A “joey” refers to the young of a marsupial, a diverse group of mammals with a unique reproductive process. While commonly associated with kangaroos, the term also applies to koalas, wallabies, wombats, and opossums. The marsupial pouch, or marsupium, is a specialized fold of skin on the mother’s abdomen. It serves as a secure nursery, providing warmth, protection, and nourishment for the developing young.
From Birth to the Pouch
Marsupials are born in an underdeveloped state after a short gestation period. For kangaroos, this period is around 28 to 33 days. The newborn joey is tiny, often compared to the size of a jelly bean, measuring about 2 centimeters long and weighing less than a gram. At this stage, it is blind, hairless, and has only partially formed hind limbs.
The joey possesses strong forelimbs with claws and an innate sense of direction. Immediately after birth, it instinctively crawls from the birth canal, through its mother’s fur, to the safety of the pouch. Once inside, the joey latches onto one of the mother’s nipples, which then swells to fill its mouth, securing it firmly in place.
Life and Development Inside the Pouch
The pouch serves as an external womb, providing a stable, protected environment for the joey’s development. Inside, the joey continuously nurses, relying on its mother’s milk for nutrients and immune defense. The mother’s strong sphincter muscle at the pouch opening helps keep the joey secure.
The joey undergoes significant growth and maturation. Its eyes and ears develop, fur grows, and limbs strengthen. Kangaroo joeys typically remain inside the pouch for at least six months. The pouch also helps regulate the joey’s body temperature, as newborns cannot do so independently.
The Initial Steps Outside
After several months, the joey begins its transition to the outside world. For kangaroos, this often starts around six months, when the joey first pokes its head out. These initial glimpses are brief, allowing the joey to observe its surroundings. As its fur develops, enabling temperature regulation, these head-poking episodes become longer.
Around seven to eight months, a kangaroo joey starts making short excursions out of the pouch. These first ventures are tentative, with the joey often stumbling as it builds leg strength. It quickly retreats to the pouch when startled or needing to feed or rest. Wallaby joeys also begin emerging around seven months, returning frequently. Koala joeys may start poking their heads out around five to six months, with full emergence and back-riding beginning around seven months.
Full Independence and Beyond
The period after initial emergence involves a progressive increase in time spent outside the pouch. The joey continues to nurse, often returning to the pouch for milk and refuge, even as it grows too large to fit entirely inside. For kangaroos, joeys might still suckle for several months after leaving the pouch permanently, sometimes up to 18 months for grey kangaroos.
During this stage, the joey learns essential survival skills from its mother, such as foraging for food and avoiding predators. The mother gradually encourages the joey to spend more time independently. Eventually, the joey no longer relies on the pouch for warmth, protection, or milk, marking its full independence.
Variations Among Marsupial Species
The timeline for joey development and departure from the pouch varies across marsupial species. Kangaroo joeys might stay in the pouch for 8 to 11 months before permanent departure, while koala joeys typically remain inside for six to seven months. Koalas continue to be dependent on their mothers for learning survival skills, riding on their backs, until 12 to 24 months.
Wombat joeys have a gestation of 20-22 days and stay in their backward-opening pouch for 4 to 10 months, averaging 8 months. They are fully weaned between 11 to 15 months and may stay with their mother for up to two years. Wallabies, like kangaroos, have a gestation of about 28 days, and their joeys begin to emerge around 5.5 to 7 months, with full independence taking several more months.