22 
The red grouse ( Tvtrao scoticus ) frequents the upper plateaus 
of the Scotch, English, and Irish mountains; it is most abun- 
dant in Scotland, less so in England, and comparatively scarce 
in Ireland. It rarely descends to cultivation, and when it does 
and feeds on cereals, the change of food produces disease, a species 
of pneumonia. The proper food of the red grouse is the tender 
young shoots of the plants mentioned in the diagram, Calluna 
vulgaris and Erica cinerea. The red deer and red grouse have a 
much wider geographical distribution in the British Islands than 
the zone above, they are both found in the islands of the 
Hebrides; while the red deer is distributed throughout the 
Continent of Europe, the red grouse is entirely confined to the 
British Islands. Their presence in the outer islands is in 
remarkable contrast with the higher zone. The nearest ally to 
the red grouse is the willow grouse of Scandinavia, all inhabi- 
tants of treeless regions. 
The food, Calluna vulgaris and Erica cinerea, is very 
widely distributed in the British Islands and throughout the 
Continent of Europe. I have no satisfactory explanation to 
offer for the restricted geographical area of the red grouse. It 
is a bird strong of flight, and perfectly capable of crossing the 
Channel or even to Norway. Glaciation may be the solution of 
the question, but it is confronted with many anomalies and 
difficulties. The red grouse is abundant in the Western district 
of the Island of Lewis, where the glaciation was relatively late, 
and clearly marked on every exposed rock; also in Sutherland, 
two prolific habitats of the red grouse, thus very largely 
diminishing the value of the theory of glaciation for the 
restricted distribution of the upper zone, the white hare and 
ptarmigan. However applicable to the higher zone, it entirely 
fails in this to account for the distribution in the British Islands 
of the red deer and red grouse. 
The next zone is the brown hare (Lepus timidus) and the 
black grouse (Tetrao tetrix). The black grouse, usually known to 
sportsmen as black game, frequents the hills above the tree line 
and the upper part of the tree line, just bordering the limits of 
cultivation. It occupies a well defined zone of the grasses under 
the Calluna vulyaris and Erica cinerea, mainly feeding on the 
young shoots and seeds of Agrostis. It is a larger and more 
powerful bird than the red grouse but inferior for sport. The 
brown hare has a wider range than the black grouse. The same 
difference in range is observed between the white hare and the 
ptarmigan. The narrower vertical range of the birds, with their 
superior power of locomotion, I think, can be explained by the 
quadruped’s more omniverous vegetable food. 
The next zone, the rabbit (Lepus cuniculus) and the partridge 
(Perdrix cinerea), do not go so high as the upper part of the 
zone above, but they overlap in the lower part. The partridge 
