The western grey kangaroo is most active from late afternoon to early morning, resting during the day in the shelter of trees and shrubs. When moving slowly, such as when feeding, kangaroos show an unusual, ‘five-footed’ gait, balancing on the tail and forearms while swinging the hind legs forward (2). The diet of the western grey kangaroo consists mainly of grasses, as well as some herbs, leaves, tree bark and shrubs (2) (4), and it has a high tolerance to certain plant toxins (3).
A social species, the western grey kangaroo usually lives in groups, known as ‘mobs’, of up to 40 to 50 individuals. Old males are usually solitary (4). In the eastern part of its range, the species may mix with groups of eastern grey kangaroos, although the two usually occur separately due to differing habitat preferences (3). During the autumn and winter, male western grey kangaroos live in large groups away from the females and engage in threat displays and fights to establish dominance, with the largest, most dominant males having first access to the females in the spring (8). Although breeding may occur year-round, births usually peak between September and March, after winter rainfall has created maximum vegetation growth (2) (4) (8) (9). After a gestation of just 30 days (2) (4), the single, tiny newborn climbs unaided through the female’s fur and into the forward-facing pouch, where it attaches to one of four teats (4) (5). In common with other marsupials, most development occurs in the pouch, with the young, or ‘joey’, first emerging after around 280 days (8), and suckling until about 17 months old (4). Female western grey kangaroos become sexually mature at around 20 to 36 months, and males at around 20 to 72 months (2). Lifespan in the wild may be up to 20 years (4).
Somewhat unusually for a kangaroo, the female western grey kangaroo does not carry dormant embryos in the uterus while still suckling the first young in the pouch, a behaviour known as embryonic diapause (2) (8). Although the female may become receptive as early as 150 days after giving birth (2) (10), conception does not usually occur until there is enough time before birth for the first young to leave the pouch (2). However, if the first young dies in the pouch, the female can become receptive again in as little as eight days (2) (10). Although the lack of embryonic diapause means that the western grey kangaroo is unable, like other species, to recover quickly from drought by rapidly replacing lost young, its seasonal breeding is an advantage where winter rainfall and new spring growth are predictable (8).