Platypus reproduction
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.
Breeding season
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.
Size
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.
Life span
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 sounds
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.
Predators
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, goannas and Australian water-rats 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.
Disease
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.