Of mice and cat

It is often assumed that the mouse caught in the house is a house mouse. In fact it could easily be a wood mouse, especially in winter when they come into our homes looking for warm lodgings and plentiful cuisine.

The wood mouse has a number of features to distinguish it from its relatives. It has a pale grey or white underside with a distinct demarcation from the dark fur above. This is lacking in the house mouse. Other distinctions include the wood mouse having a smooth tail and large bulging eyes. On its chest is a yellow longitudinal mark which can be inconspicuous. If this yellow mark extends right across the chest, you have found a yellow-necked mouse, but I fear this is unlikely. Should you be so lucky, please let me or the Trust know.

A good reason for expecting to see a wood mouse rather than its more dowdy cousin is their relative numbers. The latest estimate of house mice in England is 4.5 million, whereas wood mice numbers are about four times this. Yellow-necked mice have been estimated at 600,000, with a distribution mainly in eastern and south-eastern England, with only occasional records from the South-West. Even allowing for under-recording because of confusion with the wood mouse, the West has a low population.

While researching this article, our cat must have sneaked a look at my books because he decided to conduct his own survey. That evening he went out the back through the cat flap to return with a live, apparently uninjured wood mouse. We effected a rescue after a chase round the dining room and released it out the front. Having lost his plaything, the disappointed cat went out again, to return with a second victim. Another chase, another rescue. A third expedition produced a mouse which had a swelling in the middle of its tail. More action for the rescue team.

The next evening our macho pet came in with another prize. That swelling on its tail was the least of the mouseís problems. The following afternoon the cat was seen playing with a small mammal in the garden. As I have said, that swelling was the least of its problems. Next morning we found a dead mouse in the kitchen. Wrong! No swelling on the tail.

All this is very unusual. Most of the catch of the cat is voles. Mice figure only occasionally. As for his survey, it is not valid. His sample is too small. Did he search all possible habitats? All this raises questions. What is the distribution of small animals and numbers in an area? How do numbers vary with area, season and from year to year? Is there a trend of decline or increase and, if so, why? What is the effect on other wildlife such as birds of prey?

Clearly, investigating small mammal populations has many problems and needs special techniques to find answers. Trapping can be used for shrews (with a licence), voles and mice. Harvest mice cannot be trapped in the usual way and present a particular challenge. A national survey using tennis balls on canes has met with poor success. Dormice, which, by the way, are not mice, can be surveyed using nest boxes (licence needed). There are also the larger animals like badgers, stoats, weasels, foxes and even deer.

On the subject of dormice, that reminds me of something I soon learned when I became interested in mammals. It is dangerous to be dogmatic about the behaviour of a species or, to put it another way, to draw conclusions from too few observations. I have been monitoring 50 dormouse boxes as part of a national scheme. For four years, July and August always proved to be a fruitless period with no animals, whereas up to a dozen have been present in October. This is the month the Mammal Society uses to compare numbers in all sites. This year I have had dormice in boxes in July and August and was looking forward to a bumper crop in October. What did I get? One! Oh well, thatís mammals!

Ron Evenden

The author will be delighted to hear from anyone who is interested in joining the Trustís new Mammal Group - see contacts on page 2.

Wood mouse

Wood mouse - surveyors (and cats) may note the distinct demarcation between the pale underside and darker fur. Photo: Ron Evenden

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