Wildlife - the Harvest Mouse

PUBLISHED: 00:00 15 January 2016

harvest mouse

harvest mouse

Paul Hobson

Paul Hobson goes in search of the small but perfectly formed Harvest Mouse

harvest mouseharvest mouse

For a creature that is so ingrained into our wildlife folklore and conscience, it is amazing just how little we know about harvest mice – both in Derbyshire and in Britain as a whole. In past decades when farming seemed to be a gentler more wildlife-friendly practice and far more people worked the land, we became very familiar with the harvest mouse. As with most small rodents mice have the ability to breed rapidly and their population explodes if their food supply is abundant. It’s not hard to imagine fields of ripe barley laced with plenty of tasty weeds and insects as a harvest mouse nirvana. As summer progressed they got on with what they do best and by harvest time the fields of ripe cereals could be rustling with thousands of mini golden mice. I have read of grain ricks that actually vibrated as you lay back against them because of the huge number of mice they contained. It is clear why it got its name.

As our old system of agriculture met the modern world with its population increase and mechanical and chemical technological revolution, our fields changed dramatically. True, the yields were far greater and food was cheaper but the price we had to pay was a severe reduction in farmland wildlife. The recent State of Nature report (2013) makes for very dismal reading with banner headlines of 60 per cent of all species studied (3,148) declining with 31 per cent of those strongly declining. The two main causes seem to be habitat loss and degradation plus global warming.

The cereal fields of modern Britain are no place for our smallest rodent and in consequence it has deserted them almost totally. Harvest mice distribution is not well understood because they are difficult to watch. When I am doing my wildlife talks during the winter I am often told that people have harvest mice in their gardens or have seen them when out and about on a walk. I always ask them to describe what they have seen. I then explain the difference between a harvest mouse and a bank vole or a wood mouse. When I ask again if they think it was a harvest mouse they saw, probably in only one case in ten have they seen the golden mouse – the rest were voles or wood mice. The main factor that fooled them was that the mouse they had seen was climbing in vegetation or brambles. Both wood mice and bank voles are great climbers but both are much larger and darker. The bank vole is dark brown to russet with a short tail while the wood mouse is greyer with long back legs and a long tail. A harvest mouse is a small mouse, warm golden in colour (though young harvest mice and ones in poor light can be a bit greyish), with a long tail that it curls round the vegetation as an anchor.

Derbyshire’s harvest mouse distribution is becoming much better understood since the 1980s. Prior to this it was first mentioned that it occurred in the county by Glover (1829) who described its beautiful ball-like nest. Later, in 1905, Jourdain (one of Derbyshire’s greatest naturalists) mentioned that it probably occurred. Up to the 1970s little was understood about its distribution apart from the fact that it was more likely to be found in the lowlands than the North or West.

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From the 1980s onwards the main way to survey the harvest mouse has been to look for their nests in the winter when the vegetation is much shorter. We now know that they are more widely ranging than first thought and that they are dominantly found in reed canary grass wetlands and areas of rough grassland. There is a strong population around Carsington reservoir and they are found in many wetland areas. Places where you might not expect to find them but records show that they are present, are Bakewell, Chatsworth and Calver. They are probably far more numerous in the east and south of the county but many of the populations are small and fragmented. Fragmented populations are always vulnerable. One disease or a cold winter could wipe out the whole population, and as Britain’s smallest rodent it is susceptible to winter frosts.

The key to getting them better distributed is to create lines of connectivity – in the past we called these green corridors. They are in a sense the highways that wildlife uses to move around the countryside. Imagine a small colony of mice in a wetland at the end of a marshy field of cropped grassland. How do these mice get to the next wetland which is perhaps a mile or two away? Crossing the grassland is a rapid invitation to kestrels and barn owls to snaffle up the brave explorers. The way to help them is to plant headlands along each field margin, a strip up to 6m wide of rough grass and wild flowers. The mice then have a corridor that offers shelter, cover and food. They will readily adopt it and be able to reach new suitable areas.

The future for the harvest mouse is probably a good one. Although the numbers tumbled as we switched our agricultural practices, with sensible wildlife planning there’s a good chance that in the future you will come across this most gorgeous and very cute mini golden rodent when out on a ramble.

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