Birth of the red kangaroo (1965)

[A kangaroo appears on screen with text: Produced by the CSIRO Film Unit and the Division of Wildlife Research Australia]

[Text changes: Birth of the Red Kangaroo]

[Image changes to show a red kangaroo with a joey poking out of her pouch]

Narrator: In one form or another the unusual way in which marsupials are born has been the subject of strange myths and legends for hundreds of years.

[Image changes to show a dated map of Australia and then the pages of a book that include a sketch of a ship as described below by narrator]

The early navigators made many observations on kangaroos and wallabies as they explored the coast of the Great South Land. Perhaps one of the earliest was the Dutch merchant François Pelsaert who ran aground on the Abrolhos Islands off the coast of Western Australia in 1628.

Despite the fact that his ship was wrecked and some of the crew had mutinied, Pelsaert was sufficiently observant to record some interesting notes on the Tammar wallabies, which live on these remote islands.

[Image changes to show a tammar wallaby]

Pelsaert: Their manner of generation is exceedingly strange and highly worth observing. Below the belly the female carries a pouch inside which are the teats and we have found that the young ones grow up in this pouch. We have seen young in the pouch which were only the size of a bean, so that it seems certain that they grow there.

[Image has changed to show a pouch being stretched open to reveal a baby wallaby]

Out of the teats from which they draw their food. The young occupy the pouch until they are grown up and able to walk and then after keep creeping in to the pouch when they are hunted.

Narrator: By suggesting that marsupial young grew from the teat, Pelsaert and others created a myth which persists to the present day.

[Image has changed back to a red kangaroo lying on the ground. Tails and a leg can be seen popping out of her pouch]

The effects of birth in kangaroos and other marsupials were not finally known until scientific studies were made of all aspects of their reproduction. Most of these investigations have been carried out with red kangaroos in captivity and this film has been complied during these observations.

[Camera pans over a semi-arid landscape and then back to the red kangaroos]

In the wild red kangaroos live and breed throughout most of inland Australia where the annual rainfall is less than 20 inches. The red kangaroo is well adapted to these semi-arid conditions and unlike most other marsupials it breeds all through the year. This seems to be a very efficient form of adaptation to the environment for if they had a regular breeding season there could be frequent failures of whole generations of young because they were born at times unfavourable for their survival.

The red kangaroo seems to avoid these catastrophes by having young enter the population at all times of the year. Those that leave the pouch at time when they can find sufficient food and water survive. Those that do not, perish.

[Image changes to show a male and female kangaroo grazing on grass. The male kangaroo has red fur, whereas the female has grey fur]

In the red kangaroo only the males, like the one in the background, have the characteristic rusty red fur.
The females, in the foreground, are usually blue grey in colour, often referred to as blue flyers or blue does. In some areas variations of colour can occur in either sex.

[Image changes to show a graph marking the female kangaroos reproductive pattern]

As in many other mammals, female red kangaroos have a cyclic reproductive pattern. The unmated female has a period of oestrus or sexual receptivity every 35-days.

[Image changes to show a graph marking the male kangaroo’s reproductive pattern]

The male is continuously fertile and will mate with a female whenever she is in oestrus.

[Image has changed back to the male and female red kangaroo involved in the mating process as narrator describes below]

The male becomes aware of the approaching sexual receptivity and begins to follow the female. Such behaviour may start two or more days before mating and at times the chase may be energetic. He smells the pouch and the external genital opening and quite often grasps the tail of the female.

Once full sexual receptivity is obtained the female stands for the male and copulation occurs.

[Image changes to show the male and female kangaroo copulating]

This may last for up to 20-minutes. If mating is not observed it may be diagnosed from the vaginal smear. A collection of cells from the vaginal tract of the female.

[Image changes to show a sample being taken from the kangaroo’s vagina]

The sample is then placed on a slide and under the microscope sperms can be seen in the vaginal smears of kangaroos which have recently mated.

[Camera zooms in on the image of sperm produced by the microscope]

[Image has changed to show an animation of the female red kangaroo’s reproductive organs and the parts that make it up are described by the narrator]

The reproductive organs of the female red kangaroo lie in the body cavity just behind the pouch and consist of two ovaries, two fallopian tubes and two uteri. The two uteri open separately into the anterior vaginal sinus. The walls of this canal are thin and capable of great extension after mating as they become filled with seminal fluid. The two lateral vaginae are much narrower canals with a thick muscular wall. The median vagina forms a direct connection between the interior vaginal sinus and the urogenital sinus; it is down this median vagina that the young kangaroo passes at birth.

If we section this drawing we will be able to follow more easily the various stages of fertilisation and pregnancy.

[Image changes to an animation of the sperm moving along the reproductive organ]

After mating the sperms passes up the two lateral vaginae filling out the anterior vaginal sinus and moving up into the two uteri. The mature follicle which has developed in one ovary bursts just after oestrus and a single egg is shed.

[Image changes to an animation of the egg moving down the tube into the uterus]

This egg is fertilised in the fallopian tube and moves down into the uterus. The follicle collapses and is replaced by a corpus luteum an endocrine organ which produces the hormone of pregnancy, progesterone.

Now, the embryo starts the development which will last for about 33-days.

[Image changes to an animation of the embryo beginning to grow; it is represented by a white dot that is getting larger and larger]

The embryo is surrounded by the yolk sack and a number of membranes. Throughout this period there is no way of telling whether a female kangaroo is pregnant or not, this can only be diagnosed by opening up the animal and finding a developing embryo in one of the two uteri. However, the pregnant female is immediately distinguished from the non-pregnant one during the several hours just before birth.

