Platypus or Ratypus (sorry!): how to distinguish platypus from rakali
20 January, 2016
You would think identifying a platypus in the wild would be easy. It is one of the most unique and recognisable animals on the planet! Certainly, if you get a good look, it is hard to mistake that iconic bill and wide, paddle-like tail. The problem is that you often only get a quick glimpse, or it’s at a distance, or the light is bad, or (most often) all of the above. It is easy to mistake that vague shape in the water for a stick (hint: sticks travel with the current, platypuses will often hold themselves stationary or move against the flow) or a water bird (hint: water birds have a higher profile in the water with the head and neck projecting vertically, platypuses have a very low flat profile). But perhaps the most common case of mistaken identity is between platypuses and rakali (Australian water rat).
Rakali are a fascinating native rodent that we know relatively little about, despite its widespread occurrence throughout Australia (learn more about rakali here). Rakali are one of only a few Australian mammals adapted to aquatic habitats with dense, waterproof fur and partially webbed hind feet. Its distribution overlaps extensively with the platypus and often occupies the same habitats, sometimes leading to mistaken identity. It can be difficult to tell the two species apart, especially when you only get a brief glimpse or in poor light. Both are furry, similar in size and colour, and sit quite low in the water. The most observable feature to distinguish the two species is the rakali’s long thin tail with a striking white tip compared to the broad, flat tail of the platypus.
Photo credit: Peter Weinstock
More subtle signs include differences in their behaviour and the bow waves created when swimming on the water surface. Platypuses tend to stay on the surface when travelling, creating a long, narrow V-shaped wake. When foraging, platypuses repeatedly dive and surface at intervals of approximately 30-60 seconds in the same area. The wake from a rakali may be subtly wider and more S-shaped due to their more sinusoidal swimming movements. Rakali will often perform short dives while swimming along, resurfacing some distance from where they dived, and taking any prey (insects, crustaceans, molluscs, fish, frogs, even water birds) towards the banks to be consumed where they leave middens behind in favoured feeding spots. While platypuses are rarely seen in marine environments, rakali are commonly found in sheltered coastal bays and estuaries.
Hopefully these tips will help you to distinguish between a platypus and rakali although it can still sometimes be very difficult to be certain. Despite the possibility for mistaken identity, we encourage you to continue to post your platypus sightings to platypusSPOT. You can add any uncertainty in the comments section and hopefully someone else will be able to verify your sighting. That's the strength of citizen science.
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