A physiological assessment of the use of water point closures to control kangaroo numbers
S. Underhill A , G. C. Grigg A C , A. R. Pople A B and D. J. Yates AA The Ecology Centre, School of Integrative Biology, The University of Queensland, Qld 4072, Australia.
B Land Protection, Department of Natural Resources, Mines and Water, GPO Box 2454, Brisbane, Qld 4001, Australia.
C Corresponding author. Email: g.grigg@uq.edu.au
Wildlife Research 34(4) 280-287 https://doi.org/10.1071/WR06041
Submitted: 14 April 2006 Accepted: 30 May 2007 Published: 28 June 2007
Abstract
Controlling kangaroo grazing pressure in national parks without harvesting or culling presents a significant challenge. Fencing off waterpoints is often tried or contemplated as a control measure, but its success obviously depends upon the extent to which kangaroos require access to discrete sources of drinking water. To assess the necessity for red kangaroos to supplement dietary water intake under different conditions by drinking free water, we followed changes in diet and in forage water and energy content as severe drought deepened at Idalia National Park in central Queensland from February to July 2002, the driest of 13 years for which records exist. Animals smaller than 15 kg in February and 25 kg in April did not need free water, but larger individuals needed to drink throughout the period. By July all animals needed to drink. The influence of body size arises because water requirements scale almost proportionally with body mass (M0.92) while energy requirements scale with a lower exponent (M0.74). Because of the sexual dimorphism in red kangaroos, adult females are therefore better able than adult males to survive water shortage. The results help define the constraints that physiological capabilities confer upon the usefulness of fencing off water points to control kangaroos. Smaller (younger) males and females could tolerate dry, cool conditions without drinking, even in this very dry year, but kangaroos of all body sizes needed to drink as the drought became more severe. The effectiveness of water closure will therefore depend on what forage is available, will target larger animals selectively, and will be most effective in semiarid areas like Idalia National Park in very dry years and late in the dry season when temperatures are rising and water requirements increase because of additional requirements for thermoregulation.
Acknowledgements
The study was supported by a post-graduate research grant from the School of Integrative Biology and conducted under a permit from Queensland National Parks and Wildlife Service. Col and Maureen Morgan at Idalia are thanked for their generous help throughout the study. Lyn Beard provided important logistical assistance and technical advice about bomb calorimetery.
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