Shrinking of the shrew
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.
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