January 07, 2004

Making Kang A Roo


From about 190 days the red kangaroo young, which now weighs about 2 kilograms, begins to leave to leave the pouch. This is a much shorter time than in the grey kangaroos, which make take almost 100 days more. The young kangaroo first leaves the pouch in the typical way of macropodines: it falls out. However the mother plays an active part in these events. She has control over the numerous muscles that control pouch size and opening. The entrance to the pouch has a semicircle of muscles on each side and when these are contracted the entrance is closed and the pouch is pulled up tight against the body so that the young is retained if the mother is alert or alarmed. Alternatively, the mother can really relax the pouch and its opening and let the joey fall out; she can also actively tip the joey out by tipping the pouch.

Early excursions from the pouch are brief. they usually occur when the mother is cleaning a relaxed pouch or is just lying relaxed. The young then may fall or ooze out. In such circumstances the joey may also be partly out and not have to worry much about climbing back in if the relaxed pouch is agape. Also, the young may fall by overbalancing: it simply stretches to far out while exploring the world or trying to pick at some grass. This usually is the only way the joey leaves the pouch in the two or three weeks after initial vacation. Later in pouch life the young is sometimes deliberately tipped out by its mother, usually when she is cleaning the pouch. As the joeys grow they start to get out more often by their own efforts; they dive out if the mother is standing or just climb out if she is lying down.

The 'in-out' period from the first emergence to the permanent emergence is a period of life that placentals do not have. Kangaroos have the benefit of a good look at the world before having to face it permanently. During this period the mother still carries out pouch cleaning and grooming the joey, initially in, but later outside, the pouch. In addition, the mother's behaviour develops in relation to controlling the young when it leaves the pouch and also when it returns. She has general surveillance of the young and helps in its learning as it approaches permanent exit.

On the young's first exits from the pouch it stands clumsily where it has fallen from the pouch for less than a minute and then gets straight back into the pouch. In the first few weeks after the initial pouch emergence may make frequent short excursions, which usually last no more than a couple of minutes and are rarely more than one or two metres from the mother. After these brave excursions the young returns the young returns to its mother and put its head into the pouch. It may stand in this position and be groomed by the mother or it may get into the pouch by kicking off with its hind legs. The young does a complete somersault and ends up facing the pouch opening. For a big young this procedure is a major effort there is much activity before comfort is reached; a bit of the tail or leg still protrudes.

For the young to get into the pouch the mother has to cooperate in a synchronised manner. As the young puts its head into the pouch and kicks off, the mother bends forward so that the pouch opening is brought closer to the ground. For small young the mother bends lower. The movement of the mother is crucial, since if she does not cooperate the young is left with its head and forelimbs in the pouch, kicking with its hind legs but unable to get over the lip of the pouch.

Return to the pouch is initiated by the young but sometimes the mother does not want to cooperate, notably is she lying down resting. Then a bit of pestering is needed to get her to stand. The young sniffs at the pouch and scratches around the opening with its forepaws, trying to get its head in the pouch. It may even sniff and push at the mother's head. She may respond or not. The young also spends on long periods at this stage simply standing with its head in the pouch. This too requires cooperation. Apparently much of this behaviour is 'comfort' because suckling does not take place.

Late in the pouch life the mother has a variety of ways of preventing or discouraging the joey from entering the pouch. She may simply move away when the young tries to put its head inside. She may, more or less gently, push the young away or fail to cooperate by standing up if she was lying down. However, if something disturbs the mother she stand up quickly and calls and the young can be in the pouch in a couple of seconds.

In the final week before permanent exit the mother moves away from the young frequently but then stops and allows the young to catch up. The mother is training the young to readily recognise her and follow when she move off. By the time the permanent pouch emergence occurs the young has also learned that it will not be allowed back into the pouch unless there is some alarm. Finally the mother prevents the young from getting in and after a couple of days it stops trying.

Posted by Madfish Willie at January 7, 2004 12:58 AM | TrackBack
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