Kangaroos are marsupials known for their distinctive locomotion and unusual reproductive cycle. They give birth to young that are born in a remarkably underdeveloped state, a process that separates them from placental mammals. This unique life history often leads people to wonder about the specific terminology used for the young of these iconic Australian creatures.
The Official Name
A baby kangaroo is formally known as a joey. This term is the widely accepted common name for their young, though it is not exclusive to kangaroos. The word “joey” is believed to have originated in early Australian slang, where it was used as a general name for any young animal, including human children. It has been in use for nearly 200 years to refer to the young of many Australian marsupials.
Development in the Pouch
The birth process for a joey is unlike that of most other mammals, following a very short gestation period of only 31 to 36 days. At birth, the joey is incredibly small, often described as being the size of a lima bean or jelly bean, weighing less than one gram. This tiny, blind, and hairless newborn immediately begins an arduous climb from the birth canal up the mother’s abdomen toward the pouch, using its relatively developed forelimbs and instincts.
Once inside the mother’s pouch, the joey securely attaches itself to one of the four teats, which then swells in its mouth to ensure a firm connection for constant feeding. The joey remains exclusively inside the pouch for approximately six months, where it continues to grow and develop fur, and its eyes open. After this initial period, the joey begins to make short excursions out of the pouch, returning quickly for warmth, protection, and nourishment.
The joey typically remains in and out of the pouch until it is between 10 and 12 months old, depending on the species, before leaving permanently. Even after leaving the pouch, the young kangaroo may continue to suckle from its mother for several more months. Female kangaroos can simultaneously nurse a newborn attached to a teat inside the pouch and a larger, older joey outside, providing each with a different composition of milk tailored to their developmental needs.
Other Marsupial Young
The term joey is used broadly across the marsupial infraclass, which includes many other pouched animals besides the kangaroo. For example, the young of wallabies, which are closely related to kangaroos, are also called joeys, exhibiting a similar pattern of underdeveloped birth and pouch residence. Koala infants are likewise referred to as joeys, staying within their mother’s backward-opening pouch for about seven months.
Even marsupials found outside Australia, like the American opossum, have young referred to as joeys. This shared name reflects the unifying reproductive strategy of the entire marsupial group.