Kangaroos are marsupials, and their reproductive process is distinct from that of most other mammals. Unlike placental mammals where offspring develop extensively inside the mother, kangaroos give birth to highly undeveloped young. This unique birthing strategy involves a remarkable journey for the newborn, leading to a prolonged period of development within the mother’s pouch.
The Tiny Newborn Joey
A newborn kangaroo, known as a joey, is astonishingly small at birth, a stark contrast to its large parents. After a gestation period of about one month, the joey is born measuring around 2 to 2.5 centimeters (about 1 inch) in length. Its weight is less than a single gram, often compared to the size of a jelly bean or a bumblebee.
At this stage, the joey is pink, hairless, and blind, resembling a tiny red worm. Its hind limbs are stumpy and not yet functional for locomotion. Despite its prematurity, the newborn joey possesses strong forelimbs. These forelimbs are crucial for its survival, enabling it to undertake its journey.
The Journey to the Pouch
Immediately after birth, the tiny, blind joey embarks on a perilous climb to its mother’s pouch. The mother kangaroo does not assist this journey; the joey must instinctively crawl from the birth canal, located near her tail, up through her fur. To facilitate this trek, the mother often licks a pathway through her fur, creating a moist, scented trail that guides the joey.
The joey uses its strong forelimbs in a swimming motion, gripping the mother’s fur with its claws to pull itself upwards. Its sense of smell is essential for navigating this critical distance to locate the pouch opening. This journey, despite its arduous nature, is completed within minutes, highlighting the joey’s innate drive for survival. Any misstep during this trek can be fatal for the newborn.
Growth and Development in the Pouch
Upon reaching the safety of the pouch, the joey latches onto one of its mother’s teats, which then swells inside its mouth, securely attaching the joey for continuous nourishment. The mother kangaroo produces specialized milk, with its composition changing to match the joey’s developmental needs. Initially, the milk is high in carbohydrates and water, providing hydration and energy, along with antibodies for immune system development. As the joey grows, the milk becomes richer in protein and fat, supporting muscle development and overall growth.
The joey undergoes rapid growth and significant physical changes inside the warm, protective pouch, which maintains a temperature similar to the mother’s body. Over several months, it develops fur, its eyes open, and its hind limbs strengthen. Pouch life varies by species, ranging from about six to eight months for red kangaroos and up to 11 months for grey kangaroos. Joeys gradually begin to peek out, then emerge for exploratory trips, gaining independence while still returning to the pouch for feeding and security. Even after leaving the pouch, joeys may continue to suckle for several months, sometimes up to a year or more.