Movements and Home Ranges of Crocodylus johnstoni in the Lynd River, Queensland

Abstract

Movements of Australian freshwater crocodiles, Crocodylus johnstoni, were examined by a mark–recapture study spanning 20 years in the Lynd River, Queensland. After adjustment for detection bias, there was a minor upstream direction to movements. Seasonal changes of location were not evident from field trips taken only twice yearly. Annual movements averaged less than 1 km except for those of pubescent males, which appeared to be nomadic. Creche dispersal was randomly directed but associated with a threshold in mass/length ratio. On average, males were found further from previous capture sites than were females. Adults of both sexes moved shorter distances than did immature crocodiles with a clear reduction in movements occurring as mass/length ratios approached 0·17 kg per cm snout–vent length. Reduced movement at that general size ratio probably indicated the onset of territoriality associated with maturity. Females usually remained near breeding sites even in years when they did not breed. Nomadic tendencies of pubescent males are probably associated with unsuccessful attempts at entering local dominance hierarchies. Linear home ranges were estimated to be 1·5–1·9 km for immature animals, 1·2 km for pubescent females, 30·3 km for pubescent males, 0·6 km for mature females and 1·6 km for adult males.