Diets and foraging behaviour of red and eastern grey kangaroos in arid shrub land: is feeding behaviour involved in the range expansion of the eastern grey kangaroo into the arid zone?

Eastern grey kangaroos (Macropus giganteus) have expanded into arid areas usually the habitat of red kangaroos (Macropus rufus). Extra watering sites for domestic stock is the suggested reason. However, changes in vegetation also have occurred due to grazing from domestic stock. We investigated the foraging strategies of M. giganteus and M. rufus in arid rangeland to see if these are involved in the range changes. Foraging patterns were similar, with both species mostly foraging at night; total feeding times were the same. M. giganteus and M. rufus had differing diets, though there was considerable overlap of 81 - 87%. Both species were highly selective, having similar narrow dietary niche breaths. Differences in plant preferences occurred and though both species had a preference for grass that of M. giganteus was higher. A larger foregut in M. giganteus reinforces its focus on grass. M. rufus also selected dicot forbs and malvaceous sub-shrubs. Both kangaroos showed avoidance of abundant chenopod shrubs (saltbushes and bluebushes) and trees. It is likely that the changes to arid-zone vegetation, with a shift to grass and annual dicot forbs, has been important for the expansion of M. giganteus, possibly combined with the greater availability of water.