Pests?

“The origins of the present kangaroo industry trace to rural support for it as self-funding pest control” (Australian Wildlife Management Society – position statement as of Feb 2009). State managed kangaroo harvesting programs have grown out of certain beliefs held by farmers in relation to kangaroos. The most common of these beliefs is that kangaroos are a major pest to crops. Another is that kangaroos compete with sheep and cattle for resources, thereby decreasing productivity. These beliefs are augmented by the widely held view that kangaroos overpopulate production zones due to increased food resources and increased artificial water points (put in place to support livestock) in these zones. State-managed kangaroo ‘harvesting’ (culling) programs were put into place (QLD, NSW, SA and WA) to alleviate the farmers’ concerns and manage the out of control self-funded kangaroo culling.

Over the years, studies have, for the most part, dispelled these beliefs as evidenced in the stated aims of the various state management programmes and national programme to manage the exploitation of kangaroos as sustainable resource and pest control where necessary (Deparment for Environment and Heritage 2007; Department of Environment and Climate Change 2007; Environment and Resource Management 2007). A six year study found only slight evidence of competition between sheep and kangaroos in times of extreme drought (Edwards et al. 1995; 1996). Another study in north-western New South Wales concluded that a decrease in wool productivity due to competition with kangaroos occurred only at low pasture biomass and high kangaroo densities (McLeod 1996). That study also concluded that Red Kangaroos have little or no impact on either the body mass or reproductive output of sheep or the growth and survivorship of lambs. In fact, it was found that Red Kangaroos “consistently avoid areas used by sheep” and that sheep have a negative impact on kangaroos.

Historically kangaroos were thought to have either the same requirements as sheep or up to 0.7 of the requirements. Recent studies indicate that kangaroos have only 0.3 of the energetic requirements (Munn et al. 2008). A recent assessments of the comparative contributions of sheep and kangaroos to total grazing pressure under more realistic values of dry sheep equivalents, comparative biomasses, and the lesser physical impact of kangaroos than sheep on soils and vegetation, concluded that "woolgrowers will not get the benefits they seek from a reduction in kangaroo numbers" (Grigg 2002).

A seminal study on the impact of Grey Kangaroos on crops established that more than 95% of crops in the wheat-belt are not visited by kangaroos, with most browsing occurring on crops located near the forest edge (Arnold 1990). While even this small amount of browsing is potentially problematic, it has been shown that when crops are around 400 m from the forest edge they are not affected at all by kangaroos, which rarely venture that distance away from the forest edge (Arnold et al. 1989).

A study of the impact of artificial water points on kangaroo densities and distribution identified high quality grazing and resting locations, not artificial water points, as the primary determinants of kangaroo distribution. The poor regeneration of vegetation around artificial watering points was attributed primarily to the impact of sheep grazing pressures 20 years after the removal of sheep (Montague-Drake and Croft 2004). Furthermore, the closure of artificial watering holes in outback Queensland during drought had no discernable effect on the densities of Red and Eastern Grey Kangaroos (Fukuda et al. 2010). These studies suggest that the reliance of kangaroos on the artificial watering holes has been overstated.

Further, despite the commonly held belief that kangaroos are pests that have experienced population explosions due to resource availability (Caughley et al. 1983; Grigg 1987; Pople et al. 2000), there are well-supported claims to the contrary (Senate Rural and Regional Affairs and Transport Committee 1998; Auty 2005; Croft 2005). These counter-claims suggest that historical records and current stocking capacities show that kangaroos may have been more widespread throughout Australia and present in greater numbers than they are today (Auty 2005; Croft 2005). The reality is that no one knows what the stable pre-harvesting populations were (Baumber and Ampt 2006).

References

Arnold, G. (1990). "Can Kangaroos Survive in the Wheatbelt? ." WA Journal of Agriculture 31(1090).

Arnold, G. W., D. E. Steven and J. R. Weeldenburg (1989). "The use of surrounding farmland by western grey kangaroos living in a remnant of wandoo woodland and their impact on crop production " Australian Wildlife Research 16: 85-93.

Auty, J. (2005). The Kangaroo Myths and Legends. Kangaroos Myths and Realities. M. Wilson and D. B. Croft. Melbourne, The Australian Wildlife Protection Council Incorporated: 62.

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.

Caughley, G., G. C. Grigg and J. Short (1983). "How many kangaroos?" Search 14: 151-152.

Croft, D. B. (2005). The Future of Kangaroos: Going, Going, Gone? Kangaroos Myths and Realities. M. Wilson and D. B. Croft. Melbourne, The Australian Wildlife Protection Council Incorporated: 223-243.

Deparment for Environment and Heritage (2007). The Kangaroo Conservation andManagement Plan for South Australia2008 – 2012, Government of South Australia.

Department of Environment and Climate Change (2007). New South Wales Commercial Kangaroo Harvest Management Plan 2007 - 2011. Sydney, NSW, Department of Environment and Climate Change.

Edwards, G. P., D. B. Croft and T. J. Dawson (1995). "The dietary overlap between red kangaroos (Macropus rufus) and sheep (Ovis aries) in the arid rangelands of Australia." Australian Journal of Ecology 20: 324-334.

Edwards, G. P., D. B. Croft and T. J. Dawson (1996). "Competition between red kangaroos (Macropus rufus) and sheep (Ovis aries) in the arid rangelands of Australia " Australian Journal of Ecology 21: 165-172.

Environment and Resource Management (2007). Wildlife Trade Management Plan for Export - Commercially Harvested Macropods – 2008-2012, Environment and Resource Management, Queensland.

Fukuda, Y., H. I. McCallum, G. C. Grigg and A. R. Pople (2010). "Fencing artificial waterpoints failed to influence density and distribution of red kangaroos (Macropus rufus)." Wildlife Research 36: 457-465.

Grigg, G. C. (1987). "Kangaroos - a better economic base for our marginal grazing lands." Australian Zoologist 24: 73-80.

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. A Zoological Revolution. Using native fauna to assist in its own survival. D. Lunney and C. Dickman. Mosman, Royal Zoological Society of NSW: 53-76.

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.

Pople, A. R., G. C. Grigg, S. C. Cairns, L. A. Beard and P. Alexander (2000). "Trends in the numbers of red kangaroos and emus on either side of the South Australian dingo fence: evidence for predator regulation?" Wildlife Research 27.

Senate Rural and Regional Affairs and Transport Committee (1998). Commercial Utilisation of Australian Native Wildlife, Executive Summary, Parliament of Australia, Senate.