Part 14

The versatility of the Brown Rat is such that it would be idle to attempt any description of its habits. Every one knows at least some part of the story, and the whole of it would require a book. It is the most powerful natural enemy that civilised man has had to contend with, for it attacks him in his own strongholds, spoiling and wasting his food stores and destroying his property in general. There was a time when it could be looked upon more as a commensal because of the valuable scavenging work it performed; but since man has learned that it is safer to attend to this work himself the Rat has become a mere parasitical nuisance. Sir J. Crichton-Browne has estimated the annual loss to this country through the depredations of Rats at £15,000,000 (pre-war figures, 1908).

The Rat is so thoroughly omnivorous that it would be equally absurd to attempt a list of its food: there is nothing that can be eaten that the Rat will not eat. Therefore, there is no possibility of starving him out. Rat-killing campaigns that do not cover every square yard of the country can only have the effect of temporarily mitigating the nuisance; for the Rats' fertility is so great and so rapid that the loss of nine-tenths of a generation is quickly made good. A continental statistician has worked out the theoretical progeny of a single pair of Rats after ten years as reaching the appalling figure of 48,319,698,843,030,344,720! Of course, there is no great value in such a calculation, for it proceeds upon the assumption that every individual lives to become a parent, whereas in fact the mortality in all creatures of such fecundity is enormous, and there are few if any more survivors this year than there were last year. In other words, the great fertility of a race only suffices to make up the wastage from enemy attacks. But the figures serve to show what might happen if the natural control by Weasels, Stoats, Hawks, and Owls were suspended for a short time. But Rats are disseminators of bubonic plague with the aid of their special species of flea.

*Water Vole* (Arvicola amphibius, Linn.).

In certain directions it appears that failure is the lot of those who have spent the greater part of their lives in trying to spread enlightened views as to the true nature of our native animals and plants. Among a number of such failures two or three may be briefly cited here: you cannot persuade a countryman that a slow-worm is not a snake, that all snakes are not poisonous and to be killed at sight, and that the comparatively inoffensive rodent now to be described is not a rat and of rat-like nature. The name of Water Rat is general as a true folk-name.

The Voles are of heavier build than the Rats, the head is shorter, thicker, and the muzzle rounded instead of being pointed; the limbs are shorter and the hairy tail is not much more than half the length of the head and body. The eyes are small and short-sighted, and the small round ears scarcely project from the surrounding fur, though when listening intently the Vole erects them and makes them more conspicuous. Linnæus, following Ray, described the Water Vole as having webbed feet, but this is incorrect, though the toes of the hinder foot are connected at their base. They are naked and pale pink beneath, with five rounded pads, but above are clothed in stiff hairs. The thick, long, glossy fur is of a warm reddish-brown above, sprinkled with grey, and on the under parts yellowish-grey. This applies chiefly to the male; the female is slightly smaller than her mate, is less bright and more greyish-brown in her coloration. The average length of head and body is seven and a half inches, and of the tapering, ringed tail about four and a half inches. It sometimes occurs with black fur, especially in East Anglia and Scotland; and these examples are usually reported as the Black Rat. Some modern authorities recognise it as a sub-species (reta).

Although it has not the webbed feet that Ray attributed to it, its swimming and diving powers are of a high order. Often in walking near a stream or pond, the loud sudden "plop" as it drops into the water is our first intimation that the Vole is near. We may occasionally track his course under water, but as a rule he at once disappears into his burrow in the bank, sometimes by an under water entrance, and may regain the bank by an upper exit. These burrows, in which the Vole spends most of the daytime, often occasion considerable damage, as to the dykes in the Fenland, and where ponds have been constructed by artificial banking. Otherwise, the Water Vole must be pronounced an entirely inoffensive rodent, in spite of the libels that accuse him of capturing waterfowl and fish for which he is unfitted. He has been seen grubbing among the mud at the bottom for caddisworms and other insects, freshwater snails and the like; otherwise his food appears to be restricted mainly to the stems of horsetails and the succulent grasses, flags, loosestrife, and sedges that grow along the banks. Mr. A. Patterson says that in East Anglia he eats dead fish and living swan-mussels--also crayfish; but prefers the stems of the succulent grasses that grow in shallow ditches. That he is not a strict vegetarian appears to be proved by the fact that he is sometimes captured in rat-traps that have been baited with meat. St. John says that in spring, before the grasses are much grown the Water Vole feeds largely upon toads, rejecting the feet which it bites off and leaves in little heaps. We have been assured by a Surrey woodlander of long experience and an intelligent observer, that he has known the Water Vole on several occasions to indulge in very young chickens; but he admits this is a very rare occurrence and that it scarcely detracts from the Water Vole's reputation as a vegetarian.

