Walking around with a pocket attached to your stomach opens up a world of opportunities for smuggling contraband in the form of candy and cola into a movie theatre, but a kangaroo pouch carries out a much more important role than simply acting as hands-free luggage.
What is a joey kangaroo?
Before we get to the function of the kangaroo pouch, it’s worth touching on the somewhat bizarre reproductive anatomy of kangaroos. Female kangaroos have three vaginas that share an opening but divide into three and then meet back at the uteruses (of which there are two). A kangaroo joey will travel down the central vagina while the sperm reaches the uteruses by using the vaginas on either side. This unusual structure is complemented by the males’ penis shape which is often two-pronged, one for each of the sperm-facilitating vaginas. These adaptations actually mean that the female can be perpetually pregnant, with a kangaroo pouch and two uteruses in which to house developing joeys.
What does the inside of a kangaroo pouch look like?
Once an egg has become fertilized inside one of the two uteruses, it’s just one month before the kangaroo joey is ready to be born, and things only get weirder from here. When the baby emerges, it’s about the size of a jellybean, which set against the canvas of its mother’s 40-kilogram (88 pounds) body looks completely ridiculous.
The baby, now on its mother's fur, uses its tiny forearms to drag itself up the body and into the pouch. The harrowing journey takes several minutes and once the exhausted joey is inside, it latches on to one of four teats inside the pouch.
Inside the pouch, it's essentially a hairless warm (and slightly sweaty) pocket that's lined with soft skin and four teats that secrete milk for the joey. The skin of the pouch also secretes antimicrobial substances that lessen the risk of infection for the developing young inside. Clever kangaroo pouch.
When does the kangaroo joey leave the pouch?
The distance from the cloaca of the female to its pouch is a matter of centimeters, but for a tiny jelly bean roo it’s an epic journey. It’s perhaps understandable then that once inside the kangaroo pouch the baby will kick back and relax, filling up routinely on its mother’s milk. Here the baby will stay until it’s developed enough to stand on its own two feet, returning to the kangaroo pouch when it needs to feed or take a nap. How long this takes depends on the kangaroo species. For red kangaroos it’s around eight months while still suckling inside the kangaroo pouch, gaining full independence around three to four months later. Grey kangaroos don’t step out of the kangaroo pouch until they are 11 months old and will continue suckling inside until they are as old as 18 months.
KANGAROO Claws, Tails, and other weapons
Adult kangaroos exhibit sexual dimorphism so the males will grow taller than the females and only the latter will have the characteristic kangaroo pouch. The males are aggressive and will fight other males when competing for a mate. They can get quite aggressive with prospective partners too. A viral photo showing a male “grieving” over its mate in 2016 was found to capture a far more sinister moment as experts predicted it may have played a role in the mate's demise.
Male kangaroos can grow to be extremely strong, growing shoulder muscles to put humans to shame, which they will use to put enemies into headlocks.
As well as using their oppressively strong arms, kangaroos are known to fight with their feet using an enormous claw that fuses the two middle toes together to disembowel their foes. The four fingers on their hands don't look much friendlier, either.
Research has also proven that their tails are capable of far more than acting as a support, as it was revealed kangaroos can use it as a fifth leg to project them forwards as they hop. They will even lean back entirely on their tail sometimes, adopting a posture that's as ridiculous as it is impressive.
Are kangaroos smart?
Unlike some humans, kangaroos don’t trade in brains for brawn as they're known to be intelligent animals with complex social groups. A recent piece of research discovered they’re even capable of communicating with humans despite not being domesticated animals. The paper, published in the journal Biology Letters, reveals how kangaroos can use their gaze to "point", and gazed intently at a human as a means of “asking” for help when struggling to get inside a sealed plastic container of food.
“Their gaze was pretty intense,” said co-author Dr Alexandra Green of the University of Sydney, in a statement. “We’ve previously thought only domesticated animals try to ask for help with a problem. But kangaroos do it too. If they can’t open the box, they look at the human and back to the container. Some of them used their nose to nudge the human and some approached the human and started scratching at him asking for assistance.”
While the kangaroos used in the study were captive animals from zoos in Australia, this doesn’t class them as a domestic animal. They needed to be used as wild kangaroos would be too spooked by the presence of humans to be interested in some food in a bag. For an animal to be classed as domesticated it needs to have been selectively bred over generations to live alongside humans.
The research offers yet another fascinating insight into the lives of these bizarre marsupials. From the mysterious kangaroo pouch to pentapedal locomotion, natural selection sure had fun with these guys.