Kangaroos and wallabies (Macropus spp)
Several species of kangaroos and wallabies, Family Macropodidea, are at times considered to be overabundant and cause damage to production in Australia and environmental damage where they have been introduced into New Zealand. In Australia, 5 species are commercially harvested under a program to reduce their impact to acceptable levels. They are the red kangaroo Macropus rufus, eastern grey kangaroo M. giganteus, western grey kangaroo M. fuliginosus, the euro or wallaroo M. robustus and the whip-tailed wallaby M. parryi. Only the two major species, the red and grey kangaroo will be considered in more detail here. More information on these and other species can be found in the report by Tony Pople and Gordon Grigg (1999) and a report to NSW National Parks and Wildlife Service by Penny Olsen and Mike Braysher (2000).
In Australia, all kangaroos are protected native fauna under Commonwealth, state and territory legislation. However, certain species may be harvested to reduce the damage that they cause. Because some kangaroo products are exported, the Commonwealth requires that those state and territories that harvest and export kangaroo products, develop and have approved management programs for these commercially harvested species. The primary aim is to ensure that the harvested species are conserved over their entire range. The management programs must state:
• How the activities of shooters and dealers are to be controlled;
• How the size of the population is to be monitored;
• The regulation and checks to prevent illegal harvesting and over-harvesting; and
• Any other conservation practices recommended for the species.
After each management program is approved, conservative annual harvest quotas are set for each species. The potential impact of factors such as droughts and floods are factored into the assessment and the annual quotas are adjusted accordingly.
History and distribution
Red kangaroo (M. rufus)
Red kangaroos are widely distributed across mainland Australia except for the tropical far north and the south-west of Western Australia. They are an animal of the semi-arid and arid country as well as the mulga and mallee scrub. Most researchers and managers believe that there has been a significant increase in the numbers of red kangaroos since European settlement, primarily due to the provision of more water points, clearing of scrub to create pasture and control of its major predator, the dingo.
Eastern grey kangaroo (M. giganteus)
Eastern grey kangaroos are species that is mainly confined to the mallee and mulga scrub, woodland and forests of eastern Australia. They occur in most of Queensland except for Cape York, New South Wales, Victoria and north-eastern Tasmania. Like the red kangaroo, changes due to pastoralism have benefited the grey kangaroo.
Kangaroos are marsupials that typically have a short gestation period, approximately 30-35 days, giving birth to a young that completes most of its development attached to a teat in the pouch. This may be an adaptation to the harsh and variable conditions in which they live as the young may be abandoned at an early age under unfavourable conditions after relatively little maternal investment. Only one young is produced at a time but a second young is conceived soon after the birth of the previous young and held in embryonic diapause during lactation. Therefore, should a lactating young be lost for example due to poor environmental conditions, it can be replaced quickly. Thus kangaroos can rapidly recover their numbers after a drought.
Red kangaroos can breed all year depending on the environmental conditions as can grey kangaroos, although the latter species show a peak in births during summer. Both red and grey kangaroos are gregarious species forming sometimes large groups or mobs. The composition of the group is highly variable with the only stable combination being a female and her offspring.
Red kangaroos are more mobile than greys but even so, they are relatively sedentary with most animals moving less than 10 km. Both species occupy home ranges that extensively overlap those of other individuals. Red and grey kangaroos are specialist grass eaters with reds being slightly less specialist than greys.
Kangaroos damage fences and have a diet similar to that of stock. Studies indicate that in average to good seasons there is usually more food than either kangaroos or stock can consume. However, kangaroos may cause most damage to pastoralists going into and coming out of drought. While it is relatively simple to remove domestic stock from an area to conserve feed or to protect pasture, kangaroos remain and can defeat these attempts. Kangaroos can also cause environmental damage, especially if they are confined on reserved land and their numbers are allowed to increase unchecked. In New Zealand, there is considerable concern about the environmental damage that some species such as parma and brush-tailed rock wallabies are causing to island vegetation.
As described earlier, most damage mitigation in Australia is through commercial harvesting under approved management programs. Fencing has proved effective to protect crops and other assets in selected areas. Devices such as the Finlayson Trough have been tried to prevent kangaroos from accessing stock water but besides being considered inhumane, kangaroos can often circumvent the barriers. Contraceptives may be useful for controlling kangaroo populations in confined areas or in the peri-urban area. However, much more work is required including an assessment of their biological and ecological impacts, before they could be considered for wide-scale management of red and grey kangaroo populations.
- Olsen, P., and Braysher, M. 2000. Situation analysis report: current state of scientific knowledge on kangaroos in the environment, including ecological and economic impact and effect of culling. NSW NPWS, Sydney.
- Pople, T., and Grigg, G. 1999. Commercial Harvesting of Kangaroos in Australia. Environment Australia, Canberra.