Diet
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.
Feeding behaviour
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.
Nocturnal behaviour
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.
Hibernation/torpor
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).