Male kangaroos typically move large distances in search of mates and to establish territories far from where they were born, while females remain closer to home. However, a recent genetic study of kangaroos in the Blue Mountains shows the genetic structure of males and females is very similar. This unexpected pattern may be down to the environment they inhabit.
Eastern grey kangaroos (Macropus giganteus) are a well-known inhabitant of the east Australian coast but their distribution also stretches well into western New South Wales and Queensland as well as south-eastern South Australia. Throughout their distribution the habitat and environmental conditions differ, with access to food and water usually more variable in the west. As a result, kangaroos are often observed moving large distances to locate food and water. In addition, population sizes in the west are often less than on the coast, but numbers can also fluctuate dramatically in response to rainfall or drought.
The eastern grey kangaroo is one of the most heavily researched Australian marsupials but much of our knowledge comes from a small number of well-studied locations, mostly on the east coast. Kangaroos at these sites inhabit a variety of environments from grasslands to semi-natural pasture and woodlands but usually in quite flat areas. In parts of the Blue Mountains, however, kangaroos occur in hilly country in habitat that is mixture of former pasture and woodland surrounded by dense forest. In this study, we found that male and female eastern grey kangaroos at a site in the Blue Mountains have very similar patterns of dispersal. In fact, almost all the males appeared to come from the local area. This is unusual because male eastern grey kangaroos typically disperse and establish a new territory away from the area where they were born. The dense forest and large mountains that surround our study population most likely make it difficult for kangaroos to move in and out of the study area. This difference in habitat means they show different genetic patterns to other populations, with males and females appearing more similar in their movements.
The study also found that even though eastern grey kangaroos typically occur in groups, or mobs and are very social, the females in these groups did not appear to be close relatives. This differs from females in a Queensland population with similar habitat, where related females did appear more likely to associate and is more similar to populations studied in Victoria that inhabit open meadows. Both the Blue Mountains and Victorian populations occur at similar high densities and this may also influence dispersal behaviour. At high densities, females may be more likely to move further due to competition and unrelated females are therefore more likely to be close based on chance.
Despite their wide distribution, most genetic studies of eastern grey kangaroo have been of populations inhabiting similar environments along the east coast. We hope that future genetic studies will occur in the less well investigated populations west of the Great Dividing Range, where the environmental conditions are more variable and harsh.
Dr Linda Neaves, AMRI
Dr Mark Eldridge, Principal Research Scientist, AMRI
- Neaves, L.N., Roberts, M.W., Herbert, C.A. and Eldridge, M.D.B. 2017. Limited sex bias in the fine scale spatial genetic structure of the eastern grey kangaroo and its relationship to habitat. Australian Journal of Zoology early online