110 THE CAPERCAILLIE. 



outlet towards the west, the wave of advance has been forced 

 up the valley until it has reached beyond the limit of spruce, 

 Scotch fir, and larch. The inevitable law exists that there is 

 a distinct limit to the population of a species in any one 

 locality, regulated by the size, capabilities, and amenities of 

 the area, and when this limit is reached and exceeded the 

 surplus population is forced to seek new ground. Further, as 

 the internal pressure continues and increases, the greater 

 difficulties will be faced and surmounted by the pioneers, in 

 order to fulfil the destiny of the species, and the amount of 

 success achieved will depend upon the hardihood and " fitness" 

 of the species in the struggle for existence. 



The easiest and most natural courses of advance follow 

 the valleys, up or down stream, or stretch along the wooded 

 foothills and slopes, preferring, as already pointed out, the 

 sunny exposures. This is clearly illustrated by the fact, that 

 Capercaillies in a comparatively short space of time reach and 

 populate more remote localities in the directions whence the 

 great valleys lead them, than they do in those directions 

 where mountainous or treeless country intervenes. 1 



The beau-ideal of a safe harbourage and permanent home 

 for the Capercaillie would then appear to be as follows : 

 A forest of spruce, Scotch fir, and larch, mixed, of, say 700 to 

 1000 acres or more in extent, having a southern exposure, or 

 lying well to the sun, of which forest certain portions say a 



1 The comparative rate of advance by valleys and over mountains is illus- 

 trated to choose amongst a great mass of similar statistics by the extreme 

 limit reached by the Tay valley route in 1877 (vide Map), and the distance 

 reached at Loch Kennord in the same year ; the former Milngavie near Glas- 

 gow some 45 miles