The Harvest Mouse in Cheshire - 1999-2000 Survey

Introduction:

• Harvest Mice (Micromys minutus Pallas), are currently the subject of much debate in Cheshire. Chester Zoo is initiating a breeding programme with a view to re-enforcing populations in the county.
• Harvest mice weave nests in monocotyledonous herbs that are difficult to find as they are woven from living grass, but become more visible in early winter as the grasses die off (Harris & Trout 1991).
• Suitable areas of habitat include cereal fields, rough grassland, reedbed and fen, and the Harvest Mouse can be the most abundant small mammal in wetland (Perrow & Jowitt 1995).
• In Britain it is most common in the South and East, but its distribution in North West England is uncertain. The West Midlands and Lancashire yielded three and two records respectively during the Mammal Society survey of the 1970s, while Cheshire, sandwiched between these two regions, had 13 records.
• The Cheshire records were mostly from the fringes of metres (Harris 1979). Only one record for Cheshire was found during a re-survey of the 1970s sites, but five of the 13 original sites, including Rostherne Mere (a National Nature Reserve), went unsurveyed. A record of a nest in Cock's Foot grass ( Dactylis glomerata ) growing inside a tree guard in a young plantation was the only other recent record, (1997, Aston).
• To investigate this apparent paucity of records in the last 20 years, a survey of the land covered by the Cheshire Wildlife Trust (Cheshire, the Wirral, Stockport, Tameside and Trafford) was planned for 1999 and 2000.

Methods:

• Methods currently employed for surveying include nest searching and stalk-zone trapping (used here), hair tubes and baited tubes.
• Nest searching can be quantified in various ways; in this survey, suitable habitat was searched in 30-minute blocks, recording the number of nests found per search, and the species of grass in which the nest was woven.
• All historical sites with adequate map references were surveyed by nest searching; two of the most recent sites were also surveyed by stalk zone trapping.
• Additional sites were chosen for survey through consultation with Phase 1 habitat maps, advice from colleagues at the Trust, and requests from landowners and rangers.
• Trapping was carried out on a small number of sites, as there were a number of limiting factors, including the time of year, access, and the proximity of public byways. Longworth traps were placed on platforms constructed from hardboard, plastic tubing and bamboo canes. These were then placed in a grid of 20 x 3 at 10 metre intervals in areas of long grassland or reed. Trap sessions at each site lasted four days, making a total of 240 trap nights per site.

Results:

• Signs of harvest mice were found in 24 one-km squares in Cheshire. 53 nests were found at 25 sites out of 126 sites surveyed (19.8%).

Table 1
Monocotyledonous herbs utilized for nest building by Harvest Mice in this survey, compared with national results from Harris (1979):

Table 2
Habitats from which Harvest Mice or their nests were recorded, in this survey, compared with national results from Harris (1979):

• For ease of comparison, "Marsh" from Harris (1979) was taken as "Fen" here. There was no corresponding habitat for "Rank grassland" in that study.
• 53 (98.1%) of records were nests, while only one (1.9 %) mouse was trapped. While this seems a low yield for trapping, the other sites that were trapped yielded no records from either trapping or nest searching.
• In this study, all records came from land under 500 feet, and no Harvest Mice were found east of Holmes Chapel. In the 1970s survey of Britain, 90.3% of all records came from land under 500 feet (Harris 1979), as did all 100% from the Sheffield area between 1980 and 1996 (Whiteley 1996).

Discussion:
The Harvest Mouse is still present, though local in the county, despite the paucity in records over the last 20 years.
The most common habitat for the mice in the county is fen (with 57.4% of all records), which occurs around the fringes of meres, along the bank of rivers and canals (such as the river Weaver navigation), and in wet meadows. In contrast, Harris (1979) found 57.7% of nest records were from "dry habitats".
The meres support reedbeds that dry out into Phalaris- and Carex-dominated fen beds, all habitats that support Harvest Mice. The fact that dairy grazing puts dry grassland at a premium also supports the bias towards wetlands.
The Countryside Stewardship Scheme may benefit the species, by creating harvest mouse-friendly habitats such as field margins and hedgerows.
A warm dry summer in 1999 may have meant that there was a large population produced that year.
The increase in records may simply reflect increased surveying; as 126 sites were surveyed during this study, resulting in 25 records (19.8%), compared to one record from eight areas (12.5%) of suitable habitat surveyed during the 1997 re-survey (T. Newman pers comm). One negative record from 1997, at Pickmere, proved positive in 2000.

References:
Harris S. (1979) History, distribution, status and habitat requirements of the Harvest Mouse (Micromys minutus) in Britain. Mammal Review 9:159-171.
Harris S. & Trout R C. (1991) Harvest mouse Micromys minutus pp 233-239 In: The Handbook of British Mammals, Eds. G B Corbet & S Harris 3rd Edition. Blackwell Scientific Publications, Oxford.
Perrow M & Jowitt A (1995) What future for the Harvest Mouse? British Wildlife 6:356-365. · Whiteley D. (1996) Harvest Mice in the Sheffield Area 1980-1996. Sorby Record 32:37-41.

Acknowledgements:
Robert Carthy and The Cheshire Wildlife Trust wishes to acknowledge the financial support of English Nature. Thanks to P. Morris and D. W. Yalden for use of photographs.