Mammals in the British Isles

The genus Sorex contains two British species, the common shrew, S. araneus, and the pygmy shrew S. minutus, the latter being our smallest British mammal. The enamel of the tips of the teeth is red in both species, which are distinguished by size, relative length of tail which is longer in the pygmy shrew, and colour of the fur, darker in S. araneus but lighter in S. minutus. The common shrew is found throughout England, Scotland and Wales and on many of the islands, but is absent from Ireland, Orkney, Shetland, the outer Hebrides and Man. The pygmy shrew, although less abundant, is found throughout the whole of the British Isles except Shetland, the Scilly and Channel Islands. The common shrew is peculiar in showing chromosome polymorphism, that is, the number and form of the chromosomes differs in animals from different parts of the country.62 Both species are annuals: young born in one summer breed in the next and die in the following autumn, so the winter population consists entirely of immature animals, and none normally lives through a second winter.

The water shrew, N. fodiens, is the only British species of the genus Neomys, and is easily distinguished by its larger size and the black colour of the fur on the upper parts; it too has red-tipped teeth. Although it is aquatic and has fringes of stiff hairs on feet and tail that aid in swimming, it is nevertheless often found at considerable distances from water in woods and hedgerows in similar places to those inhabited by other shrews. It lives in burrows in the banks of clear streams and ponds; when it enters the water the fur traps air so that it appears silvery. The fur nevertheless soon becomes wet and is dried on landing by squeegeeing through the tight fitting burrow. Its food consists of invertebrates and even creatures as large as itself such as frogs and small fish. It is found throughout the mainland but is absent from Ireland, Isle of Man, and the western and northern islands of Scotland. The water shrew is unique among British mammals in being the only one with a poisonous bite, because the submaxillary salivary glands contain a venom that paralyses small prey.

The other two species of British shrew belong to the genus Crocidura, at once distinguished from the rest by their white teeth. Their ears are larger than in the others, and the tails bear a number of long scattered hairs. They are found only in the Scilly and Channel Islands, where they live in habitats similar to those of the common and pygmy shrews. The lesser white-toothed shrew, C. suaveolens, is found on most of the Scilly Islands, Jersey and Sark; it was probably unintentionally introduced into Scilly from the continent by man. The greater white-toothed shrew, C. russula, is found only on Alderney, Guernsey and Herm in the Channel Islands. The water and greater white-toothed shrews reach a life span of eighteen months or a little more, but the lesser white-toothed shrew is as short-lived as the common and pygmy shrews.

ORDER CHIROPTERA – BATS

All the British bats are comparatively small animals, and all are solely insectivorous, and nocturnal or crepuscular. They generally catch their food on the wing but some carry their larger prey to habitual perches to eat it. During darkness they find their prey by echolocation or ‘sonar’, emitting pulses of high frequency ultrasound which are reflected back from surrounding objects to give a mental image probably similar to that produced by sight in other animals. The horseshoe bats emit pulses through the nostrils, the other species through the open mouth. All species hibernate during the winter, and become torpid for four or five months, though not continuously, for hibernation is interrupted by short periods of activity. Bats are long-lived in comparison with other small mammals, reaching an age of four or five, and sometimes over twenty years.

Fig. 1. Side and front views of the head of a horseshoe bat to show the details of the nose-leaf.

Family Rhinolophidae

Two species of this family are members of the British fauna, the greater and lesser horseshoe bats, Rhinolophus ferrumequinum and R. hipposideros. They are characterised by the possession of ‘nose leaves’, thin fleshy outgrowths arising round the nostrils but overlapping the fur of the face with their free outer parts. Their structure is complex and better described by a drawing than by words; the part over the muzzle and round the nostrils is crescentic in shape, hence the English, Latin, and latinised Greek names of these bats.

The nose leaf is part of the special echolocation system. The greater horseshoe bat has a wingspan of 34 to 39 centimetres and is thus one of our larger bats. Its natural roosts are in caves, but it also uses mines and the cellars and roof spaces of buildings. In the British Isles it is found only in southwest England and south Wales. The lesser horseshoe bat is one of our smaller species, with a wingspan of only 22 to 25 centimetres. It roosts in similar places to those used by the larger species, and has a larger range, being found in southwest England, all of Wales and extending into Yorkshire, and far to the west in western Ireland.

Family Vespertilionidae

All the other British bats belong to this family – fifteen species in seven genera. They are mostly small to medium-sized bats but the serotine and noctule equal the greater horseshoe in wingspan, and one, the rare mouse-eared bat exceeds it by up to six centimetres.

