Location & Habitat

The platypus can be found along the eastern coast of Australia, in its rivers, streams and lakes. They can be found as far north as the Annan river in northern Queensland, and as far south as Tasmania. The orange area in the diagram below shows the location of the platypus throughout Australia.

The platypus is much more common in the Southern parts of Australia than it is in the Northern parts. This could be due to two factors, these being the presence of crocodiles and a greater threat from flooding. Since the female platypus does not begin to breed until she is two years old and even then she may not breed on an annual basis could mean that the platypus has difficulty in maintaining a population in the presence of crocodile predation and flooding.

In the areas that the platypus has maintained a population, it is clear though that this is a population of individuals rather than of families. The platypus is predominantly a loner, who has its own specific home range, in which it lives and feeds. One platypus's home range may overlap with that of another (Serena, 1994). But it is unknown as to how territorial the platypus is and whether there are confrontations to see who controls a specific area. But when there is overcrowding area, it is usually the responsibility of the juvenile platypus to leave the area and find a home range of its own.

Within these home ranges there are several burrows located along the river bank that the platypus may use. There appear to be two types of burrow; dwelling burrows and nesting burrows. The more complex ones are used for rearing young, whereas the other, more simple, ones are used by both sexes on a day-to-day basis for resting, sleeping and eating. However, it has been suggested (Grant, 1989) that the more complex nesting burrows are a result of digging over a period of time, which have developed the simple tunnel of the dwelling burrows into a more complex 'warren-like' series of tunnels, rather than have been specifically dug for the purpose of nesting. It has often been thought that the entrance to both these types of burrows were predominantly above the water level. But research has shown that the entrances to the dwelling burrows are often underwater (Serena, 1994).

These burrows, as with many other types of tunnels, often have a problem with maintaining a flow of air through them. So if a platypus stays in a burrow, for a certain period of time, it will begin to use up the available oxygen. During the breeding season this lack of oxygen would appear to have greater significance for two reasons. The first is that, during breeding, the female will plug the burrow's entrances every time she leaves or returns to it, and the second is that the young platypus usually remain in the nesting burrow for about 3 months with a slowly diminishing amount of oxygen. It is possible that the platypus has adapted the chemistry of its blood so that it can make the best use of the limited oxygen supply, but further research is required. It has been suggested by Serena (1994) that the nesting burrows deliberately have their entrances above water in order to increase air flow, whereas it is not so important for the camping burrows. It may also be that the position of the nesting burrow entrance hole is to protect the young from the affects of flooding.   

Description & Behaviour

It was originally thought that the first platypus specimens that were sent to England, were nothing more than an elaborate hoax. This was a fairly logical reaction to an animal that would seem impossible because it had a muzzle like a duck's bill, a tail like a beaver and which laid eggs but suckled its young. All of these attributes seemed contradictory to the knowledge scientists had in those days. But since then a lot of investigation has been done in order to find out more about this 'hoax' of a creature.

The platypus is roughly half the size of a household cat. The adult male's average length is about 50cm and its weight is approximately 1.7kg. The female, however, is smaller and will reach an average length of 44cm and weigh about 0.9kg. This difference in size and weight between the males and the females is called sexual dimorphism. See the table below for more information about the size of platypuses.

(Table adapted from Grant, 1989)

The platypus has a thick covering of waterproof hair over all of its body, apart from on its feet and its bill. The outer hair is dark brown on its back and yellowish on its underside. Under this outer hair, which is long and coarse, there is a fine, dense under-fur which has a similar feel to wool and ranges in colour from grey to dark brown.

The tail of the platypus is mainly made up of a fatty tissue that is used to store energy supplies, which the animal can use when there is a shortage of food, such as in the winter months. The top is covered by coarse hairs, whereas underneath there is only a sparse growth of hair. The platypus's tail differs from that of a beaver's both in it's shape and the purpose it is used for. The beaver's tail is flatter, broader and covered in special scales, and it is used to help the animal propel itself through the water. The platypus, on the other hand, uses its tail only for steering while swimming.

The platypus's body is flat, streamlined, and has short legs. The front feet are webbed, which make the platypus ideally suited for swimming. This it does by alternatively kicking its front legs in order to propel it through the water, and the hind legs, which are only partially webbed, acting as steering rudders. These webbed feet could be the reason why the platypus is called a platypus. This is because the webbed feet may give the impression that the platypus is flat-footed, which is what platypus means.

When out of the water and moving around the webbing is folded under the animal's feet, in order to prevent damage occurring and to uncover broad nails, which are ideally suited for digging. On each of the hind legs of the male there is a 1.5cm long horny spur on the ankle. The spur is hollow and is linked to a poison gland in the thigh by a duct. Juvenile females also have a rudimentary version of this spur, which is lost within their first year.

The platypus has a flexible, duck-like bill, which is soft, flat and rubbery, and is very sensitive to touch. This is due to its large supply of nerves. The platypus uses its bill in order to search for food and to find its way around when it is submerged. The top of the bill is a blue-grey colour and slightly back its tip are two nostril holes. The positioning of these allow it to breathe while the rest of its body is submerged. The lower bill, which is a pale pink or mottled colour on its underside, is smaller than the upper bill. At the back of the bill is the frontal shield that stretches slightly up and over the forehead. It is unknown as to what its purpose its.

