OUR ECOSYSTEMS
human-animal interactions adaptation ecology vs. economy

Some Australians consider kangaroos to be pests. Surprised? So was I.

Kangaroos, posterchildren for the Australian outback, are considered by some to be pests in their homeland. In fact, most tourists have experienced the availability of kangaroo meat and leather in parts of Australia. How did this come to be?

image alt text

A few years ago, if someone asked me to say two things that I associated with Australia, it would have been kangaroos and koalas. These two animals have become iconic posterchildren for the great outback. What do tourists do when they go to Australia? Hold a koala, pet a wallaby, feed a kangaroo. I was offered all these opportunities when I stayed in Queensland, Australia for a semester abroad. Perhaps I was naïve, but I was surprised to find grocery stores and restaurants serving up kangaroo on the menu. We learned that kangaroos are actually considered a pest in parts of the outback. [Merriam-Webster definition of a pest: a plant or animal detrimental to humans or human concerns (as agriculture or livestock production).] Because kangaroos frequent grasslands and other open areas typical of farmland, farmers developed the perception that kangaroos compete with their livestock for food [1]. In fact, kangaroos narrowly missed a “noxious animal” labeling in the mid-1900s that would have required all landowners to remove kangaroos from their properties [2]. In modern day, approximately two million kangaroos are culled each year as part of pest control [3].

Kangaroos (Macropodidae) are native to the Australia continent, having separated from a possum-like ancestor 38-44 million years ago [4]. One might wonder, how can something so intrinsic (and majestic!) to the Australian landscape be considered a pest? Let’s put this in perspective. There are white-tailed deer (Odocoileus virginianus) that are native to North America (evolved ~3.5 million years ago) [5]. Many Americans are familiar with the idea that deer can be pests. When high in numbers, white-tailed deer have historically cost the timber industry millions by preferentially eating tree seedlings and sprouts most desirable for timber production [6]. Culls and other control methods have been suggested for white-tailed deer to decrease damage costs. Essentially, Australians view kangaroos in the same way Americans view deer. In that context, perhaps it is not so surprising how kangaroos came to be considered pests.

image alt text

Fig 1. Kangaroos grazing on sheep farmland in Australia. Photo by Janice.

In the case of kangaroos, is this title deserved? Maybe, maybe not. We often perceive animals based on how they directly affect us rather than how they affect the environment as a whole. Let’s examine the place of kangaroos and sheep (a prized Australian livestock) in both Australia’s ecology and economy.

Ecology:

Kangaroos are soft-footed herbivores that graze mainly on grasses and serve as a main prey of dingoes [7]. They are well-adapted to endure the heat and drought common to the Australian outback. For example, kangaroos will pant and lick their arms to utilize evaporative cooling (like when you sweat) and in extreme heat (e.g. 113˚F) can constrict their blood vessels to limit how much blood is available to be heated by the environment [8]. They replace water in their body at a rate of 0.40 gallons per day [9].

Sheep are nonnative herbivores that have a diet similar to kangaroos (e.g. grasses, forbs, shrubs) [7]. Sheep have hard hooves that have been observed to trample the natural landscape during moving and grazing [2]. Sheep are not as well-adapted for high water conservation and have a water turnover rate of 3.0 gallons per day [9].

Economy:

Kangaroos culled from farmland produce high quality meat and leather products, an industry approximated to value $100 million [10]; however, farmers do not receive money for kangaroos culled on their lands. Kangaroos are also important for tourism industry, though monetary value of their contribution to tourism is difficult to measure.

Sheep are an extremely important agricultural product in Australia; they garnered $5.2 billion for wool and meat products in 2014 [11].

image alt text Figure 2. Roo Out of Water (cartoon by Lian Guo).

The presence of kangaroos on farmlands causes understandable discomfort to Australian farmers. Any potential threat to a multi-billion dollar industry is significant enough to consider. Even so, there has not been research proving that the kangaroo diet decreases survival of Australian sheep and cattle. A recent study concludes that a large removal of kangaroos is unlikely to significantly improve quality of farmlands for livestock [9]. What’s interesting to me is that we as a society will preemptively label species as a pest and treat it as such before fully investigating whether that animal is truly a pest or not. Based on that classification, we justify removal of a species to reduce costs that have not yet been quantified. This is only one of many examples in history that we have placed our value of the economy before ecology. It will be interesting to see if this bias will cost us in the future. For instance, consider this: if the Australian climate follows predictions for longer and more severe dry conditions, it may no longer be possible to maintain sheep and cattle [12]. Without human intervention, it is likely that kangaroos would cope more successfully with the stresses of the Australian landscape than sheep would. In that case, would the outback-tolerant kangaroo be recategorized from pest to prized farm animal? Only time will tell.

References:

[1] Viggers, K. L., and J. P. Hearn. “The kangaroo conundrum: home range studies and implications for land management.” Journal of Applied Ecology 42, no. 1 (2005): 99-107.

[2] Lunney, Daniel. “A history of the debate (1948-2009) on the commercial harvesting of kangaroos, with particular reference to New South Wales and the role of Gordon Grigg 1.” Australian Zoologist 35, no. 2 (2010): 383-430.

[3] Wilson, G., P. Chardonnet, F. Lamarque, and M. Birkan. “Integrating Kangaroo (Macropus sp.) and other wildlife with agriculture in Australia.” Game and Wildlife Science 21, no. 4 (2004): 843-851.

[4] Burk, Angela, and Mark S. Springer. “Intergeneric relationships among Macropodoidea (Metatheria: Diprotodontia) and the chronicle of kangaroo evolution.” Journal of Mammalian Evolution 7, no. 4 (2000): 213-237.

[5] Anderson, Elaine. Pleistocene mammals of North America. Columbia University Press, 1980.

[6] Marquis, David A., and Ted J. Grisez. The effect of deer exclosures on the recovery of vegetation in failed clearcuts on the Allegheny Plateau. Vol. 270. Dept. of Agriculture, Forest Service, Northeastern Forest Experiment Station, 1978.

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

[8] Dawson, Terence J., Cyntina E. Blaney, Adam J. Munn, Andrew Krockenberger, and Shane K. Maloney. “Thermoregulation by kangaroos from mesic and arid habitats: influence of temperature on routes of heat loss in eastern grey kangaroos (Macropus giganteus) and red kangaroos (Macropus rufus).” Physiological and Biochemical Zoology 73, no. 3 (2000): 374-381.

[9] Munn, A. J., T. J. Dawson, S. R. McLeod, D. B. Croft, M. B. Thompson, and C. R. Dickman. “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, no. 1 (2009): 23-28.

[10] https://www.environment.gov.au/node/16678

[11] http://www.abs.gov.au/AUSSTATS/abs@.nsf/mf/7503.0

[12] Baettig, Michele B., Martin Wild, and Dieter M. Imboden. “A climate change index: Where climate change may be most prominent in the 21st century.”Geophysical Research Letters 34, no. 1 (2007).

More From Thats Life [Science]

Dialogue & Discussion