Kangaroo

Kangaroos are large, strictly herbivorous marsupials native to Australia. They are characterized by long, powerful hind legs with large feet, which they use to hop on the ground. In fact, kangaroos are the only large mammals that use hopping as their primary mode of locomotion.

Being marsupials, female kangaroos possess a characteristic pouch or marsupium for carrying their young. These animals also have a long, muscular tail that often acts like a fifth limb, alongside their two forelimbs and two hind limbs, while walking.

They are social animals that live in groups called mobs, courts, or troupes, comprising 10 or more individuals. As herbivores, they typically graze on grass but also consume the leaves of shrubs and herbs.

Species

The largest species of the family Macropodidae are commonly referred to as ‘kangaroos’. By this logic, there are 4 species of kangaroos.

• The red kangaroo (Osphranter rufus)
• The eastern grey kangaroo (Macropus giganteus)
• The western grey kangaroo (Macropus fuliginosus)
• The antilopine kangaroo (Osphranter antilopinus)

Macropodidae also comprises wallabies, wallaroos, and tree-kangaroos. However, they differ in size from the 4 species listed above and are not referred to as ‘kangaroos’.

While kangaroos are the largest in the family, the wallabies are the smallest. The tree-kangaroos and wallaroos are of intermediate size.

Description

Size: Height – About 5 ft 3 in (1.64 m)

Males of the largest species, the red kangaroo, typically stand up to 5.9 ft (1.8 m) tall when upright, while those of the smallest species, the antilopine kangaroo, average 3.9 to 4.3 ft (1.2 to 1.3 m) in height.

Weight: Between 40 and 200 lb (18.1 to 90.7 kg)

Body and Coloration: These mammals have stout, muscular bodies covered in short, dense fur. This fur ranges from reddish-brown in the red kangaroo to gray in the eastern and western gray kangaroos. On the belly, the fur is typically paler, often cream or light gray.

The most notable feature of kangaroos is their long, powerful hind legs with large feet, which help them hop on the ground. They also have a long and muscular tail. As marsupials, female kangaroos have a pouch or marsupium on their belly, in which the young complete their development after birth.

Male kangaroos are typically larger and more muscular than females.

Distribution

• The red kangaroo, the most widespread of all kangaroos, occupies most of inland Australia. However, it is absent from most of Victoria and Tasmania.
• The eastern grey kangaroo occupies the fertile eastern part of the country. Its range extends from the top of the Cape York Peninsula in northern Queensland down to Victoria, including areas of southeastern Australia and Tasmania.
• The western grey kangaroo is found in the southern part of Western Australia, South Australia, near the coast, and the Murray–Darling basin. Its highest population density is recorded in the western Riverina district of New South Wales, as well as in the west of the Nullarbor Plain in Western Australia.
• The range of the antilopine kangaroo is restricted to tropical north Australia, including the Northern Territory, Northern Queensland, and Northern Western Australia (Kimberley region).

Habitat

The red kangaroo occupies open plains and arid and semi-arid regions. On the other hand, the eastern grey kangaroo lives in woodlands and coastal plains.

The antilopine kangaroo inhabits open forests and tropical savannahs, while the western grey kangaroo lives in woodland, shrubland, and semi-arid regions.

Diet

Although all kangaroos are strict herbivores, their diet varies with species.

• The red kangaroo is a grazer and primarily feeds on fresh grass. However, it also eats forbs (herbaceous flowering plants) and leaves of shrubs.
• The eastern grey kangaroo favours grasses, too, but when food is scarce, it may feed on other plants and sometimes even fungi.
• The western grey kangaroo feeds on coarse grasses and shrubs, although in dry periods, it may also feed on tree bark.
• The antilopine kangaroo typically feeds on grasses, only occasionally switching to shrubs and herbs.

