Eastern Grey Kangaroo
(macropus giganteus)
Geographic Range
Eastern grey kangaroos can be found on the eastern coastlines of Australia, all of Queensland with the exception of western Cape York, South Wales, and parts of Tasmania, most notably the north eastern portion.
Habitat
Eastern grey kangaroos inhabit a wide variety of habitats ranging from open woodlands to grasslands. They can also be found in mountains with extensive forest cover. The habitats of this species are usually areas of high rainfall, but this can also range to semi-arid areas.
Physical Description
Eastern grey kangaroos are often confused with the western grey kangaroos, which were initially considered a subspecies of the eastern grey. While a stark contrast in fur color can be seen in the throat and other areas of the western grey, eastern grey kangaroos have a more even distribution in fur color. The faces of the two species differ in that the western grey has a darker complexion as opposed to the almost white face of the eastern grey. Eastern greys also lacks the white patch on the upper thigh which is characteristic of a western grey.
There is great sexual dimorphism in size, with the males ranging from twice to three times the mass of an average female. Eastern grey kangaroos on the coastline will usually exhibit lighter colored fur than those inland, which are considerably darker in color. Eastern greys in Tasmania and the southern portions of Queensland also exhibit longer fur than in other areas. One other identifying characteristic is the black tip on the tails of this species. Females usually weigh up to about 40 kg, while males can weigh over twice as much, up to 90 kg. The standard metabolic rates of both eastern grey kangaroos and western grey kangaroos are lower than eutherians, although eastern grey kangaroos have a lower standard metabolic rate than western grey kangaroos.
Reproduction
Male eastern grey kangaroos often 'box' or exhibit other types of aggressive behavior to establish dominance. The dominant male is the most likely individuals to mate with a female in estrus. When a female eastern grey kangaroo reaches estrus, the male will approach and sniff various parts of her body including her pouch and urogenital area. He may also make clucking noises and paw her head and tail, a behavior characteristic of many kangaroo species.
Eastern grey kangaroos are seasonal breeders (spring and early summer), unlike some kangaroo species such as the red kangaroo or even the closely related western grey kangaroos, which breeds continuously as long as the conditions are good. The eastern grey kangaroo exhibits embryonic diapause, a condition in which development of the zygote is halted. This is similar to all kangaroo species with the exception of the western grey. The estrous period for eastern grey kangaroos lasts about 46 days, which is longer than the gestation period of 36 days. Sexual maturity for males is reached at about 20 months and for females at 17 months.
A joey, or baby kangaroo, usually stays in the pouch for 11 months during which it feeds from its mother's milk. It feeds for an additional 9 months, on average, from the mother's milk, although it leaves the pouch at 11 months. During this time, the mother provides protection and food and also guidance as the joey comes closer to becoming fully independent. An interesting point about the milk produced by the female kangaroo is that its notional content changes depending upon the nutrient requirements of the joey. Thus, the milk produced while the joey is exclusively inside the pouch differs from the milk produced when the joey spends part of its time outside the pouch. Females with joeys that are semi-independent to fully-independent from the pouch usually stay away from large groups, a behavior thought to avoid the risk of predation.
Lifespan/Longevity
Eastern grey kangaroos live for about 7-10 years in the wild, while there are records of those in captivity that have lived in excess of 20 years. Research in southern Queensland has shown that approximately 50% of young joeys fail to live to independence.
Behavior
Eastern grey kangaroos are a social species and usually live in small groups called 'mobs'. These 'mobs' include one dominant male, about 2-3 females with their young, and about 2-3 young males. As is common in all kangaroos, eastern greys move by hopping, usually around 9 meters every hop. Also characteristic of most kangaroos, the legs of eastern greys are designed so that they expend less energy the faster they are moving, which can be up to speeds of 30 miles per hour. Eastern grey kangaroos spend most of their day under the shade, then move out at dusk to feed until dawn.
Home Range
Eastern grey kangaroos do not have a broad home range like western grey kangaroos, which can have ranges in upwards of 500 ha. On average, eastern grey kangaroos have a mean home range of about 42.9 ha, but this value can range about 29.2 ha above and below this point. Density dependence and the availability of renewable resources may be the determining factors that limit the range of eastern grey kangaroos.
Communication and Perception
Both male and female eastern grey kangaroos usually communicate with each other and their young using clucking noises. When alarmed, they can also emit a guttural cough. This cough is also heard when males warn each other, fight, or display dominance. All grey kangaroos stamp their hind legs on the ground when they sense danger. This stamping, along with the guttural noise, sends a warning that travels quite distantly.
Food Habits
Eastern grey kangaroos are grazers and eat a wide variety of foliage ranging from grasses to forbs (broad-leaved herbs besides grass that grow on plains and meadows). The main choice of food, however, is grass, which grows on the plains that these kangaroos usually inhabit. In captivity, eastern greys may also feed upon fruits, although this is not part of the usual diet in the wild.
Predation
Eastern grey kangaroos have few natural predators. They have been hunted for thousands of years by Australian aborigines for fur and meat and later by European settlers. However, in the wild there are no species of animals that truly prey upon this species of kangaroo, with the exception of dingo’s. The effect of dingo’s are considered minimal.
Ecosystem Roles
Eastern grey kangaroos have a similar impact on the ecosystem as most other species of kangaroo. They are grazers and control the growth and spread of grass and other types of foliage. As with other grazers, this leads to soil dessication if unchecked, but their numbers are not great enough to be considered a serious ecological hazard.
Conservation Status
There are almost 2 million eastern grey kangaroos in Australia and the surrounding areas, and thus, are not considered to be in any immediate danger of extinction. There was a sharp decline in the popluation of eastern grey kangaroos in the late 1990's especially in Tasmania. However, these kangaroos are now protected by law by the Australian government and most of their range is now on private property. This has enabled the eastern grey kangaroo population to increase and continue growing. There is a large kangaroo industry in Australia but the number of kangaroos killed each year is striclty monitored and regulated by the Australian government.
Other Comments
Eastern grey kangaroos are the only species of kangaroo found in Tasmania. Their population took a sharp decline before laws were passed to protect eastern grey kangaroo populations.
http://animaldiversity.ummz.umich.edu