BIRTH AND THE CLIMB TO THE POUCH
Birth is not a trivial event even though the young is so small. In fact because it is so small and fragile it is important that the mother acts to give the tiny young the best possible chance of reaching the pouch and attaching to a teat. She does this largely through pouch cleaning and birth posture. Although there was early evidence of an aided climb to the pouch by the new born joey, it was not until the observations of Geoff Sharman and John Calaby in 1964 that the process was completely described in the Red kangaroo. Our understanding of birth has been expanded by the work of Hugh Tyndale-Biscoe and Marilyn Renfree and their co-workers on the Tammar wallaby.
One of the signs that birth is approaching is the act of pouch cleaning. The pouch skin secretes a waxy compound which dries to a dark scale if the pouch has been occupied. The female kangaroo holds the pouch open with her forepaws and sticks her head well into it and licks the scale away. Cleaning begins one to two days before birth and it becomes most intensive one to two hours before birth, even though by then the pouch is already clean. Licking of the urogenital opening also increases intensity near birth.
In this intensive phase the female adopts a birth position which is characteristic to each species of kangaroo. With three Red kangaroo the tail is passed between the legs, the legs are extended forward and the pelvis is rotated forward. The mother usually supports herself with her back against the tree or shrub. Wallaroo group and antilopine adopt a similar position, except the antilopine does not appear to support the her back against a vertical object. The birth position is a little different in the Grey kangaroo, according to Bill Poole. When they squat readying for birth they do not bring their tail forward between their legs but keep it in a normal position. The pelvis is twisted forward advancing the cloaca closer to the pouch. The legs are thrust forward with the toes off the ground, the weight being taken by the heels.
Just before birth the small yellow yolk sac appears at the urogenital opening; following this come the clear allantois. Within seconds birth occurs, with the foetus still enclosed in the amnion. The newborn remains still for only ten to fifteen seconds before beginning to tear its way out of the amnion and start its climb to the pouch. The young climbs through the fur with a swimming motion using alternate forelegs. The umbilical chord breaks after about three centimetres of the climb. The time taken for the young to disappear over the edge of the pouch is about three minutes.
The mother takes no obvious active role in the process apart from ensuring that she maintains the proper position and cleans up the area. Once the newborn reaches rim of the pouch it climbs down to the nipple and attaches within a few minutes. The young at this stage has a sense of direction, i.e. up and down, that is determined by the inner ear which is advanced in its development. The sense of smell is also functional at this stage and the young appears to able to distinguish certain structures by touch. It is by these means that it is able to rapidly find and attach itself to the nipple.