Kangaroos are mammals, a category of animals frequently associated with reproduction queries. Did you know not all mammals give birth? Contrary to popular belief, some mammals lay eggs!

Are those egg-laying mammals actually kangaroos? Do kangaroos lay eggs?

No, kangaroos do not lay eggs. Although there are mammals that do lay eggs, marsupials (in which kangaroos are included) do not. Instead of laying eggs, pregnant kangaroo females give birth to small joeys and nurse them inside a pouch for about six months.

Do Kangaroos Lay Eggs?

Due to their unique reproduction, people are often uncertain how do kangaroos actually give birth to babies. Kangaroos are marsupial mammals, and they belong to the group of animals that give birth to live young.

The only egg-laying mammals are monotremes mammals, including the platypus and echidnas. Besides them, birds, fish, lizards, and reptiles as well hatch from eggs.

However, female kangaroos have one physical characteristic that sets them apart from most animals. Pouches.

How do joeys end up in pouches, and how does the kangaroo reproduction actually works? Let’s find out.

Kangaroos are Mammals

Mammals are a group of vertebrate animals characterized by feeding their young with milk, secreted from the mother’s mammary glands. Not only that, but mammals also share other characteristics.

They are warm-blooded, like several other vertebrates. Except for some marine mammals, most mammals have fur. Regardless of being aquatic or terrestrial, mammals use their lungs to breathe.

Mammals can be sorted into three subcategories: placental, marsupial, and monotremes.

• Placental mammals gestate their young inside a uterus. There, the young animal is nourished by the placental tissue through an umbilical cord. Most mammals are placental, humans included.
• Marsupial mammals also start their development inside the mother’s uterus. This uterus also provides a placenta, which is functionally different from placental mammals. The young are born at an early stage of development. For this reason, babies are kept inside a pouch or a skin fold on the mother’s body. This pouch is called marsupium and contains nipples through which she feeds milk to the baby.
• Monotreme mammals are the least common type of mammals and reproduce by laying eggs. Another significant difference between monotremes and other mammals is that milk is fed to the young through the skin instead of a nipple.

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How do Kangaroos Give Birth

Reproductive strategy

Kangaroos are opportunistic breeders and can reproduce year-round if conditions are suitable.

Their reproductive style is highly adapted to environmental uncertainty, relying on different strategies to overcome drought periods.

However, kangaroos tend to reproduce after drought-breaking rain, when vegetation becomes lush and abundant.

Gestation

Once the Egg cell is fertilized it takes 28 – 34 days of gestation to be ready for birth. However, kangaroos have a unique capability to suspend pregnancies, called embryonic diapause.

This allows a mother to delay pregnancy if she is still nursing a joey (baby kangaroo), keeping the small embryo in the uterus for many months if needed.

This unusual feature is also why female kangaroos have 2 uteri and 3 vaginas, united to a common connection where excretion also occurs.

Birth

At the time of birth, the joey is still very small and embryo-like. Compared to placental mammals, kangaroos have short gestational periods and are born very small, weighing approximately 1g.

It then crawls out of the birth canal, following a saliva trail made by his mother through her fur, until he enters the pouch.

Only one joey is born at a time, although there are rare reports of two simultaneous babies.

Development in the pouch

Only female kangaroos have pouches as they are the ones that nurse the babies. The stretchy pouch is not just a simple as a pocket. It confers the joey all it needs to grow until it is a fully developed juvenile.

Inside the pouch, 4 nipples supply milk. Milk is a baby superfood as it contains not only all the necessary nutrients and water but also antibodies that support the joey’s immunity system. As the baby grows, the nutritional content of the milk changes to better suit its needs.

Through the 4 different nipples, the mother can supply different types of milk, each independently adequate to a particular life stage. This means that she can simultaneously supply two types of milk to joeys of different ages.

The inside of the pouch is hairless and contains sweat glands that release antimicrobial molecules. These help to protect the babies from potential infections.

The gestation phases vary between Kangaroo species, but generally follow the following timeline:

• 3 months: start to grow fur
• 5 months: pokes his head out of the pouch
• 6 months: starts exploring outside the pouch, returning to it afterward
• 8 to 11 months: permanently leaves the pouch but continues to suckle for a few more months

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FAQ on Kangaroo Reproduction

How long do joeys stay in the pouch?

Joeys will stay inside a mother’s pouch for at least 6 months. During that period of time, joeys grow fur, ears, limbs, and other body parts necessary for independent living. However, young joeys will find safety in their mother pouches whenever threatened or scared for a few more months until becoming completely independent.

Can kangaroos have twins?

There are reported cases of birth of kangaroo twins, but these occasions are extremely rare. However, when this happens, usually, the stronger baby gets spared by the mother. It is very unlikely that both joeys would survive in the wild, so the mother has to pick between the two. Although kangaroos can have three joeys at the same time, yet, they cannot be in the same development phase.

Do kangaroos throw their babies?

Yes, kangaroos will throw their babies in order to save themselves when cornered by predators. However, sacrificing babies does not only happen because of its own safety. In case a mother kangaroo has multiple babies in different stages, the mother would sacrifice one baby to increase the chance of survival for the other babies when lacking nursing resources.

Final Thoughts

Kangaroos do not lay eggs because they are marsupial mammals that give birth to live young. Kangaroos usually give birth to one baby that stays in their pouch for at least 6 months, considering that the baby is born very undeveloped.

References
https://www.businessinsider.com/whats-inside-kangaroos-pouch-joey-baby-animals-2019-8
https://www.discoverwildlife.com/animal-facts/mammals/how-long-do-joeys-stay-in-the-pouch/
https://ielc.libguides.com/sdzg/factsheets/redkangaroo/reproduction
https://kangaroocreekfarm.com/about-roos/
https://babbyfarms.net/blog/the-kangaroo-birthing-cycle/
https://pubmed.ncbi.nlm.nih.gov/20079531/