Distribution and Status
The platypus now only occurs in Australia.
However, from fossils discovered in Argentina, we know that the ancestors of platypus were found in South America as well as Australia until at least 60 million years ago - when the two land masses were still joined together as part of the southern supercontinent Gondwana.
The platypus lives only in Australia. Populations occur in Tasmania, Victoria, New South Wales and Queensland to about as far north as Cooktown. In South Australia, apart from an introduced population surviving on Kangaroo Island, the species is considered rare and possibly extinct in the wild.
(Distribution of platypus (shaded area) in Australia)
Platypus occupy a wide variety of permanent streams, rivers and lakes and may also use temporary or manmade water bodies, particularly when these are linked directly to streams or rivers.
Although the fossil record shows the occurrence of several different platypus-like species, today Ornithorhynchus anatinus is the only known platypus.
Platypus do vary somewhat from place to place - for example, animals from Tasmania are somewhat bigger on average than their counterparts from Queensland. However, no sub-species or distinctive local races are currently recognised by scientists.
The platypus is officially classified as "Common but Vulnerable" in Australia. As a species, it is not currently considered to be endangered.
However, platypus populations are believed to have declined or disappeared in many catchments, particulary in urban and agricultural landscapes. In most cases, the specific underlying reasons for the reduction in numbers remain unknown.
Number of platypus
Platypus surveys have only been carried out in a few catchments in eastern Australia. It is therefore impossible to provide an accurate estimate of the total number of platypus remaining in the wild.
Based on recent studies, the average platypus population density along relatively good quality streams in the foothills of Victoria's Great Dividing Range is only around one to two animals per kilometre of channel. Because platypus are predators near the top of the food chain and require large amounts of food to survive (up to about 30% of a given animal's body weight each day), it is believed that their numbers are most often limited by the availability of food, mainly in the form of bottom-dwelling aquatic invertebrates.
Until the early twentieth century, platypus were widely killed for their fur. The species is now protected by law throughout Australia.
The Search for Food
A platypus must eat relatively large quantities of food to survive - equivalent to about 15-30% of a given animal's body weight each day. Because platypus usually defecate in the water, their droppings are only rarely encountered. However, after analysing bits of food remaining in the animals' cheek pouches, scientists have concluded that the platypus diet mainly consists of freshwater invertebrates such as shrimps, worms, yabbies, pea-shell mussels, and immature and adult aquatic insects (including mayflies, dragonflies, caddisflies, stoneflies, aquatic beetles, and water bugs). Small frogs and fish eggs are also eaten occasionally, along with some terrestrial insects that fall into the water from overhanging vegetation.
A small amount of aquatic vegetation may possibly be ingested by platypus when feeding. However, it is unlikely that this constitutes a significant part of their diet, particularly as vegetable matter would not provide sufficient energy to fuel the active life-style of the platypus.
The platypus hunts in the water, mostly at night. Hearing and vision are therefore of little use in detecting the small aquatic invertebrates on which the animals primarily feed. Reflecting this fact, a platypus protects its eyes and ears by automatically closing them underwater and instead relies on its bill to locate prey. The upper and lower bill surfaces are packed with hundreds of receptors which respond to touch and the tiny electric currents produced when invertebrates move in the water. These receptors are also believed to be vital to the platypus's ability to navigate successfully among rocks and other obstacles when submerged.
Platypus are specifically adapted to forage in the water and there are no reliable records of the animals feeding on dry land, although they sometimes search for prey at the water's edge by digging under rocks or among the roots of streamside plants.
While diving, the platypus temporarily stores small food items in special cheek pouches. When the animal returns to the surface to breathe, the food is ground up very finely between rough pads located inside the bill. While juvenile platypus have proper teeth, these fall out soon after the young first enter the water.
Platypus are active mainly at night. However, they can sometimes be seen feeding during daylight hours, especially in areas where the animals are very numerous or when the sky is overcast.
Platypus do not appear to hibernate, but observations in both captivity and the wild suggest that some individuals may periodically enter a state of torpor in which the animals allow their body temperature to drop, remaining inactive for up to about six days. Almost nothing is known of the conditions which trigger this behaviour, apart from the fact that it has only been recorded in the colder months of the year (late May to early September).
Platypus in captivity
Platypus are wild animals with specialised living requirements. It is illegal for members of the public to keep them in captivity. A platypus which has been accidently captured along a stream or found wandering in an unusual place should never be taken home and treated as a pet, even for a brief time. The animal will not survive the experience.