Of the fifteen species, six are common throughout much of the British Isles, though only one, the pipistrelle, is found everywhere except in Shetland; they are the whiskered, Natterer’s, Daubenton’s, noctule, pipistrelle, and long-eared bats. Five species are rare, or occasional vagrants – Bechstein’s, the mouse-eared, parti-coloured, Nathusius’ pipistrelle, and the grey long-eared bats. The remaining four species are intermediate, having a limited distribution within the bounds of which they may not be scarce. They are Brandt’s, the serotine, Leisler’s and the barbastelle bats.

Six species of the genus Myotis are British. The whiskered bat, M. mystacinus, is a small dark grey bat that roosts in trees and buildings and often hibernates in caves. It is found throughout England, Wales and Ireland, but is less common in southern Scotland and absent from the north. Brandt’s bat, M. brandti, so closely resembles the whiskered bat that it has only recently been recognised as a separate species, differing slightly in details of the ear and teeth; it is known from many parts of England and Wales but its overall distribution has yet to be ascertained. Natterer’s bat, M. nattereri, is larger, with a wingspan of up to 30 cm, and the fur brown above and light or white below. It can be distinguished from all others by the fringe of stiff short hairs along the edge of the bare skin joining the legs and tail – the interfemoral part of the patagium or double layer of skin that makes a bat in effect an aerofoil. It roosts in trees, buildings and caves throughout the British Isles as far north as central Scotland. Bechstein’s bat, M. bechsteini, very similar to Natterer’s bat but having longer ears and lacking the fringe of hairs on the interfemoral patagium, is a rare woodland bat that has occasionally been found in southern England, mostly in Dorset. The mouse-eared bat, M. myotis, our largest species with wingspan up to 45 centimetres, was known only as a rare vagrant until 1956 when a small colony was found in a cave in Dorset; another was found in Sussex fifteen years later. Daubenton’s bat, M. daubentoni, is medium in size, dark brown above and pale grey below. The ear is comparatively short, and the feet large. It is often seen catching insects flying low over water, but is by no means confined to this way of feeding and frequently hunts in other places. It roosts in hollow trees and buildings, and often hibernates in caves. It is found throughout the British Isles except the northern parts of Scotland and the Hebrides.

Of the genus Vespertilio only the parti-coloured bat, V. murinus, has been found in the British Isles, as a very rare vagrant from the continent. It is a medium-sized bat; the dark brown hairs of the back have white or buff tips which give a grizzled or speckled appearance. Similarly, the genus Eptesicus has only one British species, the serotine bat, E. serotinus, which is, however, a regular though localised member of the fauna. It is a large species with a wingspan of up to 38 centimetres, and has dark brown fur, paler below. It is mainly a woodland species but often roosts in buildings; in England it is found only in the southern and eastern counties as far north as the Wash.

Two species of the genus Nyctalus, the noctule N. noctula, and Leisler’s bat N. leisleri, are widespread though not universal in the British Isles; both have comparatively narrow pointed wings. The large noctule with a wingspan of up to 39 centimetres has dark yellowish or reddish brown fur. It is a woodland bat, roosting in holes in trees, and often flies well before dark, hunting high above the trees. It occurs throughout England and Wales, rarely in southern Scotland and is absent from Ireland. The smaller but similar Leisler’s bat on the other hand is found throughout Ireland but has a more restricted distribution in central and southern England. It, too, is a woodland bat, differing from the noctule not only in its smaller size but also in the colour of the fur on the back, which is reddish brown at the surface but dark brown at the bases of the hairs.

The pipistrelle, Pipistrellus pipistrellus, a small bat with a wingspan not over 25 centimetres, is our commonest species, being found throughout the British Isles with the exception of Shetland. It varies greatly in colour, ranging from rufous through shades of brown to almost black. It roosts commonly in buildings, in which its colonies may number several hundred animals. The closely similar Nathusius’ pipistrelle, P. nathusii, is slightly larger, but is known only as a vagrant, a single specimen having been found in Dorset in 1959.

The barbastelle, Barbastellus barbastellus, the only British member of its genus, is a medium-sized bat with black fur, the lighter tips of the hairs giving a frosted appearance. The ears are short but wide and joined at their bases above the face, thus differing from all other British species except the long-eared bat. Barbastelles roost in hollow trees and buildings, and sometimes hibernate in caves. The species is rather thinly distributed over England and Wales as far north as Cheshire and Yorkshire, and is generally regarded as uncommon.

