User:Chad Zerr/Eastern grey kangaroo

Eastern grey kangaroos are gregarious and form open-membership groups. The groups contain an average of three individuals. Smaller groups join to graze in preferred foraging areas, and to rest in large groups around the middle of the day. 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. Eastern grey kangaroos adjust their behaviour 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.

Reproduction

Eastern grey kangaroos are polygynous which means that one male mates with multiple females. Males do a lot of intraspecific competition for mates which includes male-male fights to determine dominance between the two males. When a dominate male finds a female in estrus, he will court the female and eventually they copulate. [citation needed] After copulation, the male will guard the female from other males. This whole process from courting to when the male is done guarding the singular females is roughly and hour. [citation needed]

Females may form strong kinship bonds with their 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 reproduce in only one kind of habitat.

The female eastern grey 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 embryonic 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. Since lactation is very energy expensive, females that are lactating typically change some of their foraging habits. Some females will forage faster so they can tend to their joeys more, while others forage more aggressively so they can eat as much as possible.[Need citation] 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 conceive only 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. Female kangaroos with a joey often feed solitary in order to help separate themselves from the rest of the kangaroos in order to reduce predation. The joeys are heavily reliant on their mothers for about 550 days, which is when they are weaned. Females sexually mature between 17 and 28 months, while males mature at around 25 months.