Only a small number of Australian zoos and universities hold permits to maintain platypus in captivity for legitimate display or research purposes. Current Australian government policy does not allow this species to be taken overseas for any reason.
Out of the water
Platypus are air-breathing mammals, and by choice spend up to 17 hours a day resting out of the water in an underground burrow. However, they feed only in the water and are rarely observed on land for more than a few minutes at a time. Many of the platypus found in unusual locations, such as suburban gardens, appear to be young animals that are orphaned or have dispersed from their mother's home range in order to claim their own territory.
What do platypus burrows look like?
Platypus use two types of burrows: "nesting burrows" (which provide shelter for a mother and up to three offspring) and "camping burrows" (all other burrows). In both cases, the burrow chambers are just big enough to accommodate their occupants - for example, a nesting chamber containing two young platypus (estimated to be a month old) along Lockyer Creek in Queensland was 25 centimetres wide x 46 cm long x 20 cm high, while a camping chamber known to be used by a subadult male along Badger Creek in Victoria was 20 cm wide x 30 cm long x 14 cm high.
The tunnel leading to a camping burrow chamber is usually quite short (1-4 metres long). Camping burrow entrances are usually difficult to spot, being located underwater or just at the water's surface and often hidden by overhanging vegetation or an undercut bank.
Where are platypus burrows found?
Platypus select burrow sites partly on the basis of bank height, with nearly all burrows found in banks rising one metre or more above the water.
As well, platypus prefer to place their burrows along moderately undercut banks where substantial vegetation overhangs the water. Such banks are normally well consolidated by plant roots, so that undercutting is confined to the part of the bank extending just above (as well as below) the water surface. The amount of cover provided along the bank top by shrubs and low-growing plants has also been found to be significantly greater than expected at platypus burrows located along the Yarra River near Melbourne. Besides helping to protect platypus burrow entrances from predators, this combination of habitat characteristics reduces the likelihood that burrows are damaged by erosion.
How many burrows does a platypus use?
An adult platypus will normally occupy several different camping burrows (up to about a dozen) within a period of a few weeks. By having numerous burrows scattered across the entire length of its home range, a platypus is always reasonably close to a safe refuge. As well, using different burrows on different days may reduce the proliferation of parasites (such as the platypus tick, Ixodes ornithorhynchi) at any one location. Two grown platypus will sometimes share a burrow at the same time, though males and females both tend to be solitary in their habits.
Do platypus ever spend the day resting in places other than burrows?
Radio-tagged platypus have occasionally been found sleeping inside a hollow log at the edge of the water or within a pile of woody branches accumulated in the stream channel.
Matters of Life and Death
The platypus is a warm-blooded mammal which lays and hatches eggs. A female platypus produces a clutch of one to three eggs in late winter or spring. The eggs are 15-18 millimetres long and have a thin, leathery shell, like those of snakes and lizards. The mother is believed to incubate them between her lower belly and curled-up tail for a period of about 10 or 11 days as she rests in an underground nest made of leaves or other vegetation collected from the water.
A female platypus does not have nipples. Instead, a rich milk is secreted from two round patches of skin midway along the mother's belly. It is believed that a baby platypus feeds by slurping up milk with rhythmic sweeps of its stubby bill. When the juveniles first enter the water at the age of about four months, they are nearly (80-90%) as long as an adult.
Male platypus do not help to raise the young.
Platypus eggs have been recorded in nests from August to October, with some evidence that the animals breed a few weeks earlier in Queensland as compared to Victoria and Tasmania. As platypus eggs are believed to develop for about a month inside the mother after being fertilised, platypus presumably breed as early as July in the warmer parts of their range.
Male and female platypus are both believed to be capable of first reproducing at the age of two years. At maturity, male platypus measure on average 50 centimetres in total body length (bill tip to tail tip). They typically weigh 1.2-2.6 kilograms, although the heaviest platypus yet recorded (captured in Tasmania) tipped the scales at 3 kilograms. Adult females are smaller, measuring an average 43 centimetres in total body length and weighing 0.7-1.6 kilograms.
Platypus have been recorded to live to at least 16 years in the wild, though most individuals die at a much younger age. The longest reliable age record for a platypus in captivity is 17 years. More research is required to establish the animals' typical life span in the wild, although estimates of about 4-5 years for males and 6-8 years for females are not unreasonable.
