Movements and home ranges of radio-tracked Crocodylus porosus in the Cambridge Gulf region of Western Australia
Winston R. Kay
+ Author Affiliations
- Author Affiliations
Department of Zoology & Entomology, The University of Queensland, Brisbane, Qld 4072, Australia. Present address: Nature Conservation Division, Department of Conservation and Land Management, Locked Bag 104, Bentley Delivery Centre, Bentley, WA 6983, Australia. Email: winstonk@calm.wa.gov.au
Wildlife Research 31(5) 495-508 https://doi.org/10.1071/WR04037
Submitted: 10 October 2003 Accepted: 12 May 2004 Published: 13 December 2004
Abstract
VHF radio-tags were attached to 16 estuarine crocodiles that were tracked between October 2001 and May 2003. Male (n = 12) and female (n = 4) crocodiles exhibited distinctly different patterns of movement. Females occupied a small core linear range (1.3 ± 0.9 km) on the main river channel during the dry season and moved up to 62 km to nesting habitat during the wet season, returning to the same core area the following dry season. They occasionally made excursions away from their core areas during the dry season. Males moved considerable distances along the Ord River throughout the year. The largest range recorded was 87 km for a 2.5-m juvenile male. However, ranges of males did not appear to be related to body size, with the largest two ranges being recorded for the smallest (2.5 m) and largest (4.3 m) males tagged. Rates of movement of males did not differ significantly between three size classes of males but there were significant seasonal differences, with the highest mean rates of movement occurring during the summer wet season (4.0 ± 5.4 km day–1). However, males were quite mobile during the dry season and the highest rate of movement detected was 23.3 km day–1 for a 4.3-m male at the end of July. The highest rate of sustained movement was 9.8 km day–1 for a translocated 2.6-m juvenile male, which travelled 118 km in 12 days to return to the area of its capture. Neither males nor females showed exclusive habitat preferences for any of four broad riverine habitats identified on the Ord River. However, the three largest males had activity centres that they returned to frequently despite numerous excursions throughout the year, both up- and downriver. Males had substantial range overlaps with no obvious spatial partitioning, suggesting that territoriality is not an important behavioural characteristic of free-ranging male crocodiles along the Ord River.
Acknowledgments
This work was funded by the Department of Conservation and Land Management (CALM) and Lotterywest through a Gordon Reid Foundation grant to the Save Endangered East Kimberley Species (SEEKS) community group of Kununurra. Additional funding was provided by Australian Geographic. Thanks to numerous volunteers who assisted with fieldwork, particularly Chris Collins, Mike Osborn, Allan Pardoe-Bell and the SEEKS group. I also thank Nick Gales for lending a scanning receiver for an extended period; Derek Goddard, Jack Larsen and Tony Tully for equipment and assistance with helicopter tracking; and Gordon Grigg and Lyn Beard for equipment and advice with aerial tracking from fixed-wing aircraft. Thanks to the CALM office in Kununurra for logistical support during fieldwork, the Wyndham Crocodile Farm for lending their crocodile traps and the Department of Agriculture for the temporary loan of a boat at short notice. Finally, I thank Gordon Grigg, Hamish McCallum and Stuart Halse for their valuable comments during the preparation of this manuscript.
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