Kangaroo Reproduction Kangaroo Reproductive System

Photo: Kangaroo female with baby in pouch and male

Kangaroos have unusual genitalia and reproductive systems. They have a single opening, called a cloaca, for intestinal, urinary, and genital tracts (see photo). This single opening is similar to that seen in reptiles and birds. The female kangaroo also has three vaginas, two uteruses and carries her baby in a pouch on her abdomen. Kangaroos share this unusual sexual anatomy with other marsupials. But, contrary to myth, the male kangaroo has a single pointed penis.

A kangaroo baby, called a joey, is born in a very early stage of development. It crawls out of its mother's cloaca and into her pouch where it grows into a viable offspring.

Male Kangaroo Reproduction Kangaroo's Penis & Scrotum (Balls)

The male kangaroo has a slender tapering penis located behind its scrotum. This arrangement is different from male placental mammals that have their penis in front of the scrotum.

When aroused, the male kangaroo’s erect penis protrudes out of its cloaca and curves forward and upwards. At other times, its flaccid penis is retracted and safely tucked away into a preputial sac inside its cloaca.

The male kangaroo has a fur-covered pendulous scrotum that is retraced tightly against its body when hopping or engaging in coitus. That is to say, its balls usually dangle under its body but are pulled up against its body when hopping or having sex. This adaptation of a dangling scrotum is vital for keeping the animal’s testicles, inside the scrotum, at a temperature of 2–5 degrees cooler than its core body temperature. The male kangaroo also has another adaptation to Australia’s harsh environment. Its body shuts down sperm production during periods of severe drought to conserve energy.

Contrary to another myth, kangaroos don't play with their balls. However, in extremely hot weather, the male kangaroo licks them to keep them cool.

The male kangaroo does not have nipples or a pouch. The male kangaroo reaches sexual maturity at approximately 24 months.

Female Kangaroo Reproduction Kangaroo's 3 Vaginas & 2 Uteruses

Photo: Female kangaroo with baby joey

The female kangaroo has three vaginas and two uteruses. The two outermost vaginas are used for sperm transportation to its two uteruses. Babies are born through the middle vagina. (See diagram). By contrast, female placental mammals have only one uterus and one vagina.

With this unusual reproductive system, a female kangaroo can be continuously pregnant, with a fertilised egg in one uterus waiting to be released, a baby growing in the other uterus, one in her pouch and another hopping outside but coming to its mother for milk. In this way, a female kangaroo can take care of multiple joeys at different stages of development. Another unique feature of these animals is that the female kangaroo can practice birth control during drought and starvation by putting the babies growing in her uteruses 'on hold', stopping their future development until conditions improve. This is called embryonic diapause. Then, when the mother's pouch becomes free, the next baby will be born and move into the pouch, and the fertilised egg "on hold" in a uterus will start developing into a new foetus. Because of this multiple-offspring strategy and other adaptabilities unique to the kangaroo, populations can increase rapidly when food is plentiful.

The reasons why kangaroos have three vaginas and two uteruses is not fully understood. It may be a biological anachronism. Or it is because having babies in different stages of development gives these animals a reproductive advantage by allowing them to procreate rapidly in good times.

The female kangaroo reaches sexual maturity at around 16 months.

Kangaroo Pouch Inside a Kangaroo's Pouch

The female kangaroo's pouch is located on the front of her body. Because baby kangaroos are born underdeveloped, its mother's pouch acts as an external womb and provides a young kangaroo with food, warmth, shelter and protection as it grows.

A kangaroo's pouch has a horizontal opening on top and is lined with muscles and ligaments that allow it to expand to accommodate the growing joey inside. The inside of a kangaroo's pouch is warm, nearly fur-less, and has four nipples that supply milk with different nutrient levels. In addition, the pouch is lined with sweat glands that release antimicrobial fluid to protect the joey from germs, viruses and parasites.

The female kangaroo is not born with a pouch. Instead, her pouch develops as she begins to reach sexual maturity.

Kangaroo Sex How do Kangaroos Mate?

Kangaroos have no fixed breeding period. However, they will have sex more often when food is plentiful and not so during periods when food is scarce. Females usually have one young per year during the months of October to March (late spring to early autumn in Australia).

When the female is sexually in heat, she will exhibit a particular behaviour signalling that she is receptive. An interested male will sniff her urine and approach her. It is common for a dominant male to drive off lesser rivals for mating rights. When a male wants to establish mating rights, he will stand on his toes and tail tip and make growling and clucking noises. This signals to others that he is willing to fight for the right to mate. If challenged, a fight will ensure. Kangaroo fights rarely result in serious serious injury. The successful male will then approach the female, and if she is receptive to him, he will copulate with her. Copulation sessions can last up to 50 minutes. After copulation, the male will move on to another female.

Kangaroo Egg Do Kangaroos Lay Egg?

Kangaroos do not lay eggs. But kangaroos do produce eggs encased in a very fine and fragile shell similar to that of birds and reptiles. This egg is about 0.12 mm in diameter with a shell just a few microns thick. This shell disintegrates, leaving only the amnion when the egg reaches the third gestation phase.

The gestation period for a kangaroo is approximately 30-36 days and varies amongst the different types of kangaroos. Females give birth to one offspring. Twin births have been reported, but only one baby survives.

Kangaroo Birth How a Kangaroo Baby is Born

As the time approaches for the young kangaroo to be born, the female kangaroo cleans out its pouch by sticking her head into it and licking the inside clean. It then takes up a "birthing position" by sitting on its back with its tail between its legs and the hind legs extended straight forward. It also leans the trunk of its body forward. It then licks its cloaca, possibly to stimulate the birth. It also licks its fur from its cloaca to the pouch opening, possibly as a path for the young joey to follow. During birth, the young kangaroo breaks out of the amnion with its small, sharp claws, and emerges from the birth canal.

Kangaroo Baby A Kangaroo Baby is Called a Joey

The newborn kangaroo is called a joey and is no larger than a jelly-bean (2 cm or 0.79in). It weighs less than one gram (0.035oz). It is born blind, hairless, with stumpy forelimb and hardly any trace of its hind legs. Even though it is still very underdeveloped, the young newborn has an excellent sense of direction, knowing which way is up and down and an acute sense of smell. Using its tiny forelimbs in a swimming motion, the young joey crawls laboriously up its mother's fur to the pouch. This journey takes about three minutes. The joey's journey is made entirely by itself. The mother does not assist it in any way. Once inside its mother's pouch, the joey quickly attaches itself firmly to one of four nipples in the pouch.

Once it has attached itself to its mother's nipple, the young joey will stay hidden for up to six and a half months. Then it will start to tentatively pop its head out of its mother's pouch and observe the world around it. About two weeks later, it will have gained enough confidence to venture out of the pouch and hop about close to its mother. However, if frightened, it will immediately jump back into the safety of the pouch. By the time it is about eight months old, the joey no longer uses its mother's pouch.

Kangaroo Milk Production Two Types of Milk

The female kangaroo can produce two types of milk, depending on the joey it is feeding. The milk produced in the nipple on which an embryonic joey is attached will be different from the milk produced to feed a joey that has already left the pouch and only comes back to be weaned.

Did Baby Kangaroos Bud from their Mother's Nipples?

Because the young joey attaches itself so firmly onto its mother's nipple and is very difficult to pull away from it, early European explorers thought that baby kangaroos just miraculously grew off the nipple in the mother's pouch. This is because they couldn't see any opening inside the pouch from which the joey could have emerged. They didn't know about the little joey's perilous journey from the birthing canal to the pouch.