Determining the exact age of a wild adult platypus is very difficult. In the case of younger animals, some information can be gained by examining the inner hind ankle. From the time they first leave the nesting burrow, juvenile males are equipped with a conspicuous cone-shaped spur (initially about 1 centimetre long) on each hind leg. At first the spurs are protected by a white chalky layer, which gradually chips away to reveal the slightly curved true spur by the age of about one year. Juvenile females have tiny spurs, 1-2 millimetres long, which are shed by the age of about 10 months, leaving only a small pit to mark the spot.
Platypus do not seem to make any calls or loud vocalisations. Occasionally, when disturbed or threatened, a platypus may make a soft growling noise. However, this is so quiet that it can only be heard at very close distances.
Platypus can also occasionally be heard sneezing but again, only at very close quarters. Such sneezing is probably an automatic reflex to clear residual water from their nostrils, which are located on the upper side of the bill.
Reports by naturalists indicate that very large Murray cod and birds of prey (hawks, eagles and owls) occasionally capture platypus in the water, while carpet pythons and goannas may attack young platypus in the burrow. It has also been suggested that predation by crocodiles may contribute to the lack of platypus on Cape York Peninsula in far north Queensland. Since European settlement, introduced species such as foxes, dogs and cats have probably become the major predators on platypus.
Effect of floods
Anecdotal evidence suggests that some platypus may die in severe floods. However, flooding may also benefit platypus populations by temporarily expanding the size of the area available for foraging.
Few life-threatening illnesses have been reported in wild platypus, other than cases of bacterial pneumonia which probably developed after water was aspirated into an animal's lungs.
Platypus living in some parts of Tasmania are also known to suffer from a fungal disease, Mucor amphibiorum, which can cause serious skin abscesses and ulcers. Fortunately, no cases of this disease have yet been found on the Australian mainland.
Life in the Water
Platypus diving ability
In captivity, a platypus has been observed to remain underwater for up to 14 minutes while resting quietly under a log. When searching actively for food, a platypus will usually remain submerged for less than a minute before returning to the surface to breathe.
Like most diving mammals, the platypus has blood that is very rich in oxygen-carrying haemoglobin and red cells. The platypus can also reduce its need for oxygen when diving by lowering its heart rate dramatically, from more than two hundred beats per minute to less than ten beats per minute.
Platypus fur is extremely fine and even denser than that of polar bears and river otters, with 600-900 hairs covering each square millimetre of skin! Platypus fur also has two layers - a woolly undercoat and longer, shiny guard hairs - which work together to trap a layer of air next to the skin, keeping most of the animal's body dry even when diving.
For the platypus to stay warm while in the water, its fur must remain completely clean and waterproof, and not be fouled by oil or other pollutants.
A healthy platypus normally maintains its body temperature at close to 32 oC, about 5 oC less than that of humans. This reduces the rate at which a platypus loses heat to the water, helping to ensure that the animals don't become chilled even when swimming all night in near-freezing conditions.
The combination of a naturally low body temperature and thick fur coat also means that the platypus overheats rapidly if exposed to warm conditions on land.
The platypus hunts underwater and, predominantly, at night. In such conditions, hearing and eye-sight are of little use in detecting prey. Accordingly, the platypus closes both its eyes and ears (which are located in a groove behind the eyes) and relies on its "sixth sense" - an electro-receptor system, located in the bill which helps it detect the small flickers of electricity produced by the aquatic creatures that it feeds on. The bill also contains various pressure sensors which, together with the electro-receptors, probably assist navigation while submerged.
The platypus was once commonly known as a "duckbill". In fact, its bill is rubbery and flexible, not hard like that of a duck. Although the bill is quite tough, to enable the platypus to search for food amongst rocks and gravel, it is covered with skin. Sometimes platypus are found with scars on their bill, suggesting that they have cut themselves on sharp objects in the water, such as broken glass and wire, or have been snagged on fishing hooks.
The platypus swims using only its front limbs for propulsion. The front feet are equipped with large webs of skin that serve as highly effective paddles. The webs are folded under the foot when the platypus is out of the water, making it easier for the animal to walk and use its strong claws for digging burrows. Unfortunately, these highly specialised front feet are not adept at removing objects that become caught around the head or body. As a result, platypus can die after becoming ensnared in litter such as loops of nylon fishing line or plastic six-pack holders.
The hind legs of the platypus help to steer and stabilise the animal when it is swimming. The back feet end in a series of sharp, curved claws that are used like a comb to keep the animal's fur tidy and waterproof.
