Why Does a Kangaroo Have a Pouch?

Kangaroo

• With the exceptions of the North American opossum and the South American shrew opossum, marsupials are found exclusively in Australia, Tasmania, New Guinea and a few neighboring islands. There are many types of kangaroos. The red kangaroo is the largest species of kangaroo and the largest marsupial. The male can stand over 7 feet tall and weigh over 200 lbs. Female red kangaroos are slightly smaller, but they are faster than males. They can reach speeds over 30 miles per hour. The musky rat kangaroo is the smallest species.

Marsupials

• Biologists consider the marsupial reproductive system inefficient compared to placental mammals. Marsupial mothers don't develop the organ called the placenta, which carries and nourishes the fetus while it develops in the uterus. Instead, a developing marsupial fetus is nourished by fluids secreted directly from its mother's uterus. Marsupials are born tiny and underformed. In most species, they finish developing inside a fold of skin, or pouch, that covers their mother's teats.

Kangaroo Birth

• A kangaroo fetus develops in its mother's womb for about 30 to 40 days. When the baby kangaroo, or joey, is born, it is less than 1 inch long and weighs less than 1 oz. As soon as the baby is born, it crawls through its mother's fur toward the safety of her pouch. The mother avoids touching the tiny, delicate fetus. It guides the baby by carefully licking a path for it to follow. Once inside it clamps onto one of its mother's four teats and doesn't move for four or five weeks.

Development

• The baby is so small it can't suckle; instead, milk is squirted into its mouth by the contraction of muscles over the mother's milk-producing mammary glands. While the baby grows, older siblings that aren't fully weaned will periodically stick their heads into the pouch for milk. Each baby only suckles from one nipple. The mother's body regulates the formula of the milk according to each baby's needs. When the baby is about four months old, it leaves the pouch for short periods but returns for milk and transportation. At nine months, the joey permanently leaves the pouch.