Kangaroo Reproduction Male & Female Kangaroo Sexual Anatomy

Kangaroos have some unusual sexual and reproductive characteristics. The male has a two-pronged penis. The female kangaroo has three vaginas and two uteruses, and she carries her young in a pouch.

Also, these animals don't have a separate opening for urine and faeces (pee and poop). Instead, both male and female kangaroos have a modified cloaca with a single opening through which they pass urine and faeces. Their sexual organs also share the same opening.

• What is a Kangaroo?

Kangaroo Penis

The male kangaroo's penis has two-prongs (bifurcated) and is located behind its scrotum, and inside its cloaca. This is different from most other male mammals that have a penis located separately in front of the scrotum, either exposed like a human or in a sheath like a dog or a cat. Unlike placental mammals that have a dual purpose penis to urinate and inseminate, a kangaroo's penis serves only one purpose—to transport sperm to inseminate the female. It does not urinate through its penis.

When flaccid, the kangaroo's penis is retracted, and safely tucked away inside its cloacae. When aroused, its erect penis protrudes out of its cloacae and curves forward and upwards. The kangaroo’s two-pronged penis structure enables the male to inseminate the two vaginas of the female kangaroo.

Kangaroo Scrotum

The kangaroo has a pendulous scrotum lightly covered with fur that is retraced tightly against its body when hopping or engaging in coitus. That is to say, it dangles from beneath the animal and is pulled up against its body when required. This adaptation of a dangling scrotum is vital for keeping the animal's testes inside the scrotum at a temperature of 2–5 degrees cooler than its core body temperature. In extremely hot weather, the male kangaroo licks its scrotum to keep it cool.

The male kangaroo also has another adaptation for Australia's harsh environment. Its body shuts down sperm production during periods of severe drought to conserve energy.

Female Kangaroo Reproductive Anatomy Three Vaginas and two Uteruses

Kangaroo Vagina & Uterus

As with all marsupials, the female kangaroo has three vaginas and two uteruses (uteri). The two outermost vaginas are used for sperm transportation to the two uteruses. Babies are born through the middle one. (See photo). 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 during times of drought and starvation, the female kangaroo can practice birth control by putting the babies growing in her uteruses 'on hold', stopping their future development until conditions improve. This is called embryonic diapause. 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.

Kangaroo Pouch

The female kangaroo has an external pouch on her abdomen in which it carries a baby. She isn't born with a pouch, but instead, her pouch grows as she starts to reach sexual maturity. (Note: The male kangaroo does not have a pouch).

The kangaroo's pouch is located on the front of her body. It has a horizontal opening that can be drawn shut by powerful muscles when required. Like the womb in other mammals, the kangaroo's pouch is lined with muscles and ligaments that allow the pouch to expand to accommodate the growing joey inside.

The inside of the pouch is warm, nearly fur-less, with four teats that supply milk with different levels of nutrient. Because kangaroo babies are born extremely underdeveloped, her pouch acts as a second womb to grow to a viable offspring.

Kangaroo Mating How Kangaroos Mate

The male kangaroo reaches sexual maturity at approximately 24 months, and the female at around 16 months. They have no fixed breeding period but will mate more often when food is plentiful than during periods when food is scarce.

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.

Kangaroos fight by kicking each other with their powerful hind legs and by attempting to scratch their opponent with their sharp claws until the vanquished is driven off. They rarely seriously injure each other.

The male will then approach the female, and if she is receptive to him, he will copulate with her. After copulation, the male will move on to another female.

Kangaroo Egg The Kangaroo's Unusual Egg

The kangaroo egg, which is about 0.12 mm in diameter, descends from the female's ovary into a uterus where it is fertilized. Once fertilised the egg is encased in a very thin shell similar to that of birds and reptiles. This shell is just a few microns thick and disintegrates when the egg reaches the third phase of gestation. A remnant from the evolutionary past, this unusual characteristic is common amongst marsupial mammals.

The gestation period for a kangaroo is approximately 30-36 days and varies amongst the different types of kangaroos.

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 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 lick its fur from its cloaca to the pouch opening, possibly as a path for the young joey to follow.

The young kangaroo, no larger than a jelly-bean (2 cm), and weighing less than one gram, soon emerges from the birth canal. It is born blind, hairless, with stumpy forelimb and hardly any trace of its hind legs. Even though it is still so underdeveloped, the young newborn has an excellent sense of direction, knowing which way is up and down and also 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 it 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

Photo: Kangaroo mother with joey

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.