– (Tom Womb)
1. The estrous cycle (or “estrus”) of the female lasts from 22 to 42 days. Males detect this phase by smelling her urine and show off to win her over, and may even fight over her partner. When she chooses a partner (larger applicants are preferred), she puts herself in position. The male mounts her, and sex lasts between 15 and 30 minutes. Fertilization occurs in less than 48 hours
– (Tom Womb)
two. In utero, gestation lasts from 30 to 39 days. One or two days before giving birth, the female cleans the marsupium – the scientific name for the pouch. This is because, at times when there are no young living there, the female’s nipples, which are in the pouch, release a gray secretion. In preparation for giving birth, the female places her head in the pouch and licks this secretion out.
– (Tom Womb)
3. When giving birth, the female assumes a specific position, which varies with the species. Red kangaroos, for example, sit with their tail between their paws, resting on their lower back. Gray kangaroos hold their tail in a normal position, but curl up, bringing the vagina closer to the pouch. The idea is to make it easier for the pup to climb
– (Tom Womb)
4. The pup is born still in a very early embryonic state, measuring about 2 cm and weighing about 1 g. The eyes are closed and the hind legs are underdeveloped, but he has the strength in his upper limbs for his difficult mission: climbing his mother’s fur to the baby carrier. This journey takes about three minutes.
– (Tom Womb)
5. Upon reaching the pouch, the calf looks for one of the mother’s nipples, which, when grasped, dilates, attaching itself to the baby’s mouth. During the growth phase, the composition of the milk changes to meet the puppy’s needs: in the first six months, the liquid is mainly composed of carbohydrates. Then lipids (fat) become the major component. The marsupium is where the baby «ends» its development because, unlike other mammals, marsupials (the group to which the kangaroo belongs) do not have a placenta. This pouch is nothing more than a fold of skin that covers the female’s nipples and has no hair inside. Here, the pup will spend the next 200 days suckling and developing.
– (Tom Womb)
6. Despite the weight she carries, the mother goes on with life normally, being able to jump and run during the time the calf is in the pouch. After about six months, the baby slowly starts to come out of the carrier to explore – but, in that beginning, he always returns to the bag. The baby remains “living” in the baby carrier until around 8 months old (red kangaroos) or 11 months old (grey kangaroos), when it leaves for good. At this point, the red kangaroo is already 4.5 kg (20% of the mother’s weight) and barely fits there anymore. Even after becoming independent, he still usually returns to his mother to feed on her milk for six months.
Three in one
– ()
1. Due to an evolutionary adaptation against drought and lack of food, female kangaroos are able to develop up to three young at the same time in different stages.
two. While one already lives outside the pouch, but still goes to the mother to breastfeed, and another is still a newborn and is suckling inside the pouch, a third, still in embryonic form and with no more than 100 cells, called a blastocyst , lies dormant in the womb
3. When the “middle” sibling leaves the marsupium for good, the blastocyst develops again, is born after pregnancy and takes its place in the pouch. This feature is called embryonic diapause and allows you to easily replace the offspring if a pup dies.
CONSULTANCY Rafael Antunes, biologist from Uneb and professor at Colégio Integração, in Teixeira de Freitas (BA)
SOURCES Monographs on Marsupial Biology: Reproductive Physiology of Marsupials, by Hugh Tyndale-Biscoe and Marilyn Renfree, and Kangaroos: Biology of the Largest Marsupials, by Terence J. Dawson