When it comes to mom, baby joeys are extra clingy. They’ll spend months in the comfort of mama's pouch but getting there isn’t as easy as it seems.
A kangaroo mom with a little babe tucked safely into her pouch is a familiar symbol of motherhood in the animal kingdom. But, the thing is, newborn joeys don’t look much like kangaroos at all. They actually look more like this - a teeny squishy naked blob. And that’s because they are born at a VERY early stage of development - akin to a human fetus at a mere 10 weeks.
Metatherians are part of a mammalian group endemic to Australia that also includes wallabies, koalas and wombats. This class of females comes equipped with a pouch that acts an incubator - and the tiny newborns make an extraordinary journey to reach it. Just before a kangaroo delivers her baby, she will lick a pathway from her genital opening to her pouch, preparing her little one for an epic climb into to its new home. The saliva creates a damp, clean road full of pheromonal cues for the joey to follow. Despite being underdeveloped in many ways, a newborn kangaroo has a strong olfactory system which keep joey on right path.
Once inside the pouch, the joey latches onto a teat and doesn’t let go for another several months as it continues to develop. The first milk that the joey receives is very dilute, it’s more like water with a few added sugars. The newborn’s digestive system is not yet able to take on complex fat or protein molecules - so richer milk doesn’t start to flow until about three months later. Along with milk, they joey also relies on mom’s body heat for warmth. For the first couple months, joeys are ectothermic, meaning they cannot regulate their own temperature. Joeys are also born without fully functional lungs, so direct transfer of oxygen happens through skin-on-skin contact. After the first few months, the composition of mom’s milk changes to include more fat and protein, but it also contains molecules that facilitate further development of her baby’s immune system. Female kangaroos have four teats that can provide uniquely crafted milk, catering to the developmental and nutritional needs of their newborns and any older roos that are still feeding. As you can imagine, with little joey feeding for many months at a time, it can get kind of gross in the pouch. But as most moms know all too well, getting down and dirty is just part of the job. Come cleaning time, she will stick her snout into the pouch and lick up the mess. Oh the things we do for our babies!
After about six months, the joey is typically ready to begin exploring the outside world. but don’t stray too far from their safe and cozy home. Roos will come back to the pouch for pretty much as long as they can fit into it. So after about nine months, it’s time for mom to say those famous last words - “Time to move out, joey.”
To learn more about the wild world of motherhood, get yourself a copy of the book, "Wild Moms" by Dr. Carin Bondar!