Make your way down to a quiet area of your closest river during dawn and if you sit quiet and have enough luck on your side, you may catch a glimpse of an otter. The otter population has been on the rise since major conservation efforts such as reintroduction and beneficial riverside management practices have been put in place. The species was given protection within the Wildlife and Countryside Act (1981) as the population decreased drastically during the use of organo-chlorine pesticides. Since the government banned the use of organo-chlorine pesticides in the 1970’s, the otter population which had previously been sparsely distributed has become more widespread and there are now sightings in every county, with some sightings recorded in urban areas – an unusual choice of habitat for such a shy creature.
The otter is a member of the Mustelidae family, members of which are referred to as mustelids. Other British mustelids include badgers, stoats, polecats and pine martens to name a few. The otter is narrow bodied, on average 60-80 cm in length, and is brown furred, although usually paler on it’s underside. Other distinctive features are it’s long tail (usually around 35 cm long) and it’s webbed feet making it a good swimmer in it’s semi-aquatic environment. Otters are not social creatures, and will only interact with other otters when they want to mate. They hunt for fish, amphibians and crustaceans in solidarity within their 20 kilometre stretch of territory. They mark their territory with their faeces, which is also referred to as spraint. Otter spraint can be identified by it’s powerful musky smell (sometimes likened to jasmine tea!) and often contains the bones of fish and amphibians. Otters tend to place their spraints in prominent areas so next time you’re walking by the river keep an eye (and your nose!) out for them. Spraints are usually black and slimy in appearance and range from 3 – 10 cms in length.
Otters will only inhabit areas of clean water where there is an abundance of prey items, and hence the increase in otter population throughout the UK is a sign that Britain’s waterways are the cleanest they have been since the Industrial revolution. If an otter finds a suitable habitat and marks it territory, it will create several areas along its territory called holts. Holts are usually above ground on the riverbank, and can be identified due to the presence of spraint, flat patches of earth where otters lay during the day and you may also see a “slide” down into the river made out of the river bank, so otters can make a quick escape if they are threatened. Holts are usually built within dense vegetation or other areas with sufficient cover.
As otters are quite hard to spot, mammalogists tend to estimate otter populations within surveys based on spraint density within a given area and sometimes from the presence of tracks. Otter tracks are similar in size and shape to dog and fox footprints, but otters leave five toe-prints and sometimes the webs between their toes may be spotted in the footprint.
Despite their big comeback, otters are still considered to be “Near Threatened” on the IUCN Red List and so conservation efforts must remain in practice before we can be sure the otter is well established within the British Isles again. Due to it’s protection, it is important that if you feel inspired to go out and search for otters you remain quiet and respectful to prevent disturbance.
That’s it for this month, suggestions on which mammal to cover next month are welcome.
Danni
Images in this post have be reused under the Creative Commons Licence.
Image Credits: Otters by Peter Trimmings; Spraint by Sarah D; Tracks by Helge Schulz
J & D Science 