The Mammal Society

For Evidence Based Conservation

 

Species – Harvest Mouse

Harvest Mouse – Micromys minutus

Taxon: Rodentia

Harvest mouse © Roy Rimmer
Harvest Mouse Red List Classification:
GB: Near Threatened   
England: Least Concern 
Scotland: Critical
Wales: Vulnerable 
Global: Least Concern

General fact sheet (click to download)

National Harvest Mouse Survey

Harvest Mouse Appeal

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 & 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.
 
Harvest mouse distribution (in green), taken from ‘Britain’s Mammals 2018: The Mammal Society’s Guide to their Population and Conservation Status.’
 
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.
Harvest Mouse breeding nest © Stuart Moore

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.

Confusion species

Hazel Dormouse (Muscardinus avellanarius)

Much larger than harvest mouse. Orange/yellow coat on top with yellow underside and white on throat, unlike golden-brown colour of harvest mouse, which also has a very pale grey/white underside. Prominent, big black eyes, whereas harvest mouse has small eyes. Medium sized ears, more prominent than those of harvest mouse. Furry tail. Harvest mouse tail is much less furry.

Like harvest mice, dormice also build nests. The main difference between the dormouse’s woven nest is that grass is detached from the stem to weave. Dormice nests are 10-15cm, are often found in trees and are made of woven bark or leaves, making them harder and less easy to compress.

House Mouse (Mus domesticus)

Much larger than harvest mouse. Grey/brown fur, unlike golden-brown of harvest mouse. Much more prominent ears than small subtle ears of harvest mouse and bigger eyes. Greasy fur, strong smell.

Wood Mouse (Apodemus sylvaticus)

Much larger than harvest mouse. Red/brown on top, darker than golden-brown of harvest mouse. Large eyes and ears, compared to small eyes and small subtle ears of harvest mouse. If you get a closer look: black fur on top of tail that is not present in harvest mouse. Wood mouse has white underside with longitudinal yellow/orange streak between forelegs.

Yellow-necked Mouse (Apodemus flavicollis)

Much larger than harvest mouse. Red/brown on top, darker than golden-brown of harvest mouse. Large, prominent eyes and ears, compared to small eyes and small subtle ears of harvest mouse. If you get a closer look: black fur on top of tail, not present in harvest mouse. Yellow-necked mouse has an unbroken yellow band across neck, joining forelegs.