groundwater irrigating the riparian system and to a lesser extent current rainfall have a much stronger influence. Museum records show a contraction since European colonisation from a near-total continental distribution to one-seventh of its former distribution along the north-west Australian and southern Queensland coast. The contraction from the more-arid regions is likely to be due to the impact of introduced mammalian herbivores on the riparian habitats which previously functioned as refuge areas during periods of low water availability. Historically, R. tunneyi is likely to have fluctuated in distribution and abundance throughout the continent. In recent times, this has included irruptions into commercial crops in some areas. The loss of local refuges plus relatively poor powers of dispersal have resulted in the distribution now being fragmented, with the north-western and central east coasts of Australia providing the most significant habitat for the species.