Pictorial Guide to Kangaroo Population in Conservation Reserves

A pictorial guide on why it is sometimes necessary to reduce eastern grey kangaroo populations to protect other species of grassy ecosystems.

Figure 1: Many sites in the ACT are not subject to kangaroo culling, where abundant eastern grey kangaroos (450 per square kilometre) have few significant impacts and add to visitor enjoyment, such as the Yankee Hat walk in Namadgi National Park. Similar sites are found elsewhere throughout Namadgi and urban Canberra.

Figure 2: Plants and animals of the natural temperate grassland, whose numbers and distribution have greatly declined, like this Grassland Earless Dragon, need their habitat protected or they will soon be extinct. Vegetation removal is a threat, including from heavy grazing by kangaroos.

Figure 3: Eastern grey kangaroos are keystone species in the natural temperate grasslands. They are also ecosystem engineers. Either undergrazing or overgrazing by the kangaroos potentially threatens the survival of other grassland species.

Figure 4: Coorooboorama Raspy Crickets pictured on a native Blue Devil plant (Eryngium rostratum) above, are one of the species that construct the homes used by Grassland Earless Dragons in the natural temperate grassland. Both species depend on the vegetation layer of this rare ecological community. This cricket is only known to exist in the Canberra vicinity.

Figure 5: Golden Sun Moths (left) eat wallaby grass (Austrodanthonia) and are dependent on the natural temperate grassland. They have been declared critically endangered by the Commonwealth Government. The Perunga Grasshopper (right) is another grassland dependent species which has been declared threatened.

Figure 6: Kangaroo grazing at Majura Training Area (left) in the drought of 2006–07 removed the habitat of grassland earless dragons whose numbers plummeted. During the same period on the ‘Woden’ sheep property (right), controlled grazing left enough vegetation in place for Earless Dragons to persist in moderate numbers. Other threatened plants and animals also depend on the vegetation for protection, and would have been similarly affected.

Figure 7: (Left) Young eastern grey kangaroos are more appealing to the general public than the leser known threatened species of grassland-dependent plants and animals such as Grassland Earless Dragons, Striped Legless Lizards and Ginninderra Lepidium. Yet we have a responsibility is to protect them all. Eastern grey kangaroos are abundant, increasing and well protected in reserves in the ACT. However, they are impacting on grassland-dependent plants and animals in the few remaining ACT fragments of the natural temperate grassland. 

Figure 8: (Below) There are no known humane, non-lethal alternatives to kangaroo population reduction which are capable of meeting conservation obligations.  

Please refer to the ACT Kangaroo Management Plan for further information.  

Conservation and Kangaroos

The highest densities of kangaroos in the world (per square kilometre) are those in the valley-floor grasslands of Namadgi National Park and Tidbinbilla Nature Reserve in the ACT.

These populations of eastern grey kangaroos have few known environmental impacts, and provide a wonderful wildlife spectacle, and opportunities to observe the beauty of these kangaroos in close proximity. There would need to be very good reasons before anyone would propose culling in such sites, as is required by government policy for all kangaroo populations in the ACT.

Only Fragments Remain

Lowland Natural Temperate Grassland (LNTG) exists as a few fragments of ‘the most endangered vegetation type in Australia’ (Kirkpatrick 1995). Many species have permanently disappeared from LNTG and many others are facing extinction. The individual species tend to be lost from one fragment at a time. There is no longer any fragment with the full set of LNTG species. For example the Ginninderra Lepidium (an endangered plant) survives in only one site; and the Grassland Earless Dragon (an endangered lizard) is no longer found in Victoria or most of NSW, and survives in only three areas – Cooma (NSW), Majura Valley (ACT) and Jerrabomberra Valley (ACT). Many other LNTG species are also absent from apparently suitable sites.

Keystone Species and Environmental Engineers

Eastern grey kangaroos are a keystone species in the LNTGs. Their complete elimination may well result in a cascade of extinctions of threatened species, (unless they were replaced by another large grazing animal). On the other hand, too much grazing by kangaroos or other large animals, is also a threat. Prior to habitat fragmentation, heavy grazing may not have mattered much. Species disadvantaged by heavy grazing on one place could recolonise from elsewhere in the vast expanse of grassland. It is also possible that in original natural conditions, kangaroo grazing pressure was moderated by the effect of predators such as the Thylacine. But in the modern environment, it is impossible for threatened species to recolonise between fragments, and the moderating influence of the dingo, Thylacine and other top predators has been removed. Heavy grazing is the most likely cause of some of the previous losses from some fragments. The important point is that the remaining fragments of the original grasslands depend on moderate grazing. Either over-grazing or under-grazing is a threat (by kangaroos or other large animals).

Beauty or the Beast

Eastern grey kangaroos are among the most publicly appealing of mammals. Ginninderra Lepidium, Grassland Earless Dragons, Coorooboorama Raspy Crickets, Striped Legless Lizards, Perunga Grasshoppers, Golden Sun Moths and other grassland-dependent plants and animals are not as well known. Governments are legally and morally obliged to protect each species. Beauty is not a consideration.

This issue involves an abundant and (in the ACT) increasing species, which is well protected on some sites (eg in Namadgi National Park) and is not proposed to be removed from any site in the ACT. On a few special sites (the LNTG fragments), abundant kangaroos are reducing the populations of rare and declining species, which have been legally declared, in consultative processes, by multiple governments, to be threatened species. That declaration means in practice that special steps need to be taken, or those species will become extinct. Moderation of kangaroo grazing pressure on the LNTG fragments is one such step, and it is essential.