On the flanks, about halfway between the shoulder and the tail, will be found a pair of wrinkled glands which secrete a greasy matter with a musky odour. These are present in both sexes. Though the odour probably protects the Water Vole from some animals that might otherwise prey upon it, it does not appear to be objectionable to the Heron, the Owl, or the Stoat. When, to escape from real or fancied danger on land it suddenly dives into the water, it is not always to safety, for pike, large trout, and eels have been observed to seize them.

The Water Vole does not hibernate; but it has been said to lay up considerable stores for the inclement season when food will be scarce and difficult to find. These stores consist of nuts, beech-mast, acorns, and the creeping underground stems of the horsetails. During the milder nights that come in winter he issues from his chamber in the bank and feeds upon young willow shoots; and though mainly a nocturnal animal will often take advantage of the higher temperature at midday during the winter. It is often found in fields far away from any water.

The female constructs a thick-walled globular nest of reeds and grasses in the chamber under the bank, or in a hollow willow or a bird's nest, and there brings forth her litter of about five (two to seven) naked and blind young. The process is repeated three or four times during the season.

The Water Vole is generally distributed in Britain, but does not occur in Ireland, or the Scottish islands; nor is it known outside Britain.

The surface of the molar teeth in all the Voles presents a pattern of alternating triangular prisms. In the Water Vole and the Field Vole these teeth are not rooted in the jaw; in the Bank Vole they are in the adult.

In addition to the definitely black sub-species (reta) referred to above, the southern brown sub-species occasionally throws up black, pied, or albino variations.

*Field Vole* (Microtus agrestis, Linn.).

To country folk the Field Vole is known generally as the Short-tailed Field Mouse, to distinguish it from the Wood Mouse which is also the Long-tailed Field Mouse. Being different in organisation from the true Mice the attempt was made in natural history works many years ago to substitute the name Vole for these blunt-muzzled Rodents. Recently, after about a hundred years' use of the word Vole in all the works on mammals, Mr. Barrett-Hamilton has objected to it, at least in connection with the present species, on the ground that Field Vole is a duplication, the word Vole meaning "field." This would be almost as bad as Mr. Barrett-Hamilton's own use of such scientific names as Pipistrellus pipistrellus, Barbastella barbastella, Martes martes, and Capreolus capraea, which are duplications in the same language! In East Anglia this species is the Marsh Mouse, and in Surrey Dog Mouse.

The general appearance of the Field Vole is so different from that of a Mouse that it should be obvious at a glance that they are not very closely related. The general stumpy form with the blunt oval outline of the head, the short, round ears just protruding from the reddish-brown fur, and the short, rather stiff tail, are points sufficient to distinguish it from either of our Mice. The colour mentioned refers to the upper parts; on the underside the fur is greyish-white. The hind feet have six pads on the under surface as compared with the five of the Water Vole. The length of head and body is about four inches, and of the tail only an inch and a quarter, that is, about a third of the body length.

The chief resorts of the Field Vole are meadows and damp pastures, but it will also be found in gardens, orchards, and plantations, doing enormous damage in every place, for its food is mainly of a vegetable character. It must, however, be placed to its credit that it catches and consumes large numbers of insects, among them the destructive Larch Sawfly (Nematus erichsonii). It has extensive underground stores where it lays up food for the winter; but it is a mistake to say, as it has been said repeatedly, that the underground burrows include its summer nest. These burrows connect with a network of above-ground runs through the grass and herbage, with occasional holes that enable the Vole to bolt underground. These runs are made without disturbing the grass blades, which cross above them and so enable the Vole to run or creep along them without being seen by the hawk that circles high overhead. He is not so successful in eluding the Owl, who hunts much nearer to the ground and with the Weasel keeps a salutary check upon its increase. Beside a rank tuft of grass along one of these runs the female makes her nest, roofed with a circular dome of grass blades divided longitudinally and plaited and felted. It very much resembles the ground-nest of the Humble-bee, but on a much larger scale. There is nothing to distinguish it from its surroundings, so that only an eye trained to find it would see it. It may be detected by the finer character (due to shredding) of the grass. The parent enters or emerges from any point under the edge of the dome, and in the case of our uncovering the nest will at once bolt, leaving her five youngsters at our mercy. This we have found to be a characteristic callousness on her part. We have frequently torn off the roof of such nests suddenly, but have only been able to catch sight of the rapidly moving mother and trace her for a short distance along a run, so unhesitating and rapid was her flight. Like all our Rodents with the exception of the Hares, the young are naked and blind at birth, and there may be five, six, or seven in a litter. Those shown in the photograph, though their eyes were not open, had beautiful coats of short fur. There are several litters in a season.

