Kangaroo-vehicle collisions in Australia's sheep rangelands, during and following drought periods.

Abstract

The effects of roads on wildlife behaviour and ecological function are poorly known in arid Australia. The most obvious impact is roadkill from wildlife-vehicle collisions. Therefore we collected statistics on kangaroo-vehicle collisions, investigated the causal factors of these collisions, and related roadkill mortality to the population structure, size and distribution of four kangaroo species in two intensive six month studies during and following drought. The research was conducted along a 21.2 km sealed section of the Silver City Highway between Broken Hill and Tibooburra that passes through the University of New South Wales (NSW) Arid Zone Research Station at ‘Fowlers Gap’ in north-western NSW. The rate of roadkill was higher during drought (20.8 roadkills month-1) than non-drought (2.6 roadkills month-1). Affected species were red kangaroos (Macropus rufus), euros (Macropus robustus erubescens), western grey kangaroos (Macropus fuliginosus) and eastern grey kangaroos (Macropus giganteus). During drought, M. fuliginosus and M. giganteus were killed in lower proportions than their proportion in the source population, otherwise species were killed in proportion to their density along the road. There were no sex biases but male M. r. erubescens were much more likely to be beside the road than females and thus were killed more often during drought. The majority of roadkills were young individuals around 2 years old. Curves and stockraces along the road significantly increased the likelihood of roadkills. Likewise the frequency of roadkills was a function of the kangaroo population density along the road, night time traffic volume, low rainfall and higher vegetation cover and greenness along the road relative to surrounding areas. We evaluate the relationships between these causal factors and kangaroovehicle collisions, and discuss the possible effects of these collisions on kangaroo population structure under drought and post-drought conditions.