I was in Dimboola last week collecting water samples from the Wimmera River (using eDNA to investigate carp distribution and abundance to improve control efforts). While I was parked next to the river preparing some equipment early in the morning, I noticed a streamlined shape swimming across the river, creating a distinctive V-shaped bow wave. I only got a fairly brief glimpse, the early morning sun was in my eyes and reflecting off the water, and the animal was moving quite quickly before disappearing in the opposite bank. The shape had a low profile in the water and was furred so it clearly wasn’t one of the many ducks in the area. My immediate reaction was ‘platypus’ and got very excited as platypuses haven’t been recorded in the area for ~30years! After my initial excitement, I tried to reflect on what I had briefly seen. I’m now fairly convinced that it was a rakali (water rat) due to its behaviour and swimming style (travelling across the river from bank to bank, several small dives as it swam) although I couldn’t see the rakali’s distinctive white tail tip.

The point is that it can sometimes be extremely difficult to confidently identify a species, even one as unique as a platypus, from a brief glimpse, at a distance, often in poor light, and sometimes partially obscured. Even as an experienced platypus ecologist who has seen 100’s of platypuses, I can’t always be 100% sure that it was/wasn’t a platypus. And here is the dilemma – do I not bother to report the platypus sighting described above because I can’t be absolutely certain (possible false negative)? Or do I report it and risk giving potentially false information (possible false positive)? Because, in this instance, if it WAS a platypus, this is a really important piece of information as platypuses are thought to have disappeared from this area many years ago.

This is the strength of citizen science. Citizen science is a numbers game. Firstly because there can be so many eyes out there looking for things but also because the data can be self-affirming. It is easy to discount a single anomalous sighting of a species as misidentification, false data, or a temporary vagrant. But if 5 people report a species in the same area, we can have reasonable confidence that it is present. The more people that report the same thing, the more confidence we have about the data. This makes every sighting valuable. So please continue to post your platypus sightings to platypusSPOT, even if you’re not completely sure that it was a platypus (that’s what the comments section is for). Hopefully, you will get a better look next time, or someone else will confirm your sighting. It’s all about the numbers.