All about otters

Did you know that river otters were extinct in Hertfordshire by the 1970s? Here are eight more facts to feed your otter knowledge.

Did you know that river otters:

...are bigger than you might think. Males weigh about 10kg and females about 7kg. They measure up to 120cm from nose to tail. fish, crayfish , frogs and birds.

...make their natural homes - called holts, dens or hovers - in underground cavities below riverside trees. Artificial holts are sometimes made from logs and small branches to encourage otters to breed in areas where their numbers are low.

...are mostly nocturnal - choosing to hunt and to travel by night.

...produce one litter of cubs each year - with two to three cubs in each litter. They are weaned after three months but will remain with their mother for up to a year.

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...have an average lifespan of three to five years - relatively short for a medium-sized mammal.

...mark their territory with a soft, musky smelling dropping - or spraint - which they leave on prominent riverside places. Spraints have a distinctive smell which is likened to a mixture of fish and jasmine tea leaves. A male otter can have a hunting territory of approximately 26 miles.

...were extinct in Hertfordshire by the 1970s due to a combination of hunting and persecution, river pollution and a loss of suitable habitat. Following local improvements, six animals were released in the county in 1991. Sightings and signs of otters have been made in Hitchin, Berkhamsted, Rickmansworth, Denham and throughout the Lee Valley.

A special biodiversity action plan is directing conservation work for otters in Hertfordshire. Herts and Middlesex Wildlife Trusts is working actively with its partners to deliver this plan.