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Eastern grey kangaroos in Australia’s Kosciuszko National ParkThese eastern grey kangaroos taking a break on the grasslands of Kosciuszko National Park may look like hares or rabbits from a distance. But up close, a 6-foot-tall male eastern grey could look a person in the eye. Perhaps only koala bears rank higher as wildlife symbols of Australia, but we couldn’t resist featuring a photo of kangaroos to celebrate Australia Day today. Perhaps these ‘roos are waiting for the fireworks show?
Eastern grey kangaroo
The eastern grey kangaroo is a marsupial found in southern and eastern Australia, with a population of several million. It is also known as the great grey kangaroo and the forester kangaroo. Although a big eastern grey male typically masses around 66 kg and stands almost 2 m tall, the scientific name, Macropus giganteus, is misleading: the red kangaro…
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Eastern grey kangaroo
|Eastern grey kangaroo
Temporal range: 5–0 Ma Early Pliocene – Recent
|Eastern grey kangaroo range|
Like all kangaroos, it is mainly nocturnal and crepuscular, and is mostly seen early in the morning, or as the light starts to fade in the evening. In the middle of the day, kangaroos rest in the cover of the woodlands and eat there but then come out in the open to feed on the grasslands in large numbers. The eastern grey kangaroo is predominantly a grazer, eating a wide variety of grasses, whereas some other species (e.g. the red kangaroo) include significant amounts of shrubs in the diet.
BehaviorEastern grey kangaroos are gregarious and form open-membership groups. The groups are made up of 2-3 females and their offspring with the same number of males of which one is dominant. They exist in a dominance hierarchy and the dominant individuals gain access to better sources of food and areas of shade. However, kangaroos are not territorial and usually fight only when females are in estrous.
Eastern grey kangaroos adjust their behavior in relation to the risk of predation with reproductive females, individuals on the periphery of the group and individuals in groups far from cover being the most vigilant. Vigilance in individual kangaroos does not seem to significantly decrease when the size of the group increases. However, there is a tendency for the proportion of individuals on the periphery of the group to decline as group size increases. The open membership of the group allows more kangaroos to join and thus provide more buffers against predators.
ReproductionFemales may form strong kinship bonds with their female relatives. Females with living female relatives have a greater chance of reproducing. Most kangaroo births occur during the summer. Eastern grey kangaroos are obligate breeders in that they can only reproduce in one kind of habitat.
The female kangaroo is usually permanently pregnant, except on the day she gives birth; however, she has the ability to freeze the development of an embryo until the previous joey is able to leave the pouch. This is known as diapause, and will occur in times of drought and in areas with poor food sources. The composition of the milk produced by the mother varies according to the needs of the joey. In addition, the mother is able to produce two different kinds of milk simultaneously for the newborn and the older joey still in the pouch. Unusually, during a dry period, males will not produce sperm, and females will only conceive if there has been enough rain to produce a large quantity of green vegetation. Females take care of the young without any assistance from the males. The joeys are heavily reliant on their mothers for about 550 days which is when it is weaned. Females sexually mature between 17 and 28 months while males mature at around 25 months.
StatusIt is often said but not confirmed by evidence  that kangaroo populations have increased significantly since the European colonisation of Australia because of the increased areas of grassland (as distinct from forest), the reduction in dingo numbers, and the availability of artificial watering holes. The estimated population of the species Australia-wide in 2010 was 11.4 million. In some places the eastern grey is so numerous it causes overgrazing and some individual populations have been culled in some parts of Australia (See for example the Eden Park Kangaroo Cull). Despite the commercial harvest and some culls the eastern grey remains common and widespread. It still covers the entire range it occupied when Europeans arrived in Australia in 1788  and it often comes into conflict with agriculture as it uses the more fertile districts that now carry crops or exotic pasture grasses which kangaroos readily eat.
- Edwards,G. 1989. The interaction between macropodids and sheep: a review. pp.795-804 In: Grigg, G., Jarman. P and Hume, I. (Eds.) Kangaroos, wallabies and rat-kangaroos Volume 2. Surrey Beatty and Sons: Syndey
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