Since the platypus does not have any teeth it has to grind its food using grinding pads that can be found on the upper and lower surfaces inside its mouth. The lower bill is held in place by two elongated dentary bones. This structure can be found in all mammals, whereas other vertebrates, e.g. reptiles, have a lower jaw which is made up of several pairs of bones.

There are two grooves situated on either side of the platypus's head, just behind the bill. These contain the eyes and the ear openings. The platypus has no external ear lobes. When diving, the platypus closes both its ears and eyes. This means it has to rely on other organs for finding its way about underwater, hence the sensitivity of its bill. However, when on land it has the use of its eyes which are very acute over long distances. But because of their location it is unable to see what is literally 'under its nose'.

It has been reported that the platypus is capable of making noises. These include a growl that is similar to the one a puppy would make and a noise that is comparable with that of a brooding hen. They are believed to be used when the animal is in danger. An example of this noise can be heard at this site.   

Throughout the year the platypus is faced with changes in temperature, both on the land and in the water. Since it is a mammal, and therefore warm blooded, it needs to have developed ways in which it can adapt to these conditions in order to continue to live. The table below shows the sort of changes in temperature that a platypus may live through in a year.

(Table adapted from Grant, 1989)

Even during the winter when it is considerably cold, the platypus still goes swimming in search of food. The fact that it can remain active within such a cold environment casts doubt on the idea that it might be a reptile, since it is well known that when it is cold, reptiles have a reduced metabolic rate causing them to become cold and lethargic. If the same reduction in metabolic rate was to happen to a platypus, then it would be unable to go looking for food on the river bed. The result of this would be that it would greatly reduce its chances of survival during the cold winter period. So it has learned to adapt to this cold environment in a variety of different ways.

The colder the external environment the greater the heat the platypus needs to generate in order to maintain a balance between its normal body temperature (approximately 32°C) and that of its surroundings, which is called the thermal gradient. It does this both internally and externally. By increasing its metabolism, heat is produced. But this metabolism requires energy in order to generate the heat. The more heat that is required the greater the increase in metabolism is needed, and thus the greater the amount of energy that is required. This presents a potential problem in winter because it is harder to obtain the necessary food, i.e. energy, due to its scarcity.

The platypus also uses its blood circulation to carry the heat, that its metabolism has generated, to the parts of the body that require it, and reduce the circulation to the areas that do not, such as the hind legs, tail and bill. Body heat is also maintained by its waterproof fur. This traps a layer of air, which provides good insulation against the cold.   

Diet & Feeding

The platypus eats a variety of food, including invertebrates, small fish, fish eggs, frogs, and tadpoles. The time of year will dictate which food the platypus can eat. The table below gives an outline of the sort of food a platypus may eat at different times of the year.

(Table adapted from Grant, 1989)

Normally the platypus will spend about half the day eating. According to metabolic studies, the platypus eats about 25% of its body weight per day. Whereas studies of captive animals feeding seem to show that they eat about half their body weight in food. During the summer, the platypus is likely to eat more than in the winter, and then stores this excess as fat in its tail. This food supply is then used to help sustain it through the leaner winter months and to assist it in the spring when a lot of its time is taken up with mating and breeding.

The platypus searches for its food by diving to the bottom of streams and rocking its head from side-to-side through the mud. These dives can last for about 40 seconds (Kruuk, 1993) and during this time the platypus searches for food using two different types of sensory organs located on the bill. One of these is affected by touch, whereas the other one is triggered by electrical stimulation. It is believed that this second method is only used by the platypus and a few fish (Anderson, 1988). It has also been suggested that the platypus uses the electrical fields created by the movement of streams to locate its position near the bottom (Anderson, 1988).

The platypus has developed its own method of eating its food, since it has no teeth. Once it has captured some food in its bill, it then transfers it to the cheek pouches located behind the bill. The platypus then returns to the surface and the pouch contents are then moved to the mouth area of the bill. Here the food is ground between two grinding pads located on the upper and lower jaw. On the sides of the lower jaw there are horny serrations which are used to expel the unwanted parts of the food, e.g. shells, mud, etc..   

Reproduction

Breeding does not occur until the platypus is at least two years old. This is partly due to the fact that the male is unable to produce sperm until he is in his second year and that the female does not always breed each season. In order for mating to occur the female's reproductive organs and the male's testes increase in size. They reach their maximum size between July and August, which is when mating occurs.

During this time the female's body also adapts so that she can produce milk for her young from two nipple-like structures on her abdomen which are surrounded by hair. It is believed that the young obtain this milk by prodding these two areas which cause the milk to be discharged on to the hairs, which they then drink.

Little is known about the mating/courtship behaviour of the platypus, but observations of captive animals has provided some evidence with regards to this process. It starts with the male and female swimming, close enough to each other so that they can make contact. This sort of behaviour is largely initiated by the female. From this demonstration of her interest in copulation, the male will then grab her tail in his bill. From this position he climbs partially onto her back in order to obtain a suitable position for copulation. He then curls his tail round under her abdomen, so that the penis in his cloaca (single 'hole' for urination, defecation and fertilisation) can be inserted in to the female's cloaca, which is where her reproductive area is. If successful, fertilisation will occur.

