Wood mouse

Apodemus sylvaticus

Order: Rodentia

Description: Dark brown/orange fur above, with grey-white on underside; may have a yellowish patch in the middle of the chest, distinguishable from the full ‘V’ chest band and whiter underside of the slightly larger and less orange yellow-necked mouse;  pointed muzzle; prominent ears; large black eyes; long scaly tail with fine hairs.

Size: Head and body length 8-11 cm;tail length is as long as the head and body; sexual dimorphism not evident.

Weight: 16-18 g (winter), 25-27 g (summer).

Lifespan: Up to 20 months, but many adults do not survive longer than 1 year in the wild.

Breeding: Breeding season March-November, with a peak in July-August. Females may produce up to 6 litters per year with 4-8 young per litter. Young are weened before 3 weeks and are sexually mature at 2 months. Both sexes are promiscuous.

Habitat: Found in woodland but alsomost habitats, including urban areas. Nests of leaves and shredded grass are usually found in a multi-chambered underground burrow system. They may also live in stone walls. Often enters buildings such as garden sheds. Wood mice may occupy bird, bat or dormouse boxes. The larger yellow-necked mousefavours well-established, mature deciduous woodland and is not as common as the wood mouse in Shropshire.

Diet: Seeds, nuts, grain, fungi, fruit. Invertebrates such as insects, worms and snails are also consumed.

General Ecology: Active year-round, primarily nocturnal and crepuscular, except in summer when occasionally active above ground during the day; stores food in the autumn; less likely to be active in rainy or cold conditions, or during a bright moon. Individuals may share burrows in winter, but are more territorial during the breeding season. Wood mice are agile climbers.

Video still of individuals that share a burrow climbing-see below

Climbing ability of wood mouse, also shows large reflective eyes – Jen Lloyd-Pain
wood mouse 2km2 to 2018

Distribution and main sites:  widespread and common but seriously under-recorded in Shropshire

Local Survey history: frequently caught in live traps on small mammal surveys.

Conservation Status: Wood mice are very common and widespread throughout Great Britain and Ireland; population of approximately 38,000,000 (Wembridge, 2012).

Threats: Predators include foxes, weasels, domestic cats and owls. Wood mice are important prey for tawny owls. Tanwny owls might not breed if wood mouse numbers are too low.

Action: no current concern about the wood mouse population.

Main recording methods: Small mammal traps (e.g. Longworth or BioEcoSS tube), footprint tunnels, owl pellets, camera trap, direct sightings.

A trail camera is useful for determining behaviours, but challenging to separate wood from yellow-necked mouse unless chest markings are visible. Even if distinguishing characteristics such as head shape and tail length are not easily identifiable, the eyeshine of large Apodemus sp. eyes is very bright (like headlamps!), and can be differentiated from voles as Apodemus sp. hop and jump in addition to running.

Note: a licence is required to collect owl pellets from nest sites.

Did you know? Wood mice have been discovered to make ‘signposts’ out of leaves, twigs or shells to help them navigate. This species is also known as the long-tailed field mouse.

Other Field Signs

Food remains: Nut shells and seed coats may be found at the base of a tree, among roots, on stumps, under logs and in corners of outbuildings.  Wood mice and bank voles open hazelnuts by making a round hole and leaving tooth marks around the rim. Only wood mice leave marks outside the hole, made by holding the nut against a stationery surface while gnawing. Conifer cones may be stripped from the length of the cone with scales neatly removed, as opposed to grey squirrel that is likely to strip the cone bare.

[Drawing of small rodent food remains-see below]

Submitted separately as a jpeg

Credit: FSC/Mammal Society

Photo of hazelnuts chewed by wood mouse:


Tunnel entrances: Round burrow entrances < 4cm (about the size of a 50p coin) can be found on the ground, especially under tree roots.

Tracks: Similar to voles, but narrower – fore 4 digits, 10-16 mm/hind 5 digits, 22 mm.

Droppings:  < 1 cm, hard when dry and does not crumble (unlike bat), no or minimal smell. Larger than bank vole, but difficult to identify to species.

References quoted/paraphrased: Couzens et al. (2017) Britain’s Mammals: A field guide to the mammals of Britain and Ireland; FSC/Mammal Society (2016), A guide to British mammal tracks and signs; Muir & Morris (2013) How to find and identify mammals; Strachan (2002) Mammal Detective; The Wildlife Trusts; The Woodland Trust; Wembridge (2012) Urban Mammals: a concise guide.

Text – Jen Loyd-Pain.

© Shropshire Mammal Group 2020