Seasonality
Platypuses are active all year round, but mostly during twilight and in the night. During day, individuals shelter in a short burrow in bank. The activity patterns of these animals are determined by a number of factors including: locality, human activity, ambient temperatures, day length and food availability.
Feeding and diet
The Platypus feeds mainly during the night on a wide variety of aquatic invertebrates. The average foraging periods last for 10-12 hours per day, and the distances the animals move during this time vary between individuals and their distribution. The animal closes its eyes, ears and nostrils when foraging underwater and its primary sense organ is the bill, equipped with receptors sensitive to pressure, and with electro-receptors. The precise way in which the Platypus uses the bill to detect prey is still unknown, but the bill serves to find and sift small prey from the substrate, while larger prey is taken individually. The Platypus stays underwater for between 30-140 seconds, collecting the invertebrates from the river bottom and storing them in its cheek-pouches. It then chews the food using its horny, grinding plates, while it floats and rests on the water surface.
Diet of the Platypus consists mainly of the benthic invertebrates, particularly the insect larvae. The species also feeds on free-swimming organisms: shrimps, swimming beetles, water bugs and tadpoles, and at times worms, freshwater pea mussels and snails. Occasionally the animals catch cicadas and moths from the water surface. In captivity, the Platypuses are often fed freshwater crayfish (Yabbies).
Other behaviours and adaptations
When swimming, the Platypus presents a low profile, with three small humps (the head, back and tail) visible above the water surface. The swimming action is smooth, and when the Platypus dives the back is arched as the animal plunges underwater, creating a spreading ring. These characteristics coupled with the absence of visible ears distinguish the Platypus from the dog-paddle style of the Water-rat.
Platypuses can swim through fast waters at the speed of around 1 metre per second, but when foraging the speed is closer to 0.4 metres per second. However, the Platpus is not well adapted for walking on land. The limbs are short, heavy and splayed away from the body, and a Platypus uses almost 30% more energy when moving on land, compared to a terrestrial mammal of similar size.
Communication
The Platypus is largely a solitary animal, but several individuals can share the same body of water. The vocalisation has not been recorded in the wild, but captive animals produce a low-pitched growling sounds when disturbed or handled.
Life history cycle
Young Platypuses do not seem to reproduce in their first year of life, instead, both sexes become reproductive in their second year. Still, many females do not breed until they are at least 4 years old. After mating, a female will lay 1-3 eggs (usually 2) following a 21-days gestation period. She then incubates the eggs for possibly 10 days, after which the lactation period lasts for 3-4 months before the young emerge from the burrow. Platypuses are long-lived animals both in captivity and in the wild, living up to approximately 20 years.
Breeding behaviours
The breeding season of the Platypus varies with distribution and within populations. Studies suggest that breeding occurs earliest in Queensland, followed by New South Wales, Victoria and Tasmania. Mating normally takes place between August to October in New South Wales and Victoria, and lactating females were observed between September and March.
The knowledge of the breeding behaviour generally comes from observations of animals in captivity. In winter (when the water is still cold) males initiate mating interactions. Courtship includes aquatic activities such as: rolling sideways together, diving, touching and passing, and the male is also observed grasping a female’s tail with its bill. The behaviour last from less than a minute to over half an hour and is usually repeated over several days.
After mating, a pregnant female builds a nest in a long complex burrow (possibly re-worked by several females in different seasons) in less than a week. She spends further 4-5 days collecting wet nesting material to prevent her eggs and hatchlings from drying out. During the egg incubation period, a female holds the eggs pressed by her tail to her belly, while curled up. She intermittently leaves the burrow, however, much of this aspect of the animal’s life is still unknown. When the young hatch, the female starts secreting milk and the young Platypuses suckle from the two milk patches covered by fur on the female’s abdomen. The female spends most of this time with her young in the burrow, and as the young grow, she increasingly leaves them to forage. Towards the end of the summer the young emerge from the burrow and their fate as young independent animals is still largely unknown.
Conservation status
The Platypus is protected by legislation in all of the states that it occurs in. Individuals cannot be captured or killed, except for scientific research. The Platypus is a common species with very little apparent change in its historical distribution (except in South Australia). However, there is a general lack of knowledge in the species abundance at local catchment levels to predict population trends. The dependence of Platypuses on the established freshwater systems may lead to their decline in future.
Under IUCN the Platypus has been listed as Near Threatened species (year assessed 2014).
Predators
Platypuses spend most of their time in water or their burrow, so it is difficult to determine their predators. There have been anecdotal reports of the species being predated on by crocodiles, goannas, carpet pythons, eagles and large native fish. In addition, it is likely that foxes, and possibly dogs or dingoes kill Platypuses that move on land or in shallow waters.
Platypuses have a number of ectoparasites in the wild, including their own tick species, Ixodes ornithothynchi. The tick is often found around the hind limbs, and in smaller numbers on the front legs and in the body fur. Severe skin ulcers caused by the amphibian fungal infection have been reported in Tasmanian Platypuses in particular. The fungus can be fatal to the animal if it invades other tissues, particularly the lungs.
Danger to humans
Male Platypuses have a calcaneous, sharp spur about 12 millimetres long on each ankle. The spur is connected via a long duct to a gland that produces venom, particularly in the breeding season. The venom can cause severe pain to humans, and although not lethal, the pain caused has been described as excruciating. Swelling rapidly develops around the wound and gradually spreads throughout the affected limb. Information obtained from case histories and anecdotal evidence indicates that the pain develops into a long-lasting hyperalgesia (temporary increased sensitivity to pain) that persists for days or even months. Therefore, if there is a need to handle a Platypus (helping an injured animal for instance), it should always be picked up by the end half of the tail to avoid the spur in case it is a male.
Fossils description
The fossil record for monotremes is poor in comparison to that of other groups of mammals, and until recently little was known about their evolutionary history. Several fossil discoveries since the early 1970s have shed some light on the origins of monotremes. We now know that monotremes were present in Australia during the Mesozoic Era, when Australia was still part of the supercontinent, Gondwana. The fossil evidence suggests that monotremes originated and diversified in the Australian/Antarctic section of Gondwana, and that there was only a single dispersal to South America before the break up of Gondwana.
Four species related to Platypus have been found in fossil deposits from Australia, including a complete skull of Obdurodon dicksoni and an opalised jaw fragment of Steropodon galmani. The latter is 110 million years old and represents one of Australia’s oldest mammals. The only evidence that Platypus ancestors were once present outside Australia came in 1991, when a 61-63 million year old fossil tooth was found in Patagonia, in southern Argentina.
