The Eastern Grey Kangaroo
The eastern grey kangaroo (Macropus giganteus) 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 (weight 145 lb.) and stands almost 2 m (6.6 ft.) tall, the scientific name, Macropus giganteus (gigantic large-foot), is misleading: the red kangaroo of the semi-arid inland is larger, weighing up to 90 kg.
The Eastern grey kangaroo is the second largest and heaviest living marsupial and native land mammal in Australia. An adult male will commonly weigh around 50 to 66 kg (110 to 146 lb) whereas females commonly weigh around 17 to 40 kg (37 to 88 lb). Large males of this species are more heavily built and muscled than the lankier Red Kangaroo and can occasionally exceed normal dimensions.
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.
Eastern 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.
Females 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.