Previously known as the Long-tailed Field Mouse, the Wood Mouse Apodemus sylvaticus is the commonest mouse in Britain. It may be identified by its large ears and bright bulging eyes. Its head and body are 81-103mm long, with a tail of 82-95 mm. The upper sides are dark brown shading to yellowish brown on the sides. The underside is greyish white with sometimes a yellowish spot on the chest. This spot varies in size but is never so big that it extends to the brown of the upper sides to form a band across the chest as in the Yellow-necked Mouse Apodemus flavicollis. The tail is dark above, pale on the underside and only sparingly haired. When handled it is easy to strip the skin from the tail leaving the vertebrae which dry and eventually break off. Mice should therefore be held by the scruff of the neck and only steadied by the base of the tail. Juveniles are a greyer brown above and greyish white below and could be mistaken for House Mice Mus domesticus especially when seen inside buildings. Various colour variations have been found as well as piebald and semi-hairless individuals. In our region, jet black Wood Mice have been found at Cowpen Bewley Woodland Park, a completely cream coloured individual at Hartburn, and a sandy-brown individual on the dunes at Lindisfarne. It was postulated that the latter might possibly be a local adaptation to its environment; however, Flowerdew and Tattersall (in Harris and Yalden, 2008) point out that Wood Mice can become paler and sandy coloured with age.
It is distributed all over Britain with distinct island forms developed where isolated from the mainland. The British population is thought to have developed from two roots, one originating in France, which repopulated Britain as the ice retreated, and the other from Scandinavia. These latter may have been introduced in hay brought by the Vikings and now populate many of the islands of north and west Scotland (Flowerdew and Tattersall in Harris and Yalden, 2008). There are unlikely to be any altitudinal limits to its distribution in the North East as it has been recorded on the summit of Ben Nevis (Perry, 1981).
Wood Mice are principally nocturnal woodland animals but are very adaptable in their habitat use and inhabit woodlands, gardens, grassland, arable land and even sand dunes and heather moorland, though above the tree line numbers decline except where cover is available, for example dry stone walls. Habitat use and home range size varies with the type of habitat and the food supply available within that habitat. Activity also varies; mice in sand dunes have to work harder for a living than those in a corn field. Their burrow systems are sometimes complicated and are probably occupied by successive generations.
They are very opportunistic as regards food. Their diet consists of seeds, buds, stems, nuts and fungi as well as invertebrates such as caterpillars, centipedes and worms. Exceptionally they have been known to eat vertebrates such as frogs and to feed, and even nest, in beehives, where they have also been found stung to death and encased in wax (Burton, 1968). For those living in sand dunes invertebrates are the main food source. Wood Mice climb well and often use old birds’ nests as stores or feeding platforms. This habit of storing food means that when, as often happens, they collect newly sown peas or bulbs from gardens the damage is greater than would be expected from so small an animal, though these stores are sometimes the work of more than one animal (Burton 1968).
Wood Mice do not usually live for more than one winter. They breed throughout the summer, having several litters of from two to nine young, but normally not during winter when the older adults usually disappear from the population. However, winter breeding can occur if unusually large reserves of food can be utilised. One item of behaviour worth mentioning is that when disturbed while feeding the young, females will leave the nest with the young still holding on to the nipples.
Some years ago a study was carried out on small mammals in Hamsterley Forest by a South American graduate, F. Fernadez, for a PhD at Durham University. He marked Wood Mice in a clear felled area at High Acton Currick. A farmer’s wife at Mayland caught a ringed mouse and sent it to Gordon Simpson of the Forestry Commission who was helping in the study. The mouse had travelled a distance of 5.1 km. Fernandez retrapped another Wood Mouse, west of the forest, which had travelled over 1.75 km (Gordon Simpson, pers. comm., 2012).
Although a good candidate for the most ubiquitous mammal in the region, it is also one of the most overlooked. One of the few historical mentions is by Mennell and Perkins (1864) who merely state that “This species is abundant throughout our district.” Similarly The Victoria History of the County of Durham (Page, 1905) sums them up as “common”. Our record maps show the effect of under-recording very well. The post-2000 map shows the collection of records around the main centres of human population. The pre-2000 map however shows the results of concentrated trapping and recording in and around Forestry Commission lands during the late 1980s and the 1990s. It is probable that the same effect could be obtained in any area within the region if sufficient trapping effort was put into it.
Written by Don Griss (last updated Nov 12)