The term “joey” refers to a young marsupial, a group of mammals characterized by giving birth to highly undeveloped young. The defining feature of most female marsupials is the marsupium, or pouch, a fold of skin on the abdomen that functions as a mobile, external nursery. The duration a joey remains in this protective environment is variable and depends on the species and their evolutionary strategies. This unique biological adaptation allows the mother to safeguard and nourish her offspring while continuing to move and forage.
The Joey’s Journey to the Pouch
Marsupial gestation is remarkably brief, with the young born in an almost embryonic state after a short time in the womb. A newborn kangaroo joey, for example, is typically the size of a jelly bean, hairless, blind, and weighs less than a single gram.
This tiny, fragile infant must immediately embark on a challenging journey that is self-propelled. The joey uses its relatively developed forelimbs and sharp claws to crawl, unaided, through the mother’s fur from the birth canal up to the pouch opening. This short but perilous climb is guided by instinct and the mother’s saliva, which she licks into a path.
Once inside the pouch, the joey’s immediate action is to locate and attach securely to a teat. The teat swells once it is in the joey’s mouth, forming a firm connection that ensures continuous feeding for the initial months. The joey remains fused to this milk source, completing the majority of its development within the pouch’s warm, regulated environment.
Key Developmental Milestones and Pouch Duration
The time spent inside the pouch is a direct function of the species’ size and life history, with large macropods having the longest duration. A Red Kangaroo joey will remain permanently attached to the teat for about 70 days, with total pouch life before permanent exit lasting approximately seven to nine months. In contrast, smaller wallaby species generally have a slightly shorter pouch duration, with their joeys leaving around six to eight months of age.
During this extended residency, the joey undergoes a profound transformation from an embryonic form to a miniature version of the adult. Key physical milestones include the development of the hind limbs, which are merely buds at birth, and the gradual growth of a soft coat of fur. The joey’s eyes will also open several months into the stay, allowing it to begin observing the world outside the pouch.
The North American Opossum, the only marsupial found north of Mexico, exhibits a significantly shorter pouch residency. Opossum joeys are typically born in large litters and remain firmly attached to a teat for about six weeks. They begin to emerge from the pouch around 55 to 70 days old, a much more accelerated timeline than their Australian counterparts.
The mother’s reproductive system is highly specialized to support this extended development. She can produce milk with different fat and protein contents simultaneously from separate teats to meet the varying nutritional needs of a newborn joey inside the pouch and an older joey suckling from the outside. This facilitates the continuous cycle of marsupial reproduction.
The Gradual Transition to Independence
The shift from full-time pouch dwelling to life outside is not an abrupt event but a gradual transition. For many macropods, the first sign is the joey beginning to poke its head out of the pouch opening. As it grows, the joey will make increasingly longer excursions from the pouch, usually starting around six months for a kangaroo.
These early ventures are short, exploratory hops, often followed by a quick retreat back to the safety and warmth of the pouch. The mother controls the opening with a sphincter muscle, and as the joey gets larger, the pouch skin stretches considerably to accommodate its growing body.
Eventually, the mother begins to discourage re-entry as the joey becomes too large and its weight makes hopping cumbersome. The final, permanent exit from the pouch typically occurs between eight and eleven months, depending on the species, but this does not signify complete independence.
The joey, now called “at foot,” continues to follow its mother closely and nurses by reaching its head back into the pouch or suckling from an elongated teat outside. This supplementary nursing period continues for several months, often until the joey is well over a year old. For example, a Red Kangaroo’s dependence may last until 12 months, while a Grey Kangaroo joey may suckle until 18 months of age. This extended nursing allows the young animal to gradually wean itself while the mother is often already supporting a new joey developing inside the pouch.