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The results of the Cambridgeshire otter survey are in...

Caroline Fitton, of the Wildlife Trust in Cambridgeshire, reveals the findings of an extensive survey.

Earlier in the year a sharp decline of otter numbers in Wales was revealed in a survey led by Cardiff University and Natural Resources Wales.

River pollution undoubtedly plays a large part in this decline, so by contrast it's encouraging to see that the results of the Cambridgeshire otter survey has found that populations across the county remain in healthy numbers.

An otter. Picture: Sarah Lambert (56794771)
An otter. Picture: Sarah Lambert (56794771)

Covering all major watercourses in Cambridgeshire and many smaller ones as well, this latest survey conducted by the Wildlife Trust in Cambridgeshire in collaboration with the Cambridgeshire Mammal Group started in December last year and ran through to the end of February 2022. It was the latest in a repeat of surveys that have taken place every five years since 1992.

A total of 292 sites were visited by 50 surveyors - trust staff and volunteers, members of the Cambridgeshire Mammal Group, the Environment Agency and the Middle Level Commissioners - who all received training in the methodology of the survey.

It's all about spraint . . . the dignified, delicate word given to otter droppings - seemingly the only mammal to have its own dedicated dropping term - and knowing where to find it.

Canny otters communicate and convey messages in their droppings and they have worked out that this lasts longer under cover, so bridges provide an ideal place for this calling card. With a distinctive smell, similar to jasmine tea but fishy when fresh, every spraint tells a story with a specific signature scent unique to each individual which contains and conveys information - whether male or female, if in season, etc. Prominent places generally make good places for spraint: on ledges, bricks or rocks, and sometimes they may scrape up earth to create their own platform.

Another clue is tracks - otter footprints are asymmetric, ranging in size between 40-80mm and normally showing only four toes even though they have five, and the webbing between the toes also doesn’t usually show.

An otter. Picture Sarah Lambert (56794775)
An otter. Picture Sarah Lambert (56794775)

Those lucky enough to see them may also hear the distinctive series of squeaks and whistles they make, though these are more normally heard at night. The surveyors scoured under bridges, up rivers, down streams, next to lakes, in fenland ditches - along any likely watercourse.

As a bi-product the surveyors also recorded additional sightings or signs of plenty of other species which included badger, bank vole, barn owl, blackbird, common snipe, cormorant, crane, European eel, fallow deer, fox, greenfinch, grey heron, grey wagtail, kingfisher, little grebe, little owl, mallard, mole, moorhen, muntjac deer, mute swan, rabbit, red kite, robin, roe deer, skylark, wood pigeon, wren and whooper swan. A snake skin and a belemnite fossil were also found.

All of these records were sent to the Cambridgeshire and Peterborough Environmental Records Centre along with data on otter, water vole, brown rat and American mink.

The charismatic, mercurial European otter has been here for millions of years. A member of the Mustelid family, which also includes the badger, mink, weasels, stoats, martens and polecats, it is the only truly semi-aquatic member of the weasel family.

The average otter is 1-1.3 metres in length, and weighs up to 9kg, with a diet consisting of roughly 80 per cent fish, but if fish are in short supply they will prey upon birds, mammals and frogs.

Their gestation period is nine weeks and they can breed at any time of the year, although this would usually take place in spring, with two or three cubs weighing no more than 40g. Cubs are not born natural swimmers, and very often adults will force their young into the water for their first swimming lesson. With an acute sense of smell, hearing and eyesight, the otter's eyes are placed at the top of the head, so it can remain alert whilst the rest of the body is underwater.

The Mammal Society, Environment Agency and Natural England, with support from a number of water companies, will be initiating the sixth national otter survey of England later this year – registration to take part is by 31 July 31 at mammal.org.uk/national-otter-survey/

Visit wildlifebcn.org/news/cambridgeshire-otter-survey-results-2022 and cambsmammalgroup.org.uk.

River Cam bat punt safaris

A bat punt on the River Cam. Picture: Wildlife Trust (56794769)
A bat punt on the River Cam. Picture: Wildlife Trust (56794769)

ln the dusk, something's stirring on the River Cam on Friday and Saturday evenings from now until September. Hand-held detectors in hand, punters clamber aboard a punt to be chauffeured in the fading light down towards Grantchester Meadows.

As dusk falls echoey squeals and clicks start to emit from the hand-held machines - the echolocation of bats.

A Wildlife Trust guide will interpret the sound to reveal which of the 12 bat species that reside in the county it may be.

A bat punt on the River Cam. Picture: Wildlife Trust (56794777)
A bat punt on the River Cam. Picture: Wildlife Trust (56794777)

These summer eve bat punts help to dispel myths about bats - the UK's only flying mammals. These astonishing tiny creatures are to be revered, not feared. . .

In conjunction with Scudamore's punt company, half of the ticket price comes to the trust, so every trip helps support local wildlife.

Visit wildlifebcn.org/bat-punts.

Read more from the Wildlife Trust BCN

Helping nature’s recovery: Cambridge Nature Network, Cambridge Nature Festival and 30 Days Wild

The butterflies of Cambridgeshire: past, present and future

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