platypus

When the first preserved specimen reached England in 1798, this uniquely Australian mammal was thought to be a hoax. Being warm blooded, fur bearing and having mammary glands, yet having a

reproductive system similar to that of reptiles and birds, the animal certainly confused the early taxonomists! Ornithorhynchus anatinus, along with another enigmatic species, the Echidna, were placed in the order Monotremata meaning 'one hole' because of the single opening for the digestive, excretory and reproductive systems.

Habitat and Distribution
The platypus is adapted to both tepid and icy waters and populations are found in most freshwater rivers, streams, lakes, reservoirs, dams and swamps east of the Great Dividing Range from Cooktown to Tasmania. West of the Dividing Range, platypus are found only where permanent water exists. Mainly nocturnal and crepuscular (active at dawn and dusk), platypus can occasionally be seen during daylight hours, particularly during late winter and early spring when females feed frequently to build up fat reserves in preparation for breeding and egg laying. Sensitive to sudden noise and movements, this secretive animal usually disappears at the first sight or sound of disturbance. On our excursions, we regularly have excellent views of this shy and elusive animal and have often observed interesting interactions between individuals and with other species.[Platypus Observations]

General Description
It is surprising to most people that platypus are quite small in size. The north Queensland animals are the smallest, with males measuring up to about 45 cm in length and weighing up to 1300 grams, and females about 42 cm and averaging 800 grams. Animals from southern populations are usually larger, with males up to 60 cm in length and weighing up to 2,500 grams. Research has shown that in the wild male platypus live for about 5-6 years, while females can survive for about 8-10 years. One male survived for 17 years in captivity, but this appears to be an exception.

Swimming

Platypus swim by using alternate strokes of their webbed fore-limbs while the hind limbs are held close to the body. The hind limbs and tail are generally used as rudders and brakes. When swimming, platypus create 'bow-waves' and diving animals roll porpoise-like beneath the surface.

Food and Feeding
Platypus usually emerge from their burrows in the late afternoon or early evening and begin foraging for food. This activity is often interspersed with grooming and scratching. Although the platypus has exceptional vision and hearing above water, it closes its eyes and ears before diving.

Prey is located by means of sensory systems within the duck-like bill. This extraordinary structure is covered in numerous perforations which open into sensory organs that not only respond to touch but also to minute electrical currents emitted by tiny muscle movements of their prey. The platypus is the only mammal known to use electro-location to detect its prey. Platypus spend up to10-12 hours a day diving and foraging for food, returning to the surface every 30 to 60 seconds to consume food collected and to breath. Appearances at the surface are generally short and last only about 10 to 30 seconds.

The food of the playtpus includes invertebrates such as caddis, mayfly and dragonfly larvae, freshwater shrimps, crayfish and earthworms. Food is usually collected at the bottom of a lake or river bed and stored in cheek pouches until the platypus surfaces. It is then ground by horny grinding plates at the base of the bill before being swallowed. Platypus consume approximately 17% to 23% of their body weight each day, depending on air temperature and season. Fat reserves are stored in the tail and are drawn upon when conditions are poor and food is scarce.
[Platypus Observations: Catching Fish]

Burrows and Nesting
During the warmer daylight hours platypus tend to rest and sleep in burrows, sometimes moving among several burrows during a 24-hour period. Often a burrow is shared with other individuals. Burrows are found in river banks and are generally about 2 to 8 metres long. They may have more than one entrance, which are usually located just above the surface of the water, often amongst tree roots. Nesting burrows are usually much longer and more complex, up to more than 25 metres long, and can have numerous side branches ending in chambers. Nesting chambers are about 25-35 centimetres across and are filled with wet leaves, grasses and reed stems. These materials are thought to provide stable humidity levels for incubation of the eggs.
[Platypus Observations: Collecting Nesting Material]

Egg Laying and Raising of Young
In the tropics, breeding activity starts in late winter to early spring. Breeding success depends on weather conditions prevailing at the time. Females retire to their nesting burrows during August and September to commence egg laying. To prevent intrusion by other platypus and also predators, the females block the entrance with a leafy plug.

Usually two, but occassionally three, soft-shelled eggs are laid. These stick together, and are then incubated on a 'brood-patch' on the female's belly and held in place by the tail. Incubation is thought to take about ten days and when the young hatch they take milk from the mother by way of 'milk patches' on the female's belly.

Young platypus leave the burrow and become independent at about 3-4 months of age. It appears that juveniles are often forced to disperse to find their own territories because of competition with adults for food and burrows. This dispersal period can be a critical time for the young animals, often resulting in high mortality if they are unsuccessful at establishing a territory.

Venomous Spurs
Adult male platypus have a horny venomous spur about 12 millimetres long, on the inside of each hind foot. This is connected to a gland in the thigh which produces venom capable of causing excruciating pain and incapacity in humans. The venom appears to be at its most toxic during the breeding season. Both young male and female platypus emerge from the egg with a spur, but this does not develop in the juvenile females and is shed after about nine months. In juvenile males the spur continues to grow and is fully developed at about 18 months. It is assumed that the spur is used in defence or to attain dominance in the platypus' social system.

Platypus Predators
Platypus are eaten by a variety of predators including spotted-tailed quoll, dingo, feral cat, monitor lizards, water rat, pythons, crocodile, eels and possibly other large fish. There may also be avian predators such as owls or eagles. Platypus are also occasionally taken on worm-baited fishing lines and become entangled in discarded mesh and nylon.
[Platypus Observations: Escaping an Owl, Eaten by Eagles?, Collared by Accident]

Platypus Conservation
What kind of habitat does the platypus require in order to maintain a healthy population? Research from the less tropical areas of Australia suggest that platypus are affected by the clearance of vegetation from streambanks and by channelization of stream beds. In addition to causing instability for burrow construction, the loss of vegetation may alter the microhabitats of a stream, therefore decreasing diversity, abundance, and availability of prey. Other factors that have been associated with population declines are strong changes in pH, high water temperatures, and increased amounts of garbage in the stream. Most of the scientific studies conducted to date have been carried out in New South Wales and Tasmania, and have compared degraded or urbanized watersheds to less degraded watersheds. However, current research efforts are now attempting to establish clearer correlations between habitat changes and platypus populations to determine possible cause and effect relationships. To date, there has been little direct platypus research done within the Wet Tropics Region.
[Platypus Observations: Collared by Accident]