The Mammal Society

For Evidence Based Conservation

 

Species – Wood Mouse

Wood Mouse – Apodemus sylvaticus

Photo by Samuel Hood
 
Habitat: Urban & gardens, upland & moorland, deciduous woodland, grassland, mixed woodland, heathland, arable land.
 
Description: A small rodent with sandy brown fur (darker towards the spine) with a white/grey underside, protruding eyes, large ears, long tail. Juveniles are greyer overall, still with larger ears, hind feet and tails than house mice.
 
Size: 8.1-10.3cm; tail 7.1-9.5cm
 
Weight: 13-27g.
 
Lifespan: Few adults survive from one summer to the next.
 
Origin & Distribution: Found throughout the British Isles, even on the smaller islands, the wood mouse is our most common and widespread wild rodent. It is an inhabitant mainly of woodland and fields but is highly adaptable and is found in most habitats if not too wet. It is rarely recorded on higher exposed ground with little cover. Wood mice are essentially nocturnal but some individuals may venture out in daylight.
 
Wood mouse distribution (in green), taken from ‘Britain’s Mammals 2018: The Mammal Society’s Guide to their Population and Conservation Status.’
  
Diet: Seeds, green plants, fruits and animal foods. In a mixed deciduous woodland: acorns, ash and sycamore seeds for most of the winter, buds in early spring, caterpillars, worms and centipedes in early summer and blackberries and fungi in the autumn. Food is cached in underground burrows. Food remains are found in disused bird nests, on tree stumps and in sheltered feeding places between the roots of trees or under ledges. They tend to leave the flesh of fruit and eat only the pips.
 
General Ecology: Most wood mice live in underground burrows. The burrows are fairly complicated and may include nest chambers and food stores. Burrows probably survive from one generation to the next and will be enlarged or modified as required. Nests are commonly made of leaves, moss and grass. They are usually built below ground under the roots of shrubs or trees but occasionally are found in holes in trees, buildings and bird or dormouse nest boxes. Additional nesting material is used in autumn and winter; often the mouse blocks the entrance to the burrow with leaves, twigs or stones.

Individuals will nest communally in the winter but in the spring females usually take up their own home ranges and nest singly. However, home ranges shared by two females have been observed. Breeding males range over larger areas occupied by a number of females.

Their predators include foxes, weasels, owls and domestic cats. Wood mice are important prey for tawny owls; when numbers of woodland rodents are low, owls may fail to breed.

Breeding: Litters of 4-7 young are born in successive pregnancies from March to October but autumn litters are small. The babies are born blind (eyes closed) and hairless. They are weaned at 18-22 days of age when their weight is about 6-8 grams. Growth in the summer is rapid and females can become pregnant when they have reached a weight of 12 grams. Breeding may continue over the winter if a good food supply, such as a heavy acorn crop, is available.
 
Conservation Status: Wood mice have no legal protection and conservation does not seem necessary as recolonisation after mortality is often rapid. Wood mice can be beneficial to man by preying on harmful insects, and many trees and shrubs germinate from forgotten wood mouse food stores.

Studies of woodland seed crops and population numbers organised by the Mammal Society show that the seed crop size strongly influences wood mouse numbers in the same autumn and in the following summer (more food leads to higher numbers and better survival). Numbers are probably synchronised: highs and lows tend to coincide in different parts of Britain, possible because tree seed crops are synchronised.

Identification

Sandy brown fur with white/grey underside and a long tail. Protruding eyes and large ears. Tail dark and hairy. Does not have yellow V-shaped collar across the neck which distinguishes the yellow-necked mouse, however, may have a smaller neck tie of yellow that does not reach all the way around. Head and body length 8-11cm, tail length 7-11cm.

 

Confusion species

House mouse (Mus domesticus)
Grey/brown fur all over, usually no contrast between top and underside, as opposed to wood mouse which has a clear contrast of red/brown fur on top and a paler (often white) underside. Smaller size than wood mouse and proportionately smaller ears (about half the size). House mouse has stronger smell and can leave greasy marks from its fur.

Yellow-necked mouse (Apodemus flavicollis)
Slightly larger than the wood mouse, with proportionately slightly larger eyes and ears. Paler grey underside than wood mouse. Usually more lively and loud than wood mouse when caught. If you get a closer look: unbroken yellow band around neck, joining forelegs, whereas in wood mouse there is just a longitudinal yellow/orange streak down the chest (this is the distinguishing feature between the two species, do not attempt to identify these two species without a close up view of this, they are usually too similar to tell apart without seeing this).

Harvest mouse (Micromys minutus)
Much smaller than wood mouse. Golden-brown on top with pale grey/white underside, whilst wood mouse has a red/brown coat on top with a contrasting pale (often white) underside. Small eyes and subtle ears (often covered by fur) whilst wood mouse has large eyes and ears.

Hazel dormouse (Muscardinus avellanarius)
Orange/yellow coat on top with yellow underside and white on throat, much paler than the wood mouse which has a red/brown coat on top with contrasting pale (often white) underside. Hazel dormouse has larger black eyes but wood mouse has larger, more prominent ears. Dormouse has a very furry tail which wood mouse does not have.

Voles
Voles are different to mice in that they have a more rounded muzzle, whilst the muzzle of a mouse is pointed. Voles have smaller eyes and smaller, more subtle ears that are often covered by fur. Mice eyes and ears are large. Voles often have shorter tails. There are exceptions of course: water voles have long tails and it is often said that harvest mice have vole-like proportions as they have a more rounded muzzle and subtle ears and eyes.

Derek Crawley, Staffordshire Mammal Group, says:

“On seeing a small mammal at a distance, for example on a road, even the way it moves can help identification; wood mice bound, whereas voles scuttle.”

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