Harvest mouse

Compared to other British mice, the harvest mouse is tiny, and has a blunt nose, small eyes, and hairy ears. The tail is prehensile and the same length as the body. The fur is russet orange above and white below. It is mainly found south of central Yorkshire.

Taxonomy chart

Animalia - Chordata - Mammalia - Rodentia - Muridae - Micromys - Micromys minutus

Conservation status: UK Red List

GB: Near Threatened   

England: Least Concern 

Scotland: Critical

Wales: Vulnerable 

Global: Least Concern

Species information

Habitat:A wide range of complex habitats that have tall grasses and other vegetation, including tussocky grasslands, hedgerows, field margins, road verges, reed beds and ditches.

Description: Blunt nose, small eyes, and small hairy ears in contrast to other British species of mice and also much smaller; prehensile tail the same length as the head and body; russet orange fur with a white underside.

Size: 50-70mm.

Weight: 4-6g.

Lifespan: 18 months on average.

Origin and distribution

The harvest mouse is a native species. It is mainly found from central Yorkshire southwards. This species occurs in Scotland and Wales but increased survey effort is needed to improve our understanding of the species distributions in these countries as they may be seriously under recorded. Areas of tall grass provide favourable habitats, such as cereals, road side verges, hedgerows, reed beds, dykes and salt mashes where nests can be built.

Diet

They eat a mixture of seeds, berries and insects, although moss, roots and fungi may also be taken. Harvest mice sometimes take grain from cereal heads, leaving characteristic sickle-shaped remains. Noticeable damage to cereal crops is extremely rare.

General ecology

Harvest mice are extremely active climbers and feed in the stalk zone of long grasses and reeds, particularly around dusk and dawn. Their hearing is acute, and they will react sharply; they either freeze or drop into cover in response to rustling sounds up to 7m away. Harvest mice have high energy requirements; the cost of being warm-blooded and coping with a high surface-to-volume ratio.

Breeding nests are the most obvious sign indicating the presence of harvest mice. Harvest Mice are the only British mammal to build nests of living woven grass well above ground. Nests are around 10cm in diameter and tend to be found in dense vegetation such as grasses, rushes, cereals, grassy hedgerows, ditches and brambles. They are generally located on the stalk zone of grasses, at least 30cm above the ground in short grasses and up to a metre in tall reeds. Harvest mice also produce solitary or non-breeding nests, which are smaller, with a diameter of around 5cm.

Nests are built from leaves that have been split lengthways (strips roughly 1-2 mm wide) and are woven together to form the framework of the nest. These leaves are still attached to the plant, supporting the nest by keeping it attached to the surrounding vegetation (see below for some examples). In autumn, most nests will be brown in colour and the entrance hole can be visible indicating that the nest is vacant.

Harvest mice have many predators: weasels, stoats, foxes, cats, owls, hawks, crows, even pheasants.

Breeding

Harvest mice usually have two or three litters a year in the wild, between late May and October, but even into December if the weather is mild. Most litters are born in August. Cold wet weather is a major cause of mortality. There are usually around six young in a litter. The young are born blind and hairless but grow extremely quickly and start to explore outside the nest by the 11th day. The young are abandoned after about 16 days but continue using the nest which may by then start to look rather dilapidated. A fresh nest is built for each litter. Once all young have left a breeding nest, an entrance hole will become visible.

Conservation status

Harvest mice are listed as a BAP (Biodiversity Action Plan) Species because they are thought to have become much scarcer in recent years and they require conservation plans to reverse the decline. Changes in habitat management and agricultural methods are thought to be the main cause for the loss of populations from certain areas, although there have been no reliable studies to quantify this change.

Identification

Very small size weighing only 6g when adult. Fur is a sandy brown colour with a paler underside. Has a blunt muzzle, small eyes and small hairy ears. The prehensile (capable of grasping) tail is the same length as the head and body. Only 5-7cm long.

Download resources

General fact sheet

National Harvest Mouse Survey