Species of the day: Wood Mouse

By James Duncan

Learning and Engagement Officer

Despite being one of the UK's most widespread mammals, the Wood Mouse (Apodemus sylvaticus) lives a secretive life. There's thought to be approximately two thirds the number of Wood Mice in Britain than there are humans - whilst it's largely overlooked by us, it certainly isn't by the variety of mammalian and avian predators that rely on it for food. It's an adaptable little rodent that thrives in a multitude of habitats, the general exceptions being wet terrain or high, exposed ground. With their vulnerability to predation they save the vast majority of their activity until the sun goes down, erring towards areas of thick cover to conceal their movements. Unfortunately for wood mice they live fast and die young, rarely surviving more than two years, though the majority won't see a second summer. In order to compensate for a high metabolic rate they feed opportunistically, an omnivorous diet of seeds, fruits, buds, berries, insects, worms, slugs and fungi helping to fuel their forays. They will also cache food to help them through the winter, typically in excavated burrows, though the remains of food may be found almost anywhere, even in abandoned bird nests. 

To assist the Wood Mouse in its day to day survival, it has a rather magnificent set of super senses. Their exceptional sense of smell helps them to precisely pinpoint food sources, even those buried underground. Considerable ears located on the side of the head give them an all-round ability to listen for both predators and scurrying prey. Sizeable eyes let in a lot of light, giving them excellent vision, especially at night. The Wood Mouse is also an effective gymnast, able to climb, leap and scurry over most obstacles at the slightest sign of danger. Studies over the years have even pointed to an ability to navigate within their environment by way-marking - the true Hansel and Gretel of the animal kingdom, though admittedly not with the use of breadcrumbs. This system of spatial awareness had previously only been documented in one other mammal - us. Even allowing for this skillset, it's ultimately their diminutive size that makes them so vulnerable. When one of their key predators (the Tawny Owl) attacks in ghostly silence, they may stand little chance. The success of predators like the Tawny owl is in fact intrinsically linked to fluctuating Wood Mouse populations. Should a Wood Mouse be grabbed by a predator, it may shed part of the skin of its tail though this won't re-grow should it escape. 

As with most rodents their population is subject to high levels of mortality, though they have a very simple strategy to allow for this. Breed, and breed prolifically. They will typically do this all the way through spring, summer and autumn, though if food is plentiful breeding may happen in winter. They're not a hibernating species, instead entering into state of prolonged inactivity known as 'torpor.' During spring females will often disperse from communal winter nests in order to occupy a single territory, where they'll give birth alone. On average they'll produce up to eight young, but there may be four to seven litters per year. Given that females reach sexual maturity at around two months, it doesn't take long for their numbers to expand. The Wood Mouse also has a very similar looking relation, the Yellow-necked Mouse (Apodemus flavicollis) with which it was only separated in 1834. Whilst extremely similar, they can, with a close-up view be separated by the full 'neck collar' of flavicollis. 

Wood Mouse © Alan Price