A Notter - When is an otter not an otter?

 Species identification can be a minefield, and one of the most common complications regards the differences between a mink and an otter.

In actual fact, once you have seen an otter, it is clear what it is, and the difference between it and a mink is pretty clear, but it is rare to see both together, and weather conditions can make things difficult.

Earlier this month otter cam recorded some great clips of both species, and I thought it would make a nice teachable moment.

Mink and Otters are both mustelids and exhibit similar body shapes. They are also both aquatic species and are found in similar habitats.

First of all, look at the video clip below:

It shows an animal emerging from water and then scouting around a little. It is definitely a mustelid, and aquatic. We can rule out Weasel due to its size and the lack of a white/cream chest and underside like a Stoat. Its back doesn't arch as much as a Polecat, and it's the wrong colour for a Pine Marten.

It's either a Mink or an Otter. What do you think?

What about the next clip?

This clip shows two animals running across the screen before entering the water. Look at the tail and muzzle.

Now that you have seen both species in the same location, you should be able to identify which is which.

Clip 1 shows a North American Mink, and Clip 2 shows a pair of Otters.

It's understandable to think that the individual in clip one is an otter. It is quite a large Mink and obviously a similar colouration to an otter, but note the following telltale signs.

The tail - Otter tails are much sleeker and rudderlike. They slim to a point, whereas Minks have broader tails that are a bit fluffier.

The head: Mink have thin heads that are taller than wide, but otters tend to be wider than tall. Eye placement is slightly different, with Mink eyes pointing more forward. 

Ears - Otter ears are much sleeker and do not stick out much from the line of the head, whereas Mink ears seem larger and are more noticeable.

Another key diagnostic feature is how they swim. Sadly, I do not have an image of mink swimming, but they do so in very different ways. Mink are only partially aquatic and not as well adapted. They tend to sit higher in the water and paddle quickly. Otters, when swimming, often only show their heads. They are highly evolved to swim; they are more agile and playful in the water. They use their tails to steer and propel, and will dive much more often.

Otter swimming

If you want to know more, then BBC Wildlife Magazine has a nice article here