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Wood mouse (Apodemus sylvaticus)

Also known as the field mouse, the common field mouse and the long-tailed field mouse, the wood mouse is the UK’s most common and widespread wild rodent. It has sandy brown fur with an off-white underside, protruding eyes, large ears and a long, dark tail. Some individuals have a yellowish patch of fur between their front legs, though not as pronounced as the yellow V-shaped collar found in yellow-necked mice. Wood mice are larger than harvest mice and browner than house mice.

The species is predominantly found in woodland, hedgerows and fields, but is highly adaptable and can be found in most habitats, if not too wet, including heathland, moorland and urban gardens. Wooded areas are favoured in winter and wood mice are rarely recorded on higher exposed ground. The species mainly easts seeds, especially in winter, but also consumes buds, berries fruits, nuts, fungi, roots, snails, insects, moss and tree bark. When plentiful, food is stored in underground burrows.

Wood mice are mostly nocturnal and generally live in underground burrows, but can also be found in holes in trees, buildings and nest boxes. Nests are typically made of leaves, moss and grass. Individuals nest communally in winter but females generally take up their own range in spring and nest singly. Wood mice do not hibernate but may enter torpor during severe winter weather. Few adults survive from one summer to the next.

Wood mice are polygynous, with multiple matings occurring between February and October. Females have a gestation period of 25-26 days and can have up to six litters of 4-7 young a year. Pups are born blind and hairless, are weaned by about three weeks and are sexually mature within two months. Breeding may continue over the winter if food is abundant.

Wood mice are common and widespread, and have no legal protection in the UK. Threats to the species include agricultural pesticides and rodenticides and predation by foxes, weasels, owls, snakes, hawks, mustelids, kestrels, dogs and cats.

Yellow-necked mouse (Apodemus flavicollis)

Closely related to the wood mouse, yellow-necked mice are only found in mature and ancient woodland in southern and southeast England, parts of the Midlands, and southern and central Wales. They have brown fur with a white underside and an unbroken band of yellow fur around the neck area. They are slightly larger than the wood mouse, with proportionately larger ears and eyes, and a long tail.

Yellow-necks favour mature woodland sites, particularly those with large, nut-bearing trees such as oak and hazel, but may also be found in hedgerows, gardens, orchards and scrub. They feed primarily on tree seeds, but also consume fruits, buds, shoots and occasionally small invertebrates. Yellow-necked mice are nocturnal and are adept climbers, making full use of the woodland floor and canopy when foraging and moving about their range. The species often develops extensive burrow systems among tree roots, which may have several entrance holes and food storage chambers, but also nests in holes in tree trunks, hollow logs and nesting boxes. Yellow-necked mice do not hibernate, though individuals may group together for warmth in winter.

Yellow-necked mice have successive pregnancies between February and October, producing litters of 2-11 young. Pups are born naked and blind, and their yellow collar becomes visible as a grey patch after about a fortnight. Young are weaned by about 18 days and may start breeding in the same year if born early in the spring, though most become sexually mature the following year.

Yellow-necked mice have no legal protection in the UK and, though reasonably common in some areas, population trends are unknown. The main threat to the species is loss of ancient woodland habitat, although they are also predated by owls, foxes, weasels, stoats and cats.

Harvest mouse (Micromys minutus)

The harvest mouse is Britain’s smallest rodent and is the only British mammal with a prehensile tail, which it uses to grasp plant stems as it moves through vegetation. They have reddish-brown fur with a white underside, small eyes and small hairy ears, and are smaller than other mouse species and with a blunter nose. Their tail is the same length as their head and body.

Harvest mice can be found a wide range of habitats and favour areas of tall grass and vegetation, including field margins, hedgerows, ditches, road verges, brambles, reed beds and salt marshes. They eat mainly seeds, fruit, berries and grain, although they will also consume insects, moss, roots and fungi.

Harvest mice are mostly nocturnal, though they may be active during the day in warmer months. They are extremely active climbers and are the only British mammal to forage and build nests of living woven grass well above ground. Females build tennis-ball sized maternity nests on the stalk zone of grasses during the breeding season, while both males and females build golf-ball sized solitary nests that may be in use year-round. Harvest mice do not hibernate but are less active in winter, when they stay closer to the ground for warmth.

Harvest mice breed between May and October, and females can have two to three litters of three to eight pups a year. Young are born blind and hairless, are weaned by about two weeks and are sexually mature by four weeks.

The main threats to the species are habitat degradation and changed agricultural practices, particularly intensive field margin and hedgerow management, and pesticide use.

Harvest mice are also vulnerable to extreme weather events and to predation by owls, hawks, stoats, weasels, corvids, foxes and cats.

Harvest mice are a UK Biodiversity Action Plan (UK BAP) species, meaning conservation action is deemed necessary to reverse their decline. The species is classified as ‘Near Threatened’ on the Mammal Society’s IUCN-approved Red List of British Mammals. While present in Somerset, population trends are unknown.

House mouse (Mus domesticus)

Believed to be native to Asia, the house mouse is highly adaptable and has colonised most parts of the globe thanks to its close association with humans. Evidence suggests the species has been present in the British Isles since the Bronze Age.

House mice have grey/brown fur, large, rounded ears and a pointed muzzle with a long, brownish-pink, and hairless tail. The species generally lives in close proximity to humans, and is most common in houses and agricultural buildings. It may also be found in cultivated fields, hedgerows and woodland, but is rarely found far from human habitation. House mice are omnivorous but in the wild feed primarily on plant matter, supplementing their diet with insects and carrion where available.

Wild house mice can occur alone, in pairs, small family groups or larger groups comprised of multiple families. They are generally nocturnal, don’t hibernate and live in underground burrows, often comprised of complex networks of tunnels, nests and storage chambers. The species is polygamous, with females and males mating with multiple partners. Females sometimes form communal nursing groups, where young are fed indiscriminately.

In the wild, house mice have a breeding season of April to September. Females have an average of 5-10 litters of 5-8 pups a year. Young are born hairless and blind, are weaned by 23 days and reach sexual maturity at 5-7 weeks. House mice are commonly viewed as a pest and are frequently subject to poison and trapping. The species is frequently predated by domestic cats, weasels, rats and barn owls.

Common and widespread, the house mouse has no legal protection in the UK.

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