THE WOODMOUSE Apodemus sylvaticus

 

Recognition:

Dark brown fur with white/grey underside, protruding eyes, large ears, long tail.
Head/body length: 81-103mm; tail 71-95mm.
Weight: 13-27g.

General Ecology:

Found throughout Britain, the wood mouse is our most common 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. They are rarely recorded on higher exposed ground with little cover. Wood mice are essentially nocturnal but some individuals may venture out in daylight.

Wood mice eat seeds, green plants, fruits and animal foods. In a mixed deciduous woodland they eat acorns 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.

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 and 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. 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. Few adults survive from one summer to the next. Their predators include foxes, weasels, owls and domestic cats. Wood mice are important prey items for tawny owls and when numbers of woodland rodents are low owl breeding may not take place. Conservation:

Wood mice can become pests of stored food in buildings and will take bulbs, beans, peas and tomatoes from the garden. Generally they seldom cause economic damage. Minor losses to forestry and agriculture due to wood mouse feeding can be ignored when balanced against the consumption of weed seeds and invertebrate pests. They will, however, take newly sown sugar beet seed, sometimes causing the field to be redrilled by the farmer. This can often be avoided by later sowing in spring, when densities of mice are lower and germination of the seed is quicker. They are killed by rodenticides put down for rats or house mice and may die after eating slug pellets spread on cereal fields. 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.

Conservation:

Wood mice are extremely common and are found in almost all habitats. They are an important source of food to many carnivores and birds of prey. They have no legal protection.

Frequent Questions:

I have wood mice indoors and would like to get rid of them but not kill them. What can I do?
You can catch them in a "live Trap", which can be purchased from most pet shops, and then release them at least 2 miles away.

Wood mice are pests in my garden. How can I stop them?
Damage caused by wood mice to crops is sporadic, usually when their natural food is scarce. Food shortages are often enhanced by the use of insecticides. The best way to prevent this problem is to provide an alternative food supply. Cereals put out in small boxes is usually sufficient to divert the mice during the critical period after sowing.

What is the difference between wood mice and yellow-necked mice?
The two mice are easily confused, but the yellow-necked mouse is larger, about one and a half times the weight of a wood mouse. It has a bright yellow chest spot joining the dark upper fur on either side of the neck.

How can I study wood mice?
Details are given in the booklet Live: Trapping Small Mammals: A Practical Guide and in Mice and Voles.

Further Information:

 

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