Great kangaroos are the largest members of the kangaroo family. They usually grow to about five feet (1.5 m) from nose to base of tail. Old males may exceed seven feet (2.1 m). The males are called boomers, or old men ; the females, flyers ; the young, joeys.

The kangaroos of Australia come in all different shapes and sizes. Some are very small. Rat kangaroos are the smallest. A full-grown rat kangaroo is smaller than a rabbit. It stands about a foot tall (30 centimeters). Then come the wallabies. Wallabies range in size from 1 to 5 feet (30 to 150 centimeters). Next come the wallaroos. The biggest family members are the red and gray kangaroos.

The red and gray kangaroos are the heaviest, strongest, and tallest marsupials. A red kangaroo can grow taller than any other kangaroo. “Big red” can grow to be 6 feet (1.8 meters) tall.

The red kangaroo is the largest kangaroo. It weighs as much as 190 pounds (86 kg). It inhabits the Australian plains. The eastern gray kangaroo weighs as much as 145 pounds (66 kg). It inhabits open woodlands of the Australian mainland and Tasmania. The euro, or wallaroo, which may be red, gray or black, weighs as much as 100 pounds (45 kg). It is common in Australia's rocky hills. It can survive for months without drinking because its body conserves water very efficiently.

The head of a great kangaroo resembles the head of a deer. A great kangaroo's forelegs and forepaws are small; its hind legs and feet are long and powerful. The toe next to the outer toe on each hind foot is armed with a large, strong claw. The tail is muscular and almost as long as the body. It is used as a prop when the kangaroo is standing and it helps the kangaroo maintain its balance while leaping.

Great kangaroos can attain speeds of up to 50 miles per hour (80 km/h) for short distances. Adults can leap as far as 30 feet (9 m), reaching a height of 10 feet (3 m). Great kangaroos live in herds, called mobs, which number from 5 to 100 animals. They eat grass, the leaves of shrubs and trees, and grains and fruits. The kangaroo has a multichambered stomach and thus can digest plant fiber high in cellulose. In times of drought it can therefore live on many drought-resistant plants other animals cannot digest.

Kangaroos are great hoppers. They do more than little bunny hops. Since kangaroos use their powerful hind legs and long feet to hop, their “hops” are more like “jumps.” They can hop fast and far.

One hop can carry a kangaroo three or four times its own length. The longest hop recorded is 43 feet (13.1 meters). Kangaroos can travel up to 50 miles (80 kilometers) an hour, but they cannot keep that speed up for too long.

When a kangaroo is not hopping, it rests on its big, long tail. The kangaroo uses its tail for pushing off. Its tail helps the kangaroo keep its balance, too.

A kangaroo’s small front legs are used to pull leaves from small plants or to dig into the ground for water. A kangaroo’s hind legs are very strong. They help a kangaroo push its entire body off the ground and into the air. These powerful legs allow the kangaroo to hop over objects equal to its own height.

Kangaroos are gentle animals. But if a kangaroo feels threatened, it uses its hind legs to defend itself. The kangaroo leans back on its long tail and strikes the enemy with its strong hind legs and sharp toenails. A single kangaroo kick can cause great harm to an enemy.

Typically, a kangaroo gives birth to a single joey four to five weeks after mating occurs. The birth of the joey is delayed, however, if there is a joey already occupying the mother's pouch and during periods of drought. In such cases, the embryo goes into dormancy and birth does not occur for as long as 11 months after mating. The newborn—blind, hairless, about one inch (2.5 cm) long and weighing about 1/30th of an ounce (1 g)—crawls to the pouch of its mother and attaches itself to a nipple. It remains attached to the nipple for several weeks, taking milk from the mother. After three months, the infant leaves the pouch for brief periods, diving back headfirst when danger threatens. It leaves the pouch permanently at about eight months, but continues to nurse for a few more months by putting its head inside the pouch. The mother sometimes nurses two young of different ages.

A female kangaroo gives birth to a joey one month after mating. She raises it alone. A newborn joey doesn't even look like a kangaroo. At birth, the joey is the size of a lima bean. Its body is mostly head and torso. It has no fur, and it cannot see or hear.

Right after birth, the joey crawls blindly into its mother’s pouch. It attaches itself to a teat and begins to drink its mother’s milk. The pouch is lined with fur. It’s a warm and cozy place to grow. The baby could not survive outside the pouch.

The joey enters the mother’s pouch head first, almost as if it’s doing a somersault. Once inside its mother’s pouch, the joey turns around. Then it pops its head out of the opening. Mom’s pouch is a safe place to hide!

A joey stays close to its mother until it is 2 or 3 years old. The joey continues to drink its mother’s milk until it is fully grown.

Kangaroos are generally gentle animals, but males sometimes fight each other for the females. Fighting commonly consists of wrestling, boxing, and kicking. Kangaroos can be tamed and trained to box playfully with humans.

The red and eastern gray kangaroos are hunted for their meat and hides. They are also killed by farmers because they eat crops.

Kangaroos are grazing animals. They eat grass and other small plants. Kangaroos usually gather in groups, or “mobs,” of up to a hundred animals. They live in many habitats, such as woodlands and grasslands. They can also be spotted on rocky hills, in deserts, and in trees.

Kangaroos are most active at night or early in the day. During the middle of the day, they rest under shady trees or bushes to stay cool.

Most people don’t think of kangaroos as tree climbers. But one kind enjoys living the high life. Tree kangaroos have smaller hind feet and bigger front feet than other kangaroos. A tree kangaroo is the only kind of kangaroo that can move one back leg at a time. This lets it walk along branches of trees, where it feeds on leaves or fruit. Sometimes a tree kangaroo jumps to the ground from the treetops. To get back into the tree, it jumps up about 20 feet (6.1 meters).