Behavior

• Kangaroos are social animals, living in groups called mobs, courts, or troupes, comprising 10 or more individuals. These groups are highly dynamic, with individuals frequently joining or leaving based on factors such as resource availability, mating opportunities, and changing environmental conditions. Typically, the group comprises females, juveniles, and a few adult males, including a single dominant male.
• Males engage in short-term and ritualized fights to assert their dominance and gain access to the females during the breeding season. In ritualized fights, the males stand upright and try to grasp each other with their forearms. They maintain balance on their muscular tails, kicking each other with their hind legs (boxing). The fight ends as one male backs down or hops away, accepting his defeat. In contrast, short-term fights include brief battles over space or food. These fights may escalate quickly, but they usually resolve quickly and do not involve forearm-locking.
• They typically move on the ground by hopping on two legs. During a hop, the kangaroo uses its powerful gastrocnemius muscles to lift the body off the ground. A smaller plantaris muscle is used for push-off. On average, kangaroos comfortably hop at about 22 km/h (14 mph), though the red kangaroo attains speeds of up to 70 km/h (43 mph) over short distances.
• At slow speeds, kangaroos switch to pentapedal locomotion, using their tail to form a tripod with their two forelimbs. The propulsive force that the tail generates is equivalent to that generated by the front and hind legs combined.
• These mammals are also adept swimmers and often flee into waterways when chased by a predator. This is a tactic to pursue the enemy into the water, after which the kangaroo may use its forepaws to hold the predator and drown it.

Lifespan

In the wild, kangaroos do not reach their maximum lifespan due to environmental stressors, such as predation and lack of resources. Depending on the species, they typically live between 9 and 15 years in the wild. However, in captivity, eastern and western kangaroos have been found to survive as long as 25 years.

Reproduction and Life Cycle

In kangaroos, the males and females form temporary consort pairs during the breeding season. Females in estrus typically roam around and try to attract the attention of the males through conspicuous signals. The males follow them, trying to sniff their urine and assessing their sexual receptivity. Once a receptive female is identified, the male approaches slowly to avoid startling her. If the female does stay on, the male continues by licking, pawing, and scratching her, followed by copulation. While larger males tend to females near estrus, smaller males tend to females farther from estrus. When males try to gain access to the female in estrus, they may engage in ritualized fights.

After a gestation period of 31 to 36 days, the female typically gives birth to one young or joey. At this stage, the tiny joey, about the size of a lima bean, has somewhat developed forelimbs and climbs to the marsupial pouch of its mother, attaching itself to a teat. The joey typically stays in the pouch for about 9 months (up to 320 days in the western grey kangaroo), after which it starts to venture out of the pouch for brief periods. The mother continues to feed the young till it is about 18 months old.

Female kangaroos are almost always carrying a developing embryo or a joey (except for the day they give birth), as they often mate again on the same day they give birth. If embryonic development begins before the previous joey can leave the pouch, the mother freezes the development (embryonic diapause). She may also resort to this diapause in conditions of drought or scarce resource availability.

Predators

Adult kangaroos are preyed upon by dingos, while joeys or weak individuals become targets of introduced mammals, like red foxes and feral cats. Additionally, large pythons and wedge-tailed eagles may kill kangaroo joeys, too.

Adaptations

• Since the antilopine kangaroo has a tropical distribution, it faces more heat and humidity when compared to the other species of kangaroos. As a possible adaptation to tackle this heat, the noses of male antilopine kangaroos swell behind the nostrils, expanding nasal passages and allowing them to release body heat.
• Kangaroos have large, elastic tendons in their hind legs. These tendons act like springs, storing elastic strain energy with each landing and releasing it during the next hop. Instead of relying primarily on muscle power, kangaroos use this spring-like action to propel themselves forward.
• Since kangaroos typically graze, they have developed a specialized dentition that is rarely found among mammals. For instance, they are equipped with incisors that crop grass close to the ground, allowing them to feed on low-lying grasses. Also, their molars are adapted for chopping and grinding fibrous plant material. 
• In kangaroos, the two sides of the lower jaw are not fused, resulting in the lower incisors being placed farther apart. This helps kangaroos take wider bites, gathering broader swaths of grass in each bite.