Platypus are most often observed near dawn or dusk,
although the animals are also sometimes seen in the middle of the day, particularly
along waterways where the animals are relatively abundant.
Males and females are both dark brown in colour, with
lighter underparts and a small white spot just in front of the eye. The
animals are surprisingly small - approximately 40 to 60 centimetres in length.
They float very low in the water, with a slightly higher profile marking
the location of their head and rump. When viewed at a distance from the bank,
they can bear quite a strong resemblance to a floating stick - and hence
are often first recognised by the conspicuous bow wave created as they paddle
along the surface.
While platypus sometimes swim strongly in one direction,
more often they dive and resurface in a leisurely manner as they feed - generally
popping up again within 25 metres of the point where they dived. When foraging,
platypus typically remain underwater for less than a minute before returning
to the surface to chew their food and sometimes to groom (usually by scratching
with a hind foot).
Platypus dives usually create a very distinctive circular
ripple pattern. This sometimes has a small number of bubbles in the centre,
caused by pockets of air being forced from their double layer of fur.
When alarmed, a platypus will "splash-dive", making
a relatively loud single or double splashing noise as the animal dives abruptly.
Normal "duck-dives" for food are much quieter, sometimes (but not always)
producing an audible "plop".
Australian Water-rats can easily
be mistaken for platypus, especially if an animal is seen only briefly.
At a distance of more than 20 metres, it can be very difficult to tell the
two species apart in the water. The thin, white-tipped tail of the water-rat
is the most obvious way to distinguish it from a platypus, which has a flat,
paddle-like tail. Water-rats are also much more likely to be seen out
of the water (feeding on a rock or log or running along the bank) than platypus
are.
Diving ducks (especially musk ducks) and even swimming
tortoises can be mistaken for platypus momentarily, but are usually readily
distinguished upon longer observation.
