Although many marsupials raise their young in pouches – including possums, Tasmanian devils, and even koalas – Kangaroos are almost certainly the most iconic.
So what’s it like in a kangaroo’s pouch?
Think of the kangaroo’s pouch as an upside down hoodie sweatshirt, said Rick Schwartz, a zoo keeper and national spokesman at the San Diego Zoo. The hood of the sweatshirt is the pouch, and the drawstrings are the mother’s muscles that open and close it. “It pretty much opens up when she wants it,” Schwartz told Live Science.
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The inside of the pouch has the texture of the kangaroo’s skin but is hairless. It’s soft and similar to the skin on the inside of a person’s wrist, Schwartz said. The inside of the bag is very warm, just like the mother’s body temperature: around 40.5 degrees Celsius. Because of this, it can sweat in there.
The pouch contains four teats or milk ducts. If a mother kangaroo gives birth to a joey through the vaginal canal after 32 or 33 days of pregnancy, her baby is extremely undeveloped. About the size of a gum bean and weighing less than a gram, the newborn Joey crawls with his front legs into his mother’s pouch. There it snaps into place on an elongated teat that swells and pokes into the baby’s throat and holds it in place for about three and a half to four months, Schwartz said.
The joey stays in the pouch for about four and a half to five months before surfacing, and then it starts exploring, always staying close to its mother before returning to its pouch, Schwartz said. Over the next few months the joey will start to explore further afield and for longer periods of time and at around 8 months it will get really adventurous. The joey will wean itself between 10 and 12 months and then will not hop back into the pouch.
Since the joey spends months in the pouch before surfacing, it empties inside. Later in development because it comes and goes to explore, the Joey Dirt haunts, Schwartz said. This means that the kangaroo mom has to do something around the house. To clean the bag, she sticks her whole head in to scrape out the dirt and droppings with her tongue, either working around a young Joey or kicking an older one out while she works.
Kangaroos only give birth to one joey at a time. But when they mate, when the conditions are not right for raising a baby – for example during a drought – the animal’s body will hold back the embryo from implanting in the uterus. Then, when the time is right, the embryo comes out of dormancy and the mother begins pregnancy, Schwartz said.
The female kangaroo can give birth to up to four cubs from just one mating in a year or more, he added. She can give birth to a joey, then her body delays implanting the next embryo until the first joey is a few months old and spends time out of the bag. “Your body can make the right milk nutrients for an 8 month old baby and the other teat can make the right nutrients for a newborn,” he said.
Originally published on Live Science.