Shrink­ing of the shrew

Rossendale Free Press - - Wildlife - ALAN WRIGHT The Wildlife Trust of Lan­cashire, Manch­ester and North Mersey­side To be­come a mem­ber of the Trust go to the web­site at­lanc­swt.org. uk or call 01772 324129. For more in­for­ma­tion about Cheshire Wildlife Trust call 01948 820728 or go to cheshire

WIN­TER is com­ing and it’s a good time to snug­gle into a warm place and shrink your brain.

Ap­par­ently, that’s what shrews do in the win­ter. It prob­a­bly seems that it hap­pens to one or two of us hu­mans too – if Black Eye Fri­day (the one be­fore Christ­mas) is any­thing to go by.

Se­ri­ously, it has now been proven that shrews do ac­tu­ally make their skulls smaller as win­ter ap­proaches and it’s even got a name – ‘Dehnel’s Phe­nom­e­non’.

The poor lit­tle things do not hi­ber­nate and there is no chance for them to hop off to spend sum­mer some­where warmer, so they need to take ac­tion.

It seems that by shrink­ing an or­gan you will use less en­ergy, so the skull and brain shrink in au­tumn and grow back to nor­mal warm-weather size in spring.

Shrews are pretty cool lit­tle fel­lows, us­ing echolo­ca­tion to find their way around. This is the same method used by bats where they let out a sound and lis­ten for it com­ing back, to work out if some­thing is in the way.

They also let out a strong smell to de­ter the cats that might be try­ing to gob­ble them up.

I have been out on a cou­ple of small mam­mal trap­ping ex­pe­di­tions, where we cap­ture the lit­tle guys and gals in hu­mane traps, record their ex­is­tence, check on their health and then set them free in the same area. We tend to get voles, mice and some shrews, all very ex­cit­ing.

There are three types of shrew in our area – the wa­ter shrew, the com­mon shrew and the pygmy shrew. Shrews have long, pointed snouts, small ears and tiny eyes, and must eat ev­ery cou­ple of hours. They are likely to be seen or heard for­ag­ing for food dur­ing the day. Shrews only eat in­sects.

The wa­ter shrew is the dark­est and the largest of the three. It has dark fur with a pale un­der­side and is be­tween 7cm and 10cm long. It is semi­aquatic and likes to live on the banks of clear, fast-flow­ing streams and rivers. Its main food source is fresh­wa­ter shrimps, wa­ter skaters and cad­dis lar­vae.

The com­mon shrew is be­tween 6cm and 9cm with a yel­low-brown stripe di­vid­ing its brown fur from its grey-white un­der­side.

It lives al­most any­where but is par­tic­u­larly found in hedgerows, scrub, grasses and wood­land.

The pygmy shrew has the long­est tail and the short­est body of the three. Its body length ranges be­tween 5cm and 6cm and its tail can grow to 70 per cent of this length. It is the same colour as the com­mon shrew, without the yel­low-brown stripe di­vid­ing the up­per and lower fur.

The pygmy shrew is usu­ally found in rough grass­land. You may be lucky enough to see one of them dash­ing off from a path as you wan­der through the coun­try­side.

The brain-shrink­ing re­search is by Javier Lázaro, from the Max Planck In­sti­tute for Or­nithol­ogy.

Pic: Neil Wy­att

Com­mon shrew

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