The impact of artificial watering holes

There is a commonly held view that kangaroo populations have increased because of human created waterholes in central Australia and the rangelands. Kangaroos may have expanded their range into areas of central Australia where artesian bores have provided water (Newsome 1980), but equally much well watered habitat has been lost to irrigated crops along inland rivers (Croft 2005). In the rangelands, however, it is known that water was widely distributed before European settlement (Landsberg et al. 1997).  
 
In many areas the rangelands are in fact covered by a vast network of drainage channels, ephemeral creeks, gilgais and clay pans, which can hold water for weeks and months after a modest rainfall. Many of these have silted up by the much accelerated erosion introduced by livestock (Fanning 1994, Condon 2002). In other cases, large watering holes have been supplemented but not necessarily replaced by earthen tanks, which lie on top of old springs or human created holes in existing swamps. Although adequate for kangaroos, these sources would not have been sufficient to service livestock.  
 
There are stark differences in uptake of water between kangaroos and livestock. Kangaroos have a long and narrow muzzle and tongue with which they lap water from small ephemeral sources, unattainable to the broad muzzled livestock which suck water (Croft 2005). If surface water is not available, kangaroos will dig the surface of creeks to expose water (Croft 2005). Further, kangaroos will readily drink muddy and algae infested water that is unacceptable to sheep (Croft 1985). A long term study of kangaroo population’s distribution in a rangeland landscape showed that the distribution was correlated to high quality forage and rest habitats, not watering holes (Montague-Drake and Croft 2004).  
 
There are also dramatic differences between kangaroo and sheep in terms of water requirements. The water turnover in summer is around 1 litre/day for a 25 kg Red Kangaroo or Euro and 1.75 litre/day for a 25 kg Eastern Grey Kangaroo (Hume 1999). In contrast, it is about 15-20 litre/day in summer for a sheep. A more recent study has identified the water turnover in the Red Kangaroo as 13% of sheep in moderate (non summer) conditions (Munn et al. 2008). This value may be almost doubled in the increased temperatures of summer. 
 
In fact, ecologists have found that the key predictor of kangaroo population dynamics is the previous year’s rainfall (Caughley et al. 1984, Bayliss 1985, Cairns and Grigg 1993), which determines the amount of food (grasses) that will be available to kangaroos. In a dry spell or drought, kangaroo populations decrease primarily because of large scale mortality of young (Shepherd 1987), followed by the weaker adult kangaroos due to starvation or associated conditions (pathogens).  
 
In conclusion, climatic conditions, not watering holes, seem to be the key determinant of kangaroo abundance in the rangelands. Comparison of current to pre-European-settlement kangaroo populations in the rangelands is tenuous at best, due to lack of empirical data (Baumber and Ampt 2006). However, the negative impact of hard hoofed livestock to the soils of the rangelands (Fanning 1994, Condon 2002) and to biodiversity (Fisher et al. 2003) is certain. The energetic requirement of sheep are up to three times that of kangaroos (Grigg 2002, Munn et al. 2008). Therefore, when considering degraded soil conditions and the biomass off-take by numerous livestock, then there is a reasonable possibility that kangaroo populations pre-European-settlement would have been more robust (excluding the impact of commercial harvesting) than today (Auty 2004, Croft 2005). 
 
Acknowledgement - thank you to Dr David B Croft. Much of the information above was obtained from his work 'Going, Going, Gone?' (Croft 2005). 
 
Sources: 
Auty, J. 2004. Red plague grey plague: the kangaroo myths and legends. Australian Mammalogy 26:33-36. 
 
Baumber, A., and P. Ampt. 2006. Book Review of Kangaroos: Myths and Realities. 2005. 3rd edition (1st edition Kangaroos - Our Wildlife Heritage – Not an exploitable resource. 1992; 2nd edition The Kangaroo Betrayed. 1999.) Edited by Maryland Wilson and David B Croft. Published by Australian Wildlife Protection Council. Australian Zoologist 33:315-321. 
 
Bayliss, P. 1985. The population dynamics of red and western grey kangaroos in arid New South Wales, Australia. II. The numerical response function. Journal of Animal Ecology 54:127-135. 
 
Cairns, S. C., and G. C. Grigg. 1993. Population dynamics of red kangaroos (Macropus rufus) in relation to rainfall in the South Australian pastoral zone. Journal of Applied Ecology 30:444-458. 
 
Caughley, G., P. Bayliss, and J. Giles. 1984. Trends in kangaroo numbers in western New South Wales and their relation to rainfall. Australian Wildlife Research 11:415-422. 
 
Condon, R. W. 2002. Out of the West: Historical Perspectives on the Western Division of New South Wales. Lower Murray Darling and Western Catchment Management Committees. 
 
Croft, D. B. 1985. Inter- and intraspecific conflict between arid-zone kangaroos at watering points. Australian Wildlife Research 9:21-26. 
 
Croft, D. B. 2005. The Future of Kangaroos: Going, Going, Gone? Pages 223-243 in M. Wilson, and D. B. Croft, editors. Kangaroos Myths and Realities. The Australian Wildlife Protection Council Incorporated, Melbourne. 
 
Fanning, P. 1994. Long-term contemporary erosion rates in arid rangelands environments in western New South Wales, Australia. Journal of Arid Environments 28:173-187. 
 
Fisher, D. O., S. P. Blomberg, and I. P. F. Owens. 2003. Extrinsic versus intrinsic factors in the decline and extinction of Australian marsupials. Proceedings of the Royal Society London B 270:1801-1808. 
 
Grigg, G. C. 2002. Conservation benefit from harvesting kangaroos: status report at the start of a new millennium. A Paper to stimulate discussion and research. Pages 53-76 in D. Lunney, and C. Dickman, editors. A Zoological Revolution. Using native fauna to assist in its own survival. Royal Zoological Society of NSW, Mosman. 
 
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Landsberg, J., C. D. James, S. R. Morton, T. J. Hobbs, J. Stol, A. Drew, and H. Tongway. 1997. The effects of artificial sources of water on rangeland biodiversity. in E. A. a. CSIRO, editor. Canberra. 
 
Montague-Drake, R., and D. B. Croft. 2004. Do kangaroos exhibit water-focused grazing patterns in arid New South Wales? a case study in Stuart National Park. Australian Mammalogy 26:87-100. 
 
Munn, A. J., T. J. Dawson, S. R. McLeod, D. B. Croft, M. B. Thompson, and C. R. Dickman. 2008. Field metabolic rate and water turnover of red kangaroos and sheep in an arid rangeland: an empirically derived dry-sheep-equivalent for kangaroos. Australian Journal of Zoology 57:23-28. 
 
Newsome, A. E. 1980. The eco-mythology of the red kangaroo in central Australia. Mankind 12:327-333. 
 
Shepherd, N. 1987. Condition and recruitment of kangaroos. Pages 135-158 in G. Caughley, N. Shepherd, and J. Short, editors. Kangaroos their ecology and management in the sheep rangelands of Australia. Cambridge University Press, Cambridge.