the last 300 years, but reached a peak at the turn of the century since when they have declined again. It is now widespread in much of Scotland, Ireland, Wales and northern England, but extinct in most of southern and central England. The causes of the fluctuation in the size of the population are not known.
The grey squirrel, Sciurus carolinensis, was introduced from North America and irresponsibly released in various places in the last quarter of the nineteenth century and the first of the twentieth. It has spread widely, and is now found in most of England and Wales, central Scotland and central Ireland. It is larger than the red squirrel, and has proportionally larger ears without conspicuous tufts. The fur is grey with yellowish brown streaks on the sides and feet and, in the winter coat, on back and head. The grey squirrel lives in woods of broad-leaved trees as well as of conifers; some town people regard it as an attraction in public parks, but in the country it is so destructive to young trees, fruit, forestry, agriculture and horticulture that it is now illegal to import or to release grey squirrels or keep them in captivity. Legislation, however, came too late to rid us of this pest.
Family Cricetidae
There were five species of voles in the British Isles, one probably introduced, and another that was injudiciously introduced but successfully exterminated. The last was the musk rat, Ondatra zibethicus, which escaped from fur farms, to which it had been brought from its native America. It became established in several districts about 1930, but a great official effort of destruction eliminated it seven years later.
The British voles are small mouse-sized animals with one exception, the water vole, often called the water rat from its larger size. The voles are distinguished from the mice by the rounded or blunt rather than pointed profile of the snout, and the comparatively small ears partly concealed in the fur. The diagnostic character of the different species is given by the pattern of the cheek teeth. Our four species are classified into three genera.
The bank vole, Clethrionomys glareolus, is recognised by the chestnut red fur of the upper side. It lives mostly in woodland, scrub and hedgerows, under which it makes runways and burrows, but it also habitually climbs among the branches of shrubs and small trees – so much that the late Oliver Hook, the well-known naturalist, nicknamed it ‘Cleth the Climber’, though the wood and yellow-necked mice are at some times and in some places equally or even more arboreal111a. The bank vole is often a destructive pest in country gardens. It is found all over the mainland of Great Britain, and on many of the islands, but is not indigenous in Ireland where it has recently been introduced, perhaps by some zoological practical joker, and now occupies a large area in the south-west. Four sub-species are recognised, each confined to a separate island – Raasay, Mull, Skomer, and Jersey. All are larger than the mainland race, and that of Skomer is much brighter in colouration.
The field vole, Microtus agrestis, is of smaller size but has greyish brown fur, smaller ears, and a short tail. It lives mainly in rough grassland and less often among scrub and dense cover; it makes runways and builds its nests under the thick mat of grasses, the stems and leaves of which form the greater part of its food. It is found throughout the mainland of Great Britain and on many of the Hebrides, but not in Ireland, the Isle of Man, Orkney or Shetland.
The voles of Orkney and Guernsey are slightly larger and darker, and differ from the field vole by a detail in the pattern of the cheek teeth. They are a separate species, M. arvalis, common on the Continent whence they were probably accidentally introduced into the islands long ago.
Our largest vole, the water vole Arvicola terrestris, about the size of a rat, lives near rivers, ponds and canals, into the banks of which it burrows to make its nest. Although it feeds mainly upon the grass growing near the banks it readily dives into the water and swims well. Its colour is generally brown, but populations of black water voles are present in north Scotland and East Anglia. The water vole is found throughout the mainland of Great Britain but is rare in north-west Scotland, and is absent from most of the islands and from Ireland. The paradox of a water animal having the scientific name ‘terrestris’ is due to the habits of this vole on the Continent, where it is not confined to the neighbourhood of water.
Family Muridae
The mice and rats differ from the voles in having proportionally larger ears and eyes, more pointed snouts, and longer tails. The cheek teeth differ in having low crowns with cusps. We have three indigenous and one introduced species of mouse, and two introduced rats.
The wood mouse, Apodemus sylvaticus, brownish yellow above and nearly white below, often with a coloured spot on the chest, was formerly called the ‘Long-tailed Field mouse’. It lives wherever there is cover, especially in woodlands and hedgerows and consequently is found throughout the British Isles and off-lying islands into many of which it was probably accidentally introduced by man. A large number of subspecies has been described none of which are now held to be valid. Although primarily vegetarian the diet is very varied and includes many small invertebrates.
A. flavicollis, the yellow-necked mouse, closely resembles the wood mouse but is larger and has a yellow band across the chest joining the colour of the upper side. It is found in many parts of England south of the Humber, and in Wales, but is absent elsewhere. It lives in similar places to the wood mouse, but more frequently comes into houses in autumn and winter. It was not recognised as a member of the British fauna until 1894.
The harvest mouse, Micromys minutus, is the smallest British rodent. Gilbert White of Selborne, the first naturalist to note its presence in England, wrote in 1768152 that he found two of them just counterbalanced ‘one copper halfpenny, which is about the third of an ounce avoirdupois’ or six to the ounce – they must have been thin mice for the average weight is about 6.0 grams or just over four to the ounce. The fur of the upper parts of the harvest mouse is bright reddish yellow and of the underside white. The nose is rather blunt, the hairy ear rather small, and the tail is prehensile. Harvest mice live among tall ground plants such as long grass and rough herbage among the stems of which they climb to seek their food and where they make globular breeding nests in summer up to about two feet above ground; in winter they live among the litter below. They are found, sometimes in abundance, throughout most of England and much of Wales, but are absent from the greater part of Scotland and the whole of Ireland.
The house mouse, Mus domesticus*, has dull brownish grey fur, slightly lighter below, occasionally much lighter. Unlike the other mice it has an unpleasant smell resembling that of acetamide. It is found wherever there are human habitations throughout the British Isles, feeding upon and spoiling man’s stored foods. It also occurs in hedgerows and fields away from buildings. It was introduced from the continent, no doubt unintentionally, about 2,000 years ago. Both the British species of rat are introduced, the ship or black rat about 900, and the brown or common rat about 250 years ago.
The ship rat, Rattus rattus, is commonly black in colour, but also occurs as two other forms, brown with grey underside or brown with nearly white underside. It was once widespread but is now found, with few exceptions, solely in the neighbourhood of sea ports, where it lives only in buildings.
The common rat, Rattus norvegicus, is larger than the ship rat and has comparatively smaller eyes and ears; the fur is greyish brown, lighter beneath. It lives in buildings of all sorts but also inhabits rubbish tips and hedgerows far from them. In addition it commonly lives in the open on the coast, especially on the shores of estuaries and salt marshes. It is found throughout the British Isles and off-lying islands, having replaced the once abundant ship rat. Charles Waterton, the early nineteenth century naturalist of Wakefield, expressed150 his extreme Jacobin loyalty by calling the common rat the ‘Hanoverian rat’ because it was introduced soon after King George I’s accession in 1714 – a name that was sometimes used by other writers.
Family Gliridae
Our only native member of this family is the dormouse, Muscardinus avellanarius, distinguished by its orange-brown fur, long whiskers, and hairy, almost bushy tail. It lives in broad-leaved woodlands, coppices and overgrown hedgerows, building a globular nest of bark fibre, grass, and leaves several feet, sometimes yards, above ground among shrubs. Apart from the bats the