Surrey Wildlife Trust spotlight on the harvest mouse...

Harvest Mouse

Harvest Mouse - Credit: Archant

The harvest mouse is synonymous with the British countryside, but numbers are declining. Surrey Wildlife Trust’s Dave Williams reports

When we hear the name “harvest mouse” mentioned, most of us will probably conjure up a picture of a tiny mouse with its tail wrapped around a corn head in a field.

However, recent surveys suggest that they now prefer reed beds to cornfields. This is probably because the reed beds contain the tall strong stems that they need for nesting. Farming methods have also changed and the earlier harvesting is obviously bad for them, as they lose their habitat, but also more pesticides are used, which may be harmful or repellent to them.

The harvest mouse is one of Britain’s smallest mammals, weighing around six grams each, or about the same weight as a 20p piece. Their body is about 60 to 70mm long and their tail is about the same length. The tail is prehensile, which it uses to climb and search through the lightweight stems giving it an excellent sense of balance. Being so small and secretive, it makes them hard to spot and consequently harvest mice have often been described as one of the most under-recorded species in Surrey.

Very little is known about the status and distribution of this tiny and endearing creature, but it is thought to be declining. They occur throughout England and Wales, and as far north as Yorkshire but are also found in most of Europe and even as far east as Japan!

Harvest mice live in a variety of habitats and are sometimes found in roadside verges, motorway embankments, and many other locations. They always favour areas of tall vegetation or tall grasses, where they can build their tiny, tennis ball size nests in the summer.

The little spherical shaped nests, used for breeding from May to October, are made by shredding and weaving grass or other material into a tight ball that remains attached to the stalks. They then line the nests by pulling in leaves through the outer wall. Winter activity Harvest mice abandon the nests in the winter and use ground level runs and tunnels of other small mammals, or winter nests in the base of thick grassland and tussocks instead. They do not hibernate, but have a three-hour rotational pattern of sleeping and feeding, eating a third of their bodyweight (two grams) every day.

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They have many natural predators including owls, so by examining owl pellets, for harvest mouse bones, information can be gained on their presence in that area. They live on seeds, berries and insects, but they may also eat fungi, roots and mosses. Though they may leave some evidence of where they have fed, perhaps tiny sickle shaped slivers of seeds, or their droppings, these are so small they are very hard to spot. This is why sightings of their discarded summer nests is of such great importance. They can be found in many grass and reed species such as the common reed (Phragmitesaustralis), reed canary-grass (Phalarisarundinacea), cocksfoot grass (Dactylisglomerata), false oat grass (Arrhenatherumelatius), tufted hair grass (Deschampsiacespitosa) and soft rush (Juncus effuses).

It is very important to record the presence of a declining species such as the harvest mouse, so that action can be taken to prevent their natural habitat from being fragmented or destroyed.

If you find any nests or know of any harvest mouse populations, please get in touch with me, Dave Williams, at the Surrey Wildlife Trust, on 01483 795440, giving details of the site and anything else you know about them. This will enable us to build up a clearer picture of Surrey’s harvest mouse population and help us with our work of conserving them and their habitats.


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