THE ORKNEY GRASS MOUSE 457 
the group became extinct through unsuccessful competition 
with JZ. agrestis neglectus, just as the latter succumbed in the 
southern and lowland districts before the advance of JZ. hirtus. 
The persistence of JZ. sarnzus in an island far to the south 
shows that these mice owe their survival to freedom from 
competition in islands rather than to any other factor; else- 
where they have probably succumbed to such competition, 
helped by the attacks of carnivora, from which large palatable 
mice inhabiting shallow burrows can only escape in the presence 
of moderately deep snow. 
THE ORKNEY GRASS MOUSE. 
MICROTUS ORCA DENSIS, Millais. 
1805. MUS AGRESTIS (species), George Barry, Wistory of the Orkney Islands, ed. i., 
314; ed. ii, 320, 1808 (part); Low, Fauna Orcadensts, 1813, 25 (part); T. E. 
Buckley, Trans. Nat. Hist. Soc., Glasgow, i., 49, 1883-86 (part). 
Local names and terminology :—Cuwttick or puttick (Millais) ; vole- 
mouse of Barry, 1805 (see under /7zstory), a name which seems to have 
been the source of the term “vole,” as already discussed above on 
pp. 398 and 443 (see also Edmonston’s Eztymological Glossary of the 
Shetland and Orkney Dialect, 1866). 
Distribution :—This mouse is confined to the Orkneys, where it is 
known from all the bigger islands except, perhaps, the rocky Hoy?; 
it is abundant in parts of South Ronaldshay, Pomona, Shapinshay, 
Rousay, Westray, and Sanday. 
History :—This mouse was first mentioned by Barry, minister of 
Shapinshay, in 1805 :—“ The Short-tailed Field Mouse (Wus agrestis, 
Lin. Syst.), which with us has the name of the vole mouse, is very often 
found in marshy grounds that are covered with moss and short heath, 
in which it makes roads or tracks of about 3 inches in breadth, and 
sometimes miles in length, much worn by continual treading, and 
warped into a thousand different directions” (in ed. ii., 1808; ed. i. not 
seen). 
Subsequently to Barry’s time the mouse appears to have been 
known to many naturalists, none of whom examined it critically. 
Baikie and Heddle appear to have confounded it with the Water 
Rat, other writers with J/. agrestis. In August 1886 Millais’s attention 
was attracted by some individuals which he observed in Pomona, but 
1 Note that Baikie and Heddle (Addendum, 97) record the capture of two 
specimens of Mus amphibius in the burn by Rackwick, in Hoy, by M. F. Heddle in 
September 1844. 
VOL. II. 25G 