[Image has changed back to the female red kangaroo cleaning her pouch]

At this time she begins an intensive period of pouch cleaning, putting her muzzle right into the pouch, licking the lining. She also licks around the opening of the pouch, but rarely the fur between the pouch and the urogenital opening.

The female red kangaroo about to give birth takes up a normal grooming position.

[Image changes to show the female red kangaroo arranging herself into the grooming position as described below by the narrator]

The back is usually supported and the tail passed forwards between the hind legs. Now the young has completed development and starts to leave the uterus.

[Image has changed back to the animation of the reproductive tube and shows the developed embryo moving down the tube to be delivered]

It goes down the median vagina, a short cut between the uterus and the urogenital sinus. 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 sack 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.

[The newborn can be seen crawling up the females belly to her pouch]

During the early part of its climb to the pouch the young is attached by the 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 anesthetise a female with Nembutal a few minutes before the young is born.

[Camera zooms in on the urogenital opening as the ruptured yolk sack fluid leaks out of the hole]

This female is anesthetised, again, a few millilitres of fluid from the ruptured yolk sack appear just before birth.

[Camera remains zoomed in on the opening and the kangaroo can be seen coming through the hole]

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.

[Camera remains zoomed in as the newborn crawls up the belly of the kangaroo]

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 anesthetised 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.

[Camera zooms in on the newborn entering the pouch]

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.

[Image changes to show the newborn latch on to a teat]

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.

[Image changes to show the newborn being removed from the teat it is on and being placed onto another teat inside the pouch]

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.

[Image changes to show the newborn being placed inside of another pouch]

The clear fluid on which the newborn young is suckled is present 33-days after oestrus 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.

[Image has changed back to show the graph marking the female kangaroos reproductive pattern]

In most marsupials the oestrus cycle is longer than the gestation period. In the red kangaroo the oestrus cycle lasts for an average of 35-days while the gestation period is 33-days.

Pregnancy does not prevent a return to oestrus just after the young is born, however, the sucking stimulus of the new born young terminates further uterus cycling for as long as the young is suckled in the pouch. Because a female kangaroo returns to oestrus a few days after giving birth mating and fertilisation can again take place.

[Image changes to show the same animation of the female kangaroos reproductive organs]

This postpartum mating is similar in many respects to the mating earlier in the film, this time however, the developing follicle is in the left hand ovary. The recently vacated and partly collapsed uterus is in on the right.
Again, sperms enter the uterus.

[Image changes to show an animation of the sperm moving through the reproductive organs]

The follicle bursts shedding a single egg which is fertilised in the fallopian tube. The fertilised egg descends into the uterus but only develops to a blastocyst stage with little or no change in actual size. This is because the sucking stimulus of the young already in the pouch prevents the complete development of the embryo.

[Camera zooms in on dormant blastocyst]

This dormant blastocyst now remains in a partly developed state while the first young grows up in the pouch, usually about 200-days.

[Image changes to show the pouch being peeled back to reveal a suckling joey]

As this first young grows the composition of the milk gradually changes to become thick and white, quite different from the clear fluid on which the newborn young was fed. It is a remarkable feature of kangaroo reproduction, but when two young of different ages are being fed at the same time the mother is producing milk of two different compositions.

In this pouch the four month old young is feeding from a teat which has become greatly elongated. On the right is a second elongated teat on which the previous young, now out of the pouch, is feeding.

[Camera zooms in on the teats inside the pouch]

Not until it is about 150-days old does the young first put its head out of the pouch.

[Image changes to show a kangaroo laying down and a joey can been seen poking its head out of the pouch]

Soon afterwards it begins to eat grass from a position in the pouch. By the time it’s about 200-hundred days old it makes the first short journey from its mother.

When the 200-day old young starts to leave the pouch the sucking stimulus is lessened and the blastocyst resumes development.

[Image has changed back to the animation of the kangaroos reproductive system and zooms in on the growing embryo]

This also happens if the young is lost prematurely. After about 31-days the new embryo is ready to be born. The young out of the pouch stills feeds from the elongated teat which it occupied throughout pouch life and which it now grasps from the outside. Under ideal circumstances adult female red kangaroos produce one young every eight months. Since each young is dependent on its mother until it’s about 12-months old, females are frequently accompanied by a juvenile while suckling a young in the pouch.

Although François Pelsaert’s observations in 1628 were inaccurate his interest in the details of marsupial reproduction is a tribute to his enquiring spirit.

Pelsaert: Their manner of generation is exceedingly strange and highly worth observing. Below the belly the female carries a pouch inside which are the teats.

Narrator:The facts of marsupial birth have been more accurately observed in recent years and are still highly worth observing.

[Image has changed back to show the newborn climbing up its mother to found her pouch]

The production of a very small young which climbs virtually unaided into the pouch and develops as an externalised foetus is common to all marsupials. In red kangaroos the off spring rarely fails to find the teat and fertilisation immediately after birth ensures that the female has a reserve embryo should the first fail to complete pouch development. Although this mechanism is remarkably different from that in other mammals it is highly efficient and seems well adapted to the environment in which these marsupials live.

[Image has changed back to show a red kangaroo in its natural environment]

[Credits roll: Scientific direction, G. B. Sharman. Assisted by Meredith J. Clark, J.H. Calaby, J.C. Merchant. Camera Ederic Slater, David Corke. Editing David Corke. Animation Perce Watson. Production Stan Evans]

[Text appears: The End]