The long-eared bat, Plecotus auritus, is a small species recognised by its enormously long narrow ears which are nearly as long as the head-and-body. When asleep it tucks the ears under the wings leaving the tragus, the lobe representing the ear-cover, of each side sticking up like a pair of spikey horns. It roosts in trees and buildings and frequently hibernates in caves; when feeding it often hovers to pick insects off the leaves of trees. It is widely distributed throughout the British Isles except in northern Scotland and most of the Scotch islands. The very similar grey long-eared bat, P. austriacus, slightly larger, greyer, and with broader ears, has only recently been recognised as a separate species. It has been found in the south of Dorset, Hampshire and Sussex, but may prove to be more widely distributed after further study.

ORDER LAGOMORPHA

This order contains the rabbits and hares, easily distinguished from rodents by the presence of a second pair of small upper incisor teeth immediately behind the large first pair. There are three British species. Oryctolagus cuniculus, the rabbit, has long been an established member of the fauna although it is not indigenous. It was introduced by man a little before A.D. 1200 from its native Iberian peninsula and north Africa to be raised in confinement for fur and meat; it subsequently escaped, became feral and increased so that it is now found everywhere in the British Isles. The myxomatosis epidemic of the 1950s reduced the population drastically, but numbers have now recovered in many places.

We have two species of hare, the brown hare, Lepus capensis, and the mountain hare, L. timidus, both considerably larger than the rabbit, and with longer, black-tipped ears and longer legs. Linnaeus named the only hare found in Sweden in his time L. timidus, and a species from South Africa L. capensis, not knowing that the brown hare of Europe differs from the mountain hare, or that its range extends from South Africa to most of Europe and much of Asia – hence the peculiarity that our native brown hare takes its scientific name from the Cape of Good Hope. The brown hare, distinguished by the black upper side of the tail, is found throughout England and Wales, southern and north-eastern Scotland. It is not native to Ireland, but has been introduced into the north, and also into many of the Scotch islands. The mountain hare is smaller, has shorter ears, and the upper side of its tail is not black. After the autumn and winter moult the coat is wholly or partly white, and becomes brown again with the spring moult. The mountain hare is indigenous to the highlands of Scotland and all of Ireland. The Irish mountain hare is considered to be a distinct subspecies slightly larger than the Scotch, and assuming a white coat incompletely or not at all during winter. Mountain hares have been introduced into parts of southern Scotland and some of the islands, the Peak district and north Wales.

ORDER RODENTIA

The rodents comprise the rats, mice, squirrels, beavers, porcupines, and cavies. They are mostly small to medium-sized animals, the largest, the Capybara, a huge cavy of South America, reaching a weight of over a hundredweight; few others approach this size. There are about 1,500 species of rodents; Simpson131 remarks that they are ‘believed to be as abundant individually and in variety as all other mammals put together.’ Fortunately we have only fifteen species living in the British Isles, eight of them introduced; one introduced and one indigenous species are extinct. The incisor teeth of rodents, separated by a long gap from the cheek teeth, are single upper and lower pairs with chisel-like cutting edges and long roots from which growth is continuous so that the loss by wear at the cutting edge is perpetually made good.

Family Castoridae

The beaver, Castor fiber, was exterminated in the British Isles about AD 1200, but had been scarce long before. It was abundant in the Fens during prehistoric times.

Family Sciuridae

The red squirrel, Sciurus vulgaris, our only indigenous species, is typically an inhabitant of coniferous forests, especially those of our only indigenous pine, Pinus sylvestris, though not confined to them. The fur is reddish brown above, white below, the tail is long and bushy, and in winter tufts of long hair on the ears are conspicuous. The hairs of the tail and ear tufts wear and bleach during spring and summer, leaving the tail almost white and the ear tufts sparse. The numbers of red squirrels have varied widely during 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 dormouse and the hedgehog are the only indigenous British mammals that hibernate; the winter nest is usually made underground or among litter at ground level. The dormouse occurs sparsely throughout England and Wales, becoming scarcer in the north, and is absent from Scotland and Ireland. Another member of the family, the fat dormouse, Glis glis, was introduced at Tring in Hertfordshire in 1902, and has since persisted and spread over a small area of the Chiltern Hills. It closely resembles a small grey squirrel, but has dark rings round the eyes. It inhabits woods, orchards and gardens, and, like the common dormouse, it hibernates, often in the roofs of houses.