Wednesday, 1 January 2014

Naming of the shrew

The other day I was forwarded a photograph of a shrew that had been found dead near to a pond, prompting the sender to question whether or not they had found a water shrew. It turned out that the shrew in question was an unfortunate common shrew. The question of the shrew’s identity reminded me that the names that we give to species are not necessarily helpful when it comes to their identification. Take the common redpoll for instance. This is a species that is actually rather uncommon in Britain; the redpoll that we see ‘commonly’ is the lesser redpoll and the whole situation is further complicated by the fact that we usually just refer to this delightful little finch by the name ‘redpoll’.

In the case of the water shrew there is, at least, an association with waterside habitats and this small mammal shows a number of adaptations to its aquatic habits. The tail of the water shrew has a keel of stiff hairs running along its underside and the feet also carry these as a fringe on their margins, both of which help the shrew to move through the water. Water shrew populations appear to be largest in those habitats associated with water, including rivers, ditches and wet meadows, with watercress beds proving a particular stronghold for the species in the south of the country. However, this large shrew can also be found in other habitats and often at some distance from any waterbody. I have, for example, trapped them in the middle of a young sweet chestnut plantation and a gamekeeper friend occasionally encountered them in arable hedgerows close to the downs.

Our other mainland shrews – the common shrew and the pygmy shrew – often occur in damp habitats (both species have been caught in traps set at watercress beds), with the latter species fairly regularly associated with particularly wet habitats. This underlines that you should never jump to an identification purely based on where you found the bird or animal. Habitat can be important, particularly for certain plants and fungi, but you should always use it alongside other characteristics and avoiding jumping to an incorrect conclusion about an identification.

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