Kangaroos do not lay eggs. This Australian marsupial gives birth to live, but extremely undeveloped, young. The confusion often arises because of the three distinct groups within the class Mammalia: Placental Mammals, Marsupials, and Monotremes.
The Simple Answer: Mammals vs. Egg-Layers
Placental Mammals, such as humans and dogs, carry their young in the uterus for a long gestation, nourishing them via a placenta. Kangaroos are Marsupials, characterized by a short internal gestation followed by a long period of development outside the womb, typically in a pouch.
The only mammals that lay eggs are Monotremes, a small group consisting solely of the platypus and the echidna. Kangaroos are not oviparous and are biologically distinct from these egg-laying mammals.
The Unique Marsupial Birth Process
The kangaroo’s reproductive strategy involves an exceptionally short gestation period inside the mother’s uterus, lasting only about 33 days for many species. After this brief time, the mother gives birth to an embryo-like offspring called a joey.
The newborn joey is incredibly small, often compared to the size of a jelly bean. This tiny creature is hairless, blind, and its hind legs are undeveloped. However, its forelimbs are surprisingly well-developed and muscular, which are essential for its survival.
Immediately after birth, the joey begins an instinctive climb from the birth canal to the opening of the pouch. This arduous journey is performed entirely by the tiny joey using its forelimbs and sharp claws. Once the joey arrives at the marsupium, it fastens onto one of the mother’s four teats, where it will remain firmly attached for months to complete its development.
Life and Development in the Pouch
Once secured inside the pouch, the joey enters a specialized environment for its lengthy period of post-natal growth. The pouch provides a secure and warm space, with the temperature carefully maintained by the mother. The joey remains permanently attached to the teat for the first two to three months, receiving constant nourishment.
A remarkable aspect of kangaroo biology is the mother’s ability to produce different types of milk simultaneously. If she is nursing both a small, newly attached joey and an older joey that periodically leaves the pouch, she provides two distinct milk compositions. The milk for the younger joey is typically high in protein and carbohydrates, while the milk for the older, more developed joey is significantly higher in fat to support its rapid growth.
The joey will start to poke its head out of the pouch at around six months of age. It begins to make short exploratory trips out of the pouch to graze and build strength. The joey typically leaves the pouch for good at about eight months but may continue to suckle from the mother for several more months.