Both the front and back legs extend out horizontally from the body, providing a powerful swimming and digging action. However, it also forces the platypus to shuffle like a lizard when walking on land or crossing shallow areas of water, making them vulnerable to predators such as foxes and dogs.
Some early reports suggested that the platypus slapped the water with its tail to make warning sounds, similar in behaviour to beavers. In fact, there is no evidence for this, although when startled platypus will sometimes make a "splash-dive" - a rapid dive in which they seem to use the tail to thrust themselves downwards quickly. This can produce quite a loud noise, and perhaps this was the origin of the tail-slapping myth.
The main function of the tail is to store up to 50% of the animal's body fat, providing an energy reserve if food is scarce. Researchers rate the general physical condition of a platypus on a five-point scale by applying a "squeeze test" to the tail in order to assess the amount of fat stored there.
A female platypus can also use her tail to collect leaves to make a nest in the breeding chamber. She then uses her curled up tail to hold eggs against her stomach during incubation.
The platypus tail is broad and paddle-like, quite unlike the tail of the Australian water-rat (the animal most likely to be confused with a platypus by observers) which is thin and also has a distinctive white tip.
Unlike the soft fur on the body of a platypus, the hair on the upper side of the tail is quite hard and bristle-like, reflecting the fact that the tail is used to push loose earth out of the way when a platypus is digging a burrow.
Earning their spurs
The platypus is the only Australian mammal known to be venomous. Adult males have a pointed spur (about 15 millimetres long) located just above the heel of each hind leg, which can be used to inject poison produced by a gland in the thigh (the crural gland).
Venom is only secreted by mature males, with production peaking during the platypus breeding season in late winter and spring. It is therefore presumed that males mainly use their spurs when competing for mates or breeding territories.
If provoked, a male platypus can use his spurs as a defensive weapon. In the days when platypus were shot for their fur, dogs were sometimes killed after being sent to retrieve a wounded male from the water. These days, people mainly get spurred when they handle a platypus which has become hooked inadvertently on a fishing line.
Platypus venom is not considered to be life-threatening to a healthy human. However, spurring is painful - in part, because platypus spurs are sharp and can be driven in with great force. As well, platypus poison triggers severe pain in the affected limb and can result in quite spectacular localised swelling.
No one actually knows how dangerous platypus venom is to other platypus. In captivity, a 15-year-old male died some days after being spurred by a younger adult in December (after the breeding season). However, it remained unclear whether the resulting tissue damage was due to the effects of poison or simply physical trauma and possible infection.
Platypus should never be handled, except in an emergency - for example, to extract a fishing hook that has become embedded in a platypus's bill. In such a situation, the platypus can be restrained by holding its body flat against the ground while the hook is carefully removed - ideally by a second person. Special care should be taken to avoid holding or supporting males (or animals of undetermined sex) from below. If it is necessary to pick up a sick or injured animal (for example, to place it in a secure bag or box before taking it to a veterinarian) the safest technique is to grip the platypus by the middle or end of its tail (but not the tail base, which an animal can reach with its spurs). To reduce struggling, cover the animal's eyes with a folded towel or item of soft clothing while it is being handled.
WHAT SHOULD I DO IF SPURRED?
If spurred, take first-aid action as for snake-bite - i.e.
immobilise the injured limb with a pressure-bandage and splint;
keep calm and avoid strenuous movement;
seek medical assistance as soon as possible.
The pain appears to be controlled more effectively by local nerve-blocking agents than by morphine-related drugs. Placing ice or cold-packs on the site of the spur wound is not advisable as this may actually intensify the discomfort.
Platypus in Country Areas
Platypus live-trapping surveys are physically quite demanding and require specialised knowledge and equipment to carry out properly. In consequence, our understanding of the distribution of platypus in most country areas is very sketchy, derived mainly from anecdotal information gleaned from reports of platypus sightings.
In New South Wales, platypus are believed to survive in all of the rivers flowing east from the Great Dividing Range, and at least in the upper reaches of 13 of the state's 16 west-flowing rivers.
In Queensland, the species has recently been reported in many of the east-flowing rivers between Cooktown and the New South Wales border, and the headwaters of three of the five river systems draining into the Murray-Darling Basin. While the animals are still common in parts of the Atherton Tablelands, they do not appear to occupy any of the waterways flowing into the Gulf of Carpentaria.
Platypus are believed to be widespread in Tasmanian waterways, including some streams passing through cave systems. The animals are also found on King Island, though they appear to be absent from the islands of the Furneaux group.
