Otter Ecology & Field Signs, Pt 1

Otters can be very difficult to watch and photograph, but its more than possible with a little time looking for the right signs, and a bucket full of patience !

Otters are fascinating and elusive creatures that are found throughout the UK. Whilst they are thankfully much more common than they were, they can still be difficult to spot due to their largely nocturnal and semi-aquatic nature. However, with a little bit of knowledge and some careful searching for clues, it is possible to identify the presence of Otters in an area by looking for field signs.

One of the most obvious field signs of Otters is their droppings, which are known as spraint. Spraint has a distinctive fishy smell and is often found on prominent features such as rocks or logs close to water. When fresh it is typically dark in colour and has a spiky, tarry appearance due to the high content of fish bones and scales. As the spraint ages it becomes lighter in colour and more crumbly, although it never really looses it’s fishy smell. Spraint can be a reliable field sign of otters because they are relatively consistent in their defecation habits and tend to use the same sites repeatedly. Good places to search for spraint are under bridges, on prominent rocks, logs, or boulders that stick up above the waterflow, or on small areas of headland that stick out into the watercourse.

This spraint was found on a concrete culvert next to a small stream. You can see the remains of fishbones, and the grey colour tells you this is not recent.

Another field sign of Otters you can search for are their footprints, which can be found on muddy banks or in shallow water. Otter footprints are around the same size as a medium pet Dog print (6.5-9cm long), however Otters have five toes, whereas Dogs have just 4. Otter prints can show webbing between the toes and sometimes claws, but this is very dependent on the substrate, and the speed the Otter is moving at. Otter footprints can be used to determine the size and sex of the animal, as males tend to have larger feet than females, but remember in both sexes the rear foot is bigger than the front one so make sure you are comparing like for like. Great places to look for prints are at the waters edge, particularly where there is a kink in the river and an Otter may coem out of the water and take a direct route across a headland or piece of land that sticks out into the water course. Mud and sand are the easiest places to find prints.

The Wildlife Nomad and Gloucestershire Otter Watch are happy to provide this quick guide to Otter prints (right click and save as JPG).

Otter and Mink prints are similar but un-suprisingly American Mink prints are much smaller. Mink are related to Otters (both being Mustelids, like Badgers, Martens, Polecats, Weasels and Stoats) but their habits are quite different with around 80% of Otters diet coming from fish, and only around 35-40% of a Mink’s diet being fish. You can clearly see the differences in their prints below.

For more information about Otters, you can join one of our Ecology and Survey Days, by clicking “courses” at the top of this page.

Otters also leave marks on vegetation, such as grass or reeds, when they enter or exit the water. Look for tunnel like structures, about 20cm in diameter, that have been formed as an Otter has repeatedly pushed through long grass and other vegetation leading to or from the water. These tunnels through the plants may lead to an obvious point of entry into the water, or like in the image below lead to an area underneath the plants where they can hide themselves away.

Typical of Otters where there is plenty of vegetation, this “tunnel entrance” is approximately 20cm across and is not dug into the earth of the bank, but leads to an area behind the reeds where they can hide.

Often where the banks are steep and they are frequently used to get in and out of the water, you will find an Otter “slide” where the mud of the bank is smooth. Look for prints to confirm you suspicions. Slides can be useful for tracking the movement of Otters and are a good point to set a camera trap to confirm the animals presence.

Otters also crush and mark vegetation when they drag larger prey items out of the water to eat them. Smaller prey will often be eaten in the water, but larger or more difficult fish are brought on to the bank rather than struggle with them in the water. Remains of prey they have consumed on the bankside are good for confirming what species they are eating. Also look around structures where eels and other fish congregate, such as piers and sunken boats. Otters will hunt close to these structures, albeit possibly after dark.

In addition to these physical field signs, Otters can also be detected by their vocalizations. Otters are known for their distinctive "whistling" call, which is often heard at dawn or dusk. They can also make a range of other vocalizations, including chirps, clicks, and purrs, which can be heard during social interactions or when they are in distress. By listening for these vocalizations, it is possible to determine the presence of Otters in an area and learn more about their numbers. I have on several occasions heard Otters calling to each other and they have been just a few feet from me, but I have been unable to see them as they remain deep in cover or under the edge of the bank. Little is more from frustrating than after hours of waiting hearing an Otter, but not being able to see it!

While it can be difficult to spot Otters in the wild, there are a number of steps that can be taken to increase your chances of photographing these fascinating animals. For example, visiting areas where Otters are known to be present at dawn (when Dog walkers, families and joggers are not so prevalent), particularly when it’s cold or raining I have found to be the best . Being well camouflaged, and sat back from the water will increase your chances of seeing Otters, and be prepared for a long wait :-), I can sit for hours without seeing a thing! I rarely use a tripod as I like to be mobile and as stealthy as possible.

Where disturbance from humans and Dogs is minimal, Otters can be seen in the open in daylight, and can be photographed hunting. Every Otter is different but they will typically dive for between 20 and 30 seconds when after fish. If you spot an Otter the best thing to do is to freeze, and once they dive count how many seconds they are submerged for. I like to do this a couple of times (to see how long they are staying under for on average) and then on the third or forth dive, move whilst they are underwater. This allows you to get yourself in to an advantageous position to photograph them once they come back to the surface. REMEMBER AT ALL TIMES THAT THE ANIMALS SAFETY AND WELL BEING IS OF THE UPMOST IMPORTANCE. Do not chase an Otter or get too close, and remember they are hunting to survive, don’t do anything to jeopardise their chances of success.

Getting to know how long the Otter will dive for is vital to getting yourself in a position to make the most of your shooting opportunity when it comes back to the surface.

In terms of their typical lifespan and monthly activity, Otters have a relatively short lifespan for their size, with a maximum of about 10 years in the wild (most making less than 4 years). They are active year-round, but their activity levels can vary depending on the season and the availability of food. I would suggest Winter is a good time to watch inland Otters in Southern England, as whilst during the Spring and Summer months, Otters are more active, so are humans and Otters tend to lessen activity when there is risk of disturbance.

Next month, in Part 2 of this series, we will look at Otter breeding, nesting and parenting behaviour.

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