The Annals of Scottish Natural History
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RETURN TO LIBRARY OF MARINE BIOLOGICAL LABORATORY WOODS HOLE, MASS. LOANED BY AMERICAN MUSEUM OF NATURAL HISTORY The Annals OF Scottish Natural History A QUARTERLY MAGAZINE WITH WHICH IS INCORPORATED Naturalist EDITED BY ]. A. HARVIE-BROWN, F.R.S.E., F.Z.S. MEMBER OF THE BRITISH ORNITHOLOGISTS' UNION JAMES W. H. TRAIL, M.A., M.D., F.R.S., F.L.S. PROFESSOR OF BOTANY IN THE UNIVERSITY OF ABERDEEN AND WILLIAM EAGLE CLARKE, F.L.S., F.R.S.E. NATURAL HISTORY DEPARTMENT, ROYAL SCOTTISH MUSEUM, EDINBURGH 1905 EDINBURGH DAVID DOUGLAS, CASTLE STREET LONDON: R. H. PORTER, 7 PRINCES ST., CAVENDISH SQUARE The Annals of Scottish Natural History NO. 53] 1905 [JANUARY ON THE VOLE AND SHREW OF THE ORKNEY ISLANDS. By WM. EAGLE CLARKE. With Report by Prof. O. CHARNOCK BRADLEY, M.B., C.M. IT is a somewhat remarkable fact that since 1848, when Messrs. Baikie and Heddle published their excellent for " the date Historia Naturalis Orcadensis," until the past year, 1904, no naturalist seems to have paid any attention to either the Vole or the Shrew inhabiting the Orkney Islands. The consequence is that the misleading pardon- ably misleading, it should be said statements of these authors regarding the specific identity of these Orcadian mammals have been unfortunately accepted by and repeated in all the subsequent writings on the subject with which I am acquainted. " " As regards the Vole, in the Zoologist for July 1 904 (pp. 241-246), Mr. J. G. Millais astonished British naturalists by describing the Orcadian Vole as a species new to science under the name of Microtus orcadensis, and as peculiar to 1 the Archipelago. To that date the Vole inhabiting the 1 Mr. Millais has informed me, since the above was written, that he has obtained this Vole in certain parts of Shetland. 53 B 2 ANNALS OF SCOTTISH NATURAL HISTORY islands had been regarded as the Short-tailed Vole (Microtus agrestis], a species which is common and widely distributed over the mainland of Great Britain. It would not have been so surprising had this Vole proved to be a racial form of some European species, but that it should be entirely distinct from any of its con- geners is certainly a most remarkable fact. Indeed it is not too much to aver that this little mammal is, from a scientific standpoint, among the most interesting and im- portant of existing British Vertebrates. Microtus orcadensis, though undoubtedly quite a distinct species, shares certain peculiarities with both the Water Vole and the Field Vole. Thus, in stoutness of build, in the comparative prominence of the ears, in the density and colour of the fur (especially the tint of its under surface), and, broadly, in its cranial characters, it resembles the Water Vole. While in the shortness of its tail, and to some extent in its dental characters, it approaches the Field Vole. In size it is somewhat intermediate between these species, large specimens being nearly half as large again (40 per cent) as the latter, though it is decidedly smaller than the Water Vole. In colour it is sandy-brown above (the apical portion of the hairs being yellowish-brown, the basal slaty-gray) with black hairs below it is long protruding interspersed ; sandy rufous. Half-grown examples are duller in colour, being darker than the adults on both the upper and under surface, and in this respect they resemble the Water Vole of similar age. Mr. Millais' largest male measured 6.75 ins. (head and body 5.5, tail 1.25 ins.). The following are the comparative measurements and weights of the largest specimens ot Microtus orcadcnsis and M. agrestis in the collections of the Royal Scottish Museum : ON THE VOLE AND SHREW OF THE ORKNEY ISLANDS 3 ANNALS OF SCOTTISH NATURAL HISTORY my request. I am also deeply indebted to him for the drawings of the teeth. An examination of the skull of Microtus orcadensis (Millais), and a comparison of it with the skulls of other British species of Microtus and of Evotomys glareolus, the Bank Vole, disclose many features from which it may be contended that the Orkney Vole merits a place as a distinct species among the British mammalia. Measurements of the skull of this animal have been made according to a method 1 of craniometry suggested some short time ago. These measurements, and the indices computed from them, as well as similar measurements and indices of other species of Microtus and Evotomys, are given in the following table : ON THE VOLE AND SHREW OF THE ORKNEY ISLANDS ences mi^hto be met with in the examination of several skulls from the same species. Undoubtedly variations do occur among