Micromys minutus

Range & Status

Found through western and central Europe, through central Asia to Japan, and found patchily, south to China and Taiwan. Absent from most of Iberia and Scandinavia (Corbet & Harris, 1996; Harris & Yalden, 2008). In Britain, probably a post-glacial introduction, with a limited distribution; but it can occur in large numbers locally (Harris et al ., 1995). In England Harvest Mouse is found south and east of central Yorkshire, with scattered coastal populations in Wales and a few colonies in Scotland (Harris et al ., 1995). It is absent from Ireland. The Mammal Society is concerned about this species due to threats to its habitat (Mammal Society, 1996). Harris et al . (1995) estimate (an estimate of low reliability) a figure of 1,425,000 for England and Wales.

Regional Distribution

Historically Harvest Mouse was common in Cornwall. An indication of how common it was, at least locally, is given by a record of 142 killed, upon removal of a small rick of corn, on the Tregenver estate in 1866. In 1906 it was described as ' ... not uncommon about Penzance and has been taken at Hayle: about Truro and Falmouth it is local, but on the whole common. It has been captured on East Pentire, Newquay, at Bodmin, at St. Neot and at Launceston' (Turk, 1973). Present in 12 partial/full 10km x 10km squares during 1960-1973 (Turk, 1973), with an even distribution in Cornwall. In recent years there has been a big improvement in the number of records of Harvest Mouse for Cornwall, due to increased efforts to find them, although it is still very poorly recorded. It is probably present over most of Cornwall; however, there are gaps in the current distribution map, notably in the north-east. Harvest Mouse is absent from the Isles of Scilly.

Habitat & Ecology

Favours tall dense vegetation including meadow, wetlands, reed-beds, salt marshes, cereal crops (barley being least favoured), ditch sides, bramble patches, grassy hedgerows, recently planted farm woodlands and some legume and other crops. Selected habitats and species of monocotyledon used for nests are diverse. In seasonally flooded areas, large-scale movements take place from their breeding areas: this together with the winter die-back of tall grasses forces the use of different habitat at different times of year. In winter, field headlands, rough grass banks and the relatively new ' beetle banks' act as refuges. They also occasionally over-winter in Dutch barns (Corbet & Harris, 1996; Harris & Yalden, 2008). Our knowledge of their diet in the wild is poor (Harris et al ., 1995) with little improvement in this situation over a decade on: there is a lack of published data on animals living in natural surroundings (Harris & Yalden, 2008). Diet is thought to be insectivorous and granivorous.

Threats

Harvest Mouse is found in marginal and wetland habitats which are prone to being destroyed. During a survey in the 1970s, it was found that 12% of known sites were destroyed each year. Mean litter sizes have also declined for unknown reasons. Climate changes could have a significant impact of their numbers; it appears that they prefer a dry continental climate; heavy rain during the summer leading to high juvenile mortality, cold and wet terminating their breeding season. The increased use of pesticides could be a major factor in their decline (Harris et al ., 1995). Habitat changes such as the removal of field margins, hedgerows and wetlands have been implicated in their decline. Predation from domestic cats may be of local importance (Harris & Yalden, 2008). Present trends in nature conservation of reintroducing/introducing grazing schemes to marginal land, if not done with care, could provide a further threat in important areas which are free from the above problems (D. Lord, pers. obs. ).

Conservation

This species is classed as Lower Risk, Near Threatened by the International Union for the Conservation of Nature. The Harvest Mouse is not included in A Red Data Book for British Mammals (Morris, 1993), but is included in the Biodiversity Action Plan list for Cornwall.