In those districts where the over-zealous efforts of the gamekeeper have resulted in the partial extermination of the Weasel and the Owls, the increase of the Field Vole is so enormous and so rapid that they have at times become a plague. Crops are cleared from the fields, young trees in plantations destroyed by thousands, and even newly sown cornfields rendered unproductive by every seed being eaten. In the New Forest and the Forest of Dean great loss has been sustained at various times by their severing the roots of young trees that crossed their runs, and by their gnawing the bark of the young trunks. The most effective of the plans adopted for lessening their numbers was by sinking pits a foot and a half deep, wider at the bottom than at the mouth, into which vast numbers fell and from which they could not escape. More recently the South of Scotland suffered from a plague of "mice" that ate up everything in the fields, inflicting such serious loss to agriculture that a Government Committee was appointed to inquire into it, and it was found that the chief culprit was the Field Vole. Fortunately, when things were at their worst, a vast number of Short-eared Owls appeared upon the scene and feasted royally until there was scarcely a Vole to be found. It was found that the enormous increase in the numbers of the Voles was directly due to the warfare waged by keepers on Weasels and Owls. Matters are better, perhaps, to-day; but there are still too many keepers who destroy as vermin the very agents that keep down the real vermin. We still need a few landowners of the temper of Charles Waterton, who threatened to strangle his keeper if the latter molested a certain pair of Owls.

It was also shown at the Vole Committee of 1893, referred to above, that the Rook destroys great numbers of Field Voles--not only adults that chance to cross the fields where the Rooks are digging cockchafer grubs, but that they systematically search for the nests and eat the young.

As in the case of the Wood Mouse, there are several local races of the Field Vole that have arisen in the islands of the Orkneys and Hebrides, which have been elevated into distinct species by some recent authors. Thus, there are recognised the Hebridean Vole, the Orkney Vole, the Sanday Vole, and the Westray Vole. Mr. Barrett-Hamilton regards the true agrestis of Linnæus as not occurring in this country, where it is represented by several sub-species. The Common Field Vole described above, he says, is a distinct species, the M. hirtus of Bellamy. This, which he describes as "a newer, smaller form," he says "has replaced an older, larger M. agrestis, the latter now confined chiefly to northern regions, and with isolated southern colonies on the mountains." Seeing, however, that most modern authorities agree in retaining the Linnean name, we have considered it advisable to do so also.

The form that Barrett-Hamilton recognises as M. agrestis and calls the Northern Grass Mouse, is, so far as Britain is concerned, represented only in Scotland and its western islands by five sub-species which he names as under:--

Macgillivray's Grass Mouse (M. agrestis macgillivraii), a rich buff coloured form with thin fur, restricted to Islay, where it is rare.

Hebridean Grass Mouse (M. agrestis exsul), common on several islands of the Hebrides. Distinguished from the Field Vole by its much larger size and duller brown colour.

Eigg Grass Mouse (M. agrestis mial) restricted to the island of Eigg. Differs from M. a. exsul in its shaggy coat of abundant long hairs.

Highland Grass Mouse (M. agrestis neglectus) found on the summits of the highest Scottish mountains. It is larger than the Field Vole, with thicker fur and darker, browner upper side. It differs from M. a. exsul in the simpler character of the first molar tooth.

Muck Grass Mouse (M. agrestis luch), of which only three specimens have been taken, all on the island of Muck. About the same size as the Field Vole, it has a buff underside.

*Orkney Vole* (Microtus orcadensis, Millais).

So far back as 1805 the Rev. George Barry, in his "History of the Orkney Islands," mentions a rodent that was known locally as the Vole Mouse, which he believed to be the same as the agrestis of Linnæus. He says it "is very often found in marshy grounds that are covered with moss and short heath, in which it makes roads or tracks of about three inches in breadth, and sometimes miles in length, much worn by continual treading, and warped into a thousand different directions."

Towards the end of last century Mr. J. G. Millais obtained specimens, and on a critical examination found that they differed from the known forms in several details of skull structure and in the folds and angles of the teeth, sufficient in his opinion to constitute a new species, which he called Microtus orcadensis. It is larger than the Field Vole, with a longer and slightly broader head.