In South Australia, platypus are reported only rarely from the Riverland area of the Murray River and have not been encountered in the lower reaches of the Murray since 1960. They are believed to be extinct in the Mount Lofty Ranges. A population descended from introduced animals (originating in Victoria and possibly Tasmania) survives on Kangaroo Island.
In Victoria, platypus are thought to occupy at least 26 of the state's 31 river systems. The species still seems to be common in many places, especially parts of the Goulburn and Ovens River catchments and waterways in the Otway Ranges and East Gippsland. Along the Murray River, there are few recent reports of platypus downstream of Echuca. The species may have disappeared from Tidal River on Wilson's Promontory and rivers along the Portland Coast.
Because so little is known about the status of platypus, it is impossible to say in most cases whether local populations are secure or declining. However, based on the results of the Australian Platypus Conservancy's studies along the Wimmera River, platypus are probably facing severe problems in some rural catchments.
Factors which can have a serious impact on platypus numbers include:
* Reduced or seasonally altered river and stream flows.
* Declining water quality.
* Loss of native vegetation along waterways.
* Increased erosion along banks and channels.
As well, predation by foxes and feral cats, deaths caused by illegal fishing nets and traps, and injuries due to rubbish may all hurt platypus numbers, while misuse of chemicals (such as pesticides, herbicides, surfactants and fertilizers) near waterways can disrupt the aquatic food chain, greatly reducing the platypus food supply.
Case study - Platypus in the Wimmera Catchment
In 1997, the Australian Platypus Conservancy began a major study in the upper catchment of the Wimmera River in western Victoria. The research was designed to provide baseline information to a coalition of eleven local Landcare groups, banded together under the title Project Platypus, which was working to address environmental problems, including severe erosion and increasing dryland salinity. In particular, it was considered important to determine precisely where platypus still occurred in the catchment, and what actions would contribute most effectively to improving their habitat. Given the dearth of information on the factors which primarily limit platypus populations in farming areas, it was expected that the program's outcomes would also be of value in helping to shape waterway management programs in other catchments supporting agricultural activities.
The ongoing research program includes four main elements:
* Wimmera Platypus Watch. Creating a database of local platypus sightings has been useful in helping to map the animals' distribution in the catchment. Associated publicity has also helped to improve community awareness of platypus conservation issues.
* Platypus surveys. Live-trapping surveys are providing reliable information on the status of platypus populations in different parts of the catchment, and establishing the basis for longer-term monitoring.
* Landholder interviews. Interviews with landholders on properties along the main river channel and selected tributary streams in the study area are being undertaken to help define the animals' former distribution, establish when they disappeared from specific areas, and canvass local opinion as to the factors which have been primarily responsible for the species' decline.
* Studies of platypus ecology and behaviour. By tracking the movements of radio-tagged platypus and describing their burrows and feeding sites, key habitat attributes of the channel and bank in relation to the animals are being identified across different seasons.
In the period September 1997 to November 1999 the Conservancy conducted ten major fieldwork expeditions to the Wimmera. Over 125 sites were surveyed along more than 140 kilometres of the main river channel and all its major tributaries in the upper catchment. Platypus were found to occur in moderately high numbers in the uppermost part of the catchment near the Pyrenees Range, with more than 90 individuals found near the townships of Elmhurst and Warrak. Elsewhere, very few platypus were encountered - in all, over 80% of the platypus caught were found in only 25% of the area surveyed - confirming observations by local landowners that the species had declined over much of its traditional range.
The animals generally appeared to be healthy, although a high rate of scarring was observed on the bill, head, front feet and tail, probably due to encounters with barbed wire fencing in the water. Unfortunately, very few platypus were encountered elsewhere in the catchment. These results were supported by local anecdotal accounts that platypus have declined in the region over the past two or three decades in response to accelerating land and water degradation. The results of the first phase of radio-tracking studies along the Wimmera showed that in winter the animals significantly prefer using parts of the waterway shaded by trees and having substantial amounts of woody debris (logs and branches) in the water.
Because the platypus is such a popular "flagship" for freshwater conservation, this research project continues to have an important role in motivating landowners to improve the environmental quality of their local waterways and since 1999 the Conservancy has developed an on-going survey program to monitor the core platypus population areas. Community interest in the outcome of the platypus survey program has been very keen from the outset, with many landholders joining researchers at dawn to see animals being released back to the wild. These occasions have provided an ideal forum for researchers to answer questions about platypus and also provide feedback on how best to manage riparian habitats with respect to wildlife.