Otter on Shetland © James Warwick / Getty
1 Both males and females hold territories, although male territories tend to be slightly larger.
2 Their droppings are known as spraints and can be identified by an odour that is said to range from musky mown hay to jasmine tea to rotting fish.
3 Otters have their cubs in underground dens called holts, which they dig themselves. They will also use hollows under trees or old rabbit holes.
4 Otters have webbed feet, dense fur to keep them warm and can close their ears and nose when swimming. Bubbles of air trapped in their fur give them a silvery appearance underwater.
5 They are members of the Mustelidae family, a group that also includes badgers, pine martens, polecats and weasels.
6 Coastal otters also require a source of fresh water to clean their fur in order to retain its insulating properties.
European otter on the Isle of Mull, Scotland © Paul Hobson
7 The mustelid is active by day or night, though generally more nocturnal on fresh waters.
8 Back in every English county since 2011 and seen even on urban rivers, the otter is at last reclaiming lowland wetlands far beyond its Scottish and Welsh strongholds.
European otter in Thetford, Norfolk © David Tipling
9 Common otter numbers decreased drastically throughout the UK in the late 1950s and early 1960s. Habitat loss and pollution played a major part in the decline.