Jan 03 2019

Picking the Bones out of an Otter’s Lunch

Very few of us are lucky enough to have seen a real live otter though they frequently swim, hunt and raise cubs along the River Bovey and its tributaries. They are the apex predator in the food chain of this watery world and, though they have an elusive reputation, will leave us regular clues about where they have been and, if you look closely, what they have been eating.

  Bovey Valley otter – captured on trail camera by Simon Smith

Please excuse the direct approach to getting down to business, but otter droppings are known as ‘spraint’ and they are regularly deposited in a prominent position along the river. Leaving them perched on a protruding rock serves the dual purpose of the disposal of indigestible food waste and warning other creatures of a territorial claim. Spraint has a peculiar, oily smell which is not unpleasant and can even have an unusual sweet aroma. At this point, I have to say that this is probably one of those things that suits only a minority of naturalists but, if Chris Packham can make a career out of studying wild animal poo, then why shouldn’t I have a go too?

  Otter spraint deposited on a rock beside the Becka Brook

I am a big fan of the otter and, every time I’m near a suitable watercourse, I listen out for their calls, look out for their paw prints and keep an eye open for the ‘treasure’ they leave on the rocks along the river. The European Otter (Lutra lutra) is a protected species and disturbance should be kept to a minimum but, when a spraint is found, it can reveal all sorts of information about life on the river without even bothering the animal itself.

  Otter print in gravel beside the River Bovey

Back in March, I found a spraint on a rock, took it home and, without going into too much detail, separated the remaining bone fragments and analysed the contents of the delightful deposit! It was quite interesting. There were fish bones from bullhead and trout, and a few fragments of frog. Quite a variety of tasty morsels.

     Frogs, trout and bullheads all make up the diet of a Bovey otter, Frog bones, trout teeth and bullhead vertebrae

When I found another spraint on the same rock in December, it was a different story. The water levels had been very high for a few days and the opportunistic otter had clearly struggled to find a range of prey and its diet was almost entirely trout. How do we know this? Well, each fragment of crunched up bone that passes through the otter’s digestive system provides a diagnostic clue of whatever is (or was) living in the river. It’s a miniature world that tells the Tales of the Riverbank.

 Trout jaw bones   One spraint contains many bone fragments  

 This tiny ‘atlas’ bone is diagnostic of whether the bones are trout or salmon   The tell-tale ‘porous’ vertebrae of ‘salmonid’ fish

 

by Matt Parkins

Taken from https://eastdartmoorwoods.org/2018/12/28/picking-the-bones-out-of-an-otters-lunch/

 

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