A joey is the name given to a baby kangaroo, which belongs to the group of mammals known as marsupials. This term also applies to the young of other marsupials like koalas and wallabies. Kangaroos, found predominantly in Australia, employ a unique reproductive system where the young are born in an extremely underdeveloped state. This early birth necessitates the defining feature of marsupial life: an external pouch where development continues.
The Remarkable Birth
The gestation period for a kangaroo is remarkably short, lasting only about a month. The newborn joey is extraordinarily small, often compared to the size of a jellybean, weighing less than a single gram and measuring around two centimeters long. At birth, the joey is blind, hairless, and lacks the fully formed hind legs that characterize the adult kangaroo.
Despite its underdeveloped state, the joey possesses strong, clawed forelimbs, which it uses immediately after birth. The mother licks a pathway through her fur from the birth canal to the pouch opening. The tiny joey then begins an arduous, unaided crawl up the mother’s abdomen, using its front legs in a swimming motion to navigate the dense hair.
This perilous journey, which takes the joey about three minutes, is driven entirely by instinct and a strong sense of smell and direction. Once inside the pouch, the mother does not assist the joey, which must independently locate and latch onto a teat.
Life and Development in the Pouch
The mother’s pouch provides a protected, temperature-controlled environment for the joey’s continued growth. Upon arrival, the joey firmly latches onto one of the mother’s teats, which swells inside its mouth, securing it in place for several months. For the first few weeks, the joey remains permanently attached to the teat, receiving a constant supply of milk.
As the joey develops, it grows fur, its eyes open, and its body becomes more robust over several months. A key adaptation in the female kangaroo is asynchronous lactation, allowing her to produce two different types of milk simultaneously. She can nurse a tiny, newly attached joey on one teat with low-fat, high-carbohydrate milk, while an older joey drinks higher-fat, protein-rich milk from a different teat.
The duration of pouch life varies by species, but a joey typically remains inside for six to eleven months before beginning to emerge regularly. The mother is able to control the pouch muscles to keep the joey safely enclosed.
Transition to Independence
The first sign of the transition phase is when the joey begins to poke its head out of the pouch, observing the outside world around four to six months of age. Short excursions from the pouch start soon after, allowing the joey to practice hopping and to begin nibbling on grass and other vegetation. These initial trips are brief, and the joey quickly retreats to the safety of the pouch when alarmed.
The weaning process is gradual and continues long after the joey is too large to fit entirely inside the pouch. Even after spending most of its time outside, the joey will often stick its head back in to nurse. A red kangaroo joey may leave the pouch for good around eight months but continue to suckle for another three to four months.
Full independence is not achieved until the joey is much older, often between 12 and 18 months, depending on the species. By this point, the young kangaroo relies solely on grazing for nutrition and has established its own place within the mob.