L. Harrison Matthews - 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. 62Both 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.