Birth of the Red Kangaroo (1965) - Part 2 of 3

Uploaded by CSIROpublishing on 05.08.2009

Birth is preceded by the appearance of fluid from the ruptured yolk sack
and just before the young is born the female
vigorously licks the urogenital opening.
If you watch carefully you will be able to see one of the embryonic
membranes, the allantois sac fall to the ground just as the animal moves.
Now, the young is born, enclosed in
another embryonic membrane, the amnion
and quickly moves itself into a position where
it’s head is towards the pouch opening.
The young may be released from the
amnion by the mothers licking or by the
use of the sharp claws which are present on the front limbs at birth.
During the early part of its climb to the pouch
the young is attached by umbilical cord to the yolk sack,
eventually this cord is broken, sometimes
by the licking action of the female
and the young is attached only by its grip on the fur.
The time taken for the young to reach the
pouch is about three minutes - ranging from one and
a half minutes to about four and a half minutes.
During birth and the journey to the pouch the young seems to be ignored by
the female who concentrates on licking blood and birth fluids from the fur.
The female does not lick a track for the young to follow,
but licks mainly behind the young removing all traces of its passage.
After the young has reached the pouch the female
remains in the birth position licking the fur.
Fluid will continue to ooze from the urogenital opening for up to
40-mins after birth and all of it is carefully licked up by the female.
In the film we’ve just seen it was difficult to observe the moment
of birth because of the movement of the
female as she continually licked the fur.
So to see this more closely it is necessary to anaesthetise a
female with Nembutal a few minutes before the young is born.
This female is anaesthetised, again, a few millilitres
of fluid from the ruptured yolk sack appear just before birth.
The young is born head first enclosed in an embryonic membrane, the amnion.
Once released from this membrane the young starts
to make its way over the fur to the pouch.
The young, at birth, and for some time after is
attached to the yolk sack by the umbilical cord.
This cord stretches and eventually breaks
as the young makes its way to the pouch.
Sometimes the cord is broken by the licking of the female, but with
this anaesthetised animal the cord had to be broken artificially.
The umbilical cord is attached to the yolk
sack which is still in the birth canal.
The newborn red kangaroo, as with the newborn of other marsupials,
is entirely without fur. It is blind and
lacks even the development of organs
giving a sense of balance.
However, those centres of the brain concerned in
the sense of smell are well developed and the nostrils are open and large.
During its climb to the pouch only the front limbs are used since the hind
limbs which become so large later in life are mere buds at this stage.
The fur below the pouch lies in such a way that the ends
of the hairs point towards the mid-line
so that the young kangaroo crawls in the general direction of
the ends of the hairs over the fur rather than through it.
Now the young has reached the edge of the pouch
after its remarkable journey over the fur.
Once inside it will stay there for about six months
before it starts to leave the pouch for short periods.
As the young crawls down into the pouch, notice the lack
of development in the hind limbs and that they are not
being used for locomotion at all.
On this female the pouch is being held open so that the young can be filmed.
With the pouch held open like this it’s unlikely that the
young will attach to a teat because it seems to need
the ventral wall of the pouch as support while drawing
the teat into its circular and terminal mouth opening.
Later it finds an attaches itself to one of the four teats,
its tongue is large and muscular and capable of a suction pump like action.
This sucking stimulus on the teat causes the release
of clear fluid on which the newborn young lives.
As it grows this fluid will become more like the usual milk of mammals.
Once it has attached the young maintains a strong grip on
the teat which forms a pulpous swelling inside the mouth.
It is because of this that many people
have been led to believe that the young
kangaroo was born on the teat, presumably
by some process of buddying off.
However, the young can be removed from the teat
provided that it is less than one day old.
If it is any older than this it will probably be
unable to draw the teat into its mouth again.
Newborn young removed from a teat can be
placed on another teat in the same pouch.
The sucking stimulus will cause the release of fluid from the new teat.
The newborn young may also be removed from the pouch of one
female and transferred to a teat in the pouch of another female.
The clear fluid on which the newborn young is suckled is present 33-days
after estrus whether the female has mated and become pregnant or not.
Females which have never been mated will raise young transferred to their
pouches provided that the transfer takes place 33-days after oestrus.