animals of the same species, but they are not so marked as those shown above. And, further, if there is variation in one or several points, there is agreement in most features. An analysis of the indices may be briefly summarised as follows : The breadth of the cranium (compared with the length) of M. orcadensis is approximately equal to that of M. amphibius, but markedly greater than that of M. agrestis and E. glareolus. The oblique height of the cranium is about the same in M. orcadensis, amphibins, and agrestis. In E. glareolus it is decidedly less. When the vertical height of the cranium of M. orcadensis is compared with that of the others, it is found to be not very different from that of E. glareolus, but less than in M. amphibius, and greater than in M. agrestis. A very striking feature in the skull of M. orcadensis is the degree of development of the temporal fossa, and, par- ticularly, the close approach it makes to the middle line in its more anterior part. This is shown by the Stephanie index, which is much smaller in this animal than in any of the others. Another very obvious feature in the cranium is the much greater sagittal diameter of the interparietal bone. This is very clearly demonstrated if the bone be measured in two directions transverse and sagittal and an index com- the transverse diameter taken as i oo. puted ; being 6 ANNALS OF SCOTTISH NATURAL HISTORY The face of M. orcadensis resembles that of M. agrestis in regard to its width. It is narrower than in E. glareolus, and broader than in M. ampJiibius. If the length of the cranium is compared with the length of the face, it is found to be slightly less in M. orcadensis than in M. ampJiibius, and decidedly less than in M. agrestis and E. glareolus. When the length of the face is compared with the length of the entire skull, M. orcadensis has a slight advantage over M. amphibius, and a decided advantage over M. agrestis and E. glareolus. Taking the two foregoing statements together, it is evident that the face is longer in M. orcadensis than in any of the others. The relative width of the palate is slightly greater in in but less than M. orcadensis than M. ampJiibius t distinctly in M. agrestis and E. glareolus. The molar teeth of M. orcadensis possess certain features to which attention must be directed. The number of in the first molar is and in the enamel-spaces upper 5 ; second, 4. In the third molar there are clearly 5 spaces, but the most posterior is partly divided into two. When this tooth is compared with the corresponding tooth of In M. agrestis there is found to be a striking similarity. it be M. agrestis there are 6 spaces. Therefore may claimed that in M. orcadensis there are also really 6 spaces, but the posterior two are not completely separated from each other. It is conceivable that, if other specimens were examined, separation might be discovered even greater than that shown in Fig. i, A 3. The spaces in the lower molar teeth are shown in outline in first molar has the three most Fig. 2, A. The 9 spaces ; anterior being incompletely separated, as is the case in second and third molar M. agrestis (cf. Fig. 2, B). The have 5 and 3 spaces respectively. Summarising, it may be said that the molars of M. orcadensis resemble those of M. agrestis except that there instead of are 4 spaces in the second upper molar 5. In considering all the features of the skull together, it is clear that, except in regard to the teeth, M. orcadensis is other more closely allied to M. amphibius than to any ON THE VOLE AND SHREW OF THE ORKNEY ISLANDS 7 British species. At the same time it departs sufficiently widely from Jlf. amphibius to justify the conclusion that it forms a distinct species. I. I, 2-. A. B A, B. FIG. i. FIG. 2. = A = Upper molars (right) of A Lower molars (left) of Jlf. orcadensis. J\I. orcadensis. = molars of B= Upper molars (right) of B Lower (left) M. agrestis. M. agrestis. As regards the Orkney Shrew. It has down to this date been considered an interesting fact, in the insular dis- tribution of British mammals, that while the Lesser Shrew (Sorex minutus] is the species found in the Hebrides and in Ireland, it was not only absent from the Orkneys, but was replaced there by the Common Shrew (Sorex araneus}. 1 make bold, however, to say that I very much doubt if the Common Shrew has ever been captured in the Orkneys. " " At the date of publication of Baikie and Reddle's Historia the Lesser Shrew had not been recognised as an inhabitant of our islands, so that it is not surprising that these authors should have regarded the Orcadian Shrew as being the same species as that which was common to Great Britain.