It is not known how long the gestation period lasts. But the echidna lays a similar sized egg and it's gestation period is about one month, so it is possible that there could be some similarity in gestation time. The female can produce between one and three eggs, though the usual number is about two. These eggs are about 16 to 18mm long and 14 to 15mm wide. They are reptilian-like in that they are sticky and have a soft skin. Once the eggs are laid, the mother starts to incubate them in the nesting chamber of the burrow, which is about 30cm square and is lined with a mixture of dead and green vegetation.

But, unlike the echidna, the female platypus does not have a pouch, so she curls her body around the eggs in order to incubate them. This lasts about 10 to 12 days, resulting in the hatching of a young platypus about 18mm long. The young then remain in the burrow, suckling on their mother's milk, for about 3 or 4 months.

While they remain in the nesting burrow they will grow to approximately 80% of their adult size, yet their weight will only increase to about 60% of that of an adult. After leaving the burrow they will remain suckling from their mother until they are able to provide food for themselves.   

Protection

The platypus is a shy creature that will attempt to swim away and avoid aggressive situations. This may involve spending longer underwater, possibly up to 10 minutes, and at the same time not giving off any tell-tale bubbles that would indicate its position. However, during the breeding season the male platypus is likely to become aggressive towards potential competition. This aggression is predominantly demonstrated with the use of the poisonous spur located on his hind legs. These spurs are hollow and are connected to a sac of poison, which is pumped through the spur and into the object that it has pierced. It has been known that this venom can kill dogs and other platypuses/platypi, but wild platypuses/platypi have been found with injuries sustained by spurs, yet they have survived.

It is unknown as to the extent to which other animals prey on the platypus. Foxes and birds of prey are believed to be two types of animals that use them as a food supply, especially the young platypuses. In the north crocodiles may also present a potential danger to their survival in such areas. In the past, the platypus used to be hunted for its pelt but they are now protected by laws, including the National Parks and Wildlife Act, 1974.   

Social Aspects

The platypus is primarily nocturnal in its behaviour, though it can often be seen at dusk and dawn. Male and female platypuses tend not to come into contact with each other, except during the mating season.   

Environmental Influences

During the spring, flooding may occur in the southern areas of Australia, whereas they are more likely to occur during the summer in the northern areas. These floods may affect the platypus because some of their burrows may become flooded.. It is unlikely that these floods cause fatalities in adult platypuses, but there may be fatalities amongst young platypuses. It is unknown how the platypus endures these floods until they have subsided. It has been suggested that they may inhabit rabbit burrows or hollow logs and feed from nearby backwaters, only returning to the flooded areas after they had subsided. Whatever method they use during these raised water levels, they are obviously successful otherwise it would not have survived for so many millions of years.   

History

Outside of Australia and New Guinea, there are no living relatives of the monotremes. On the whole, little is known about the ancestry of the platypus. But a variety of different fossils have been found that seem to show that the platypus had ancestors that were quite similar to itself. One of these is Obduron insignis, which is thought to have lived about 15 million years ago. It is different to the platypus in that it is believed that it retained its teeth into adulthood and thus did not use grinding pads for chewing its food, which the platypus does. A possible fossil of this animal has been found in Patagonia (South America), that is believed to be about 62 million years old (Thwaites, 1991). Evidence from a bone analysed by Meng & Wyss (1995) seems to suggest that the monotremes are related to the long extinct multituberculates.

The platypus has been called a variety of different names. Originally it was called duckbill, watermole, duckmole and platypus by the Europeans who first came into contact with it. Then in 1799 (Grant, 1989) it was given the name of Platypus anatinus, which simply means a flat-footed, ducklike animal. But the Platypus part of this name was changed to Ornithorhynchus which means birdlike snout. The Aborigines also gave the platypus a variety of names, which included mallangong, boondaburra and tambreet.   

References

Anderson, I., 1988. 6th Sense is the Platypus secret. New Scientist. 118(1612), p.39.

Encyclopaedia Britannica. 1995

Grant, T., 1989. The Platypus. A Unique Mammal. New South Wales: New South Wales University Press.

Kruuk, H., 1993. The diving behavior of the Platypus (Ornithorhynchus anatinus) in waters with different trophic status. Journal of Applied Ecology, 30(4), pp.592-598.

Meng, J., & Wyss, A.R., 1995. Monotreme affinities and low-frequency hearing suggested by multituberculate ear. Nature. 377, pp.141-144.

New Scientist. 1986. The battery-operated Duck-Billed Platypus. New Scientist. 109(1495), p.25.

Serena, M. 1994. Use of time and space by Platypus (Ornithorhynchus anatinus, Monotremata) along a Victorian stream. Journal of Zoology. 232(1), pp.117-131.

Thwaites, T., 1991. Duck-billed Platypus had a South-American cousin. New Scientist. 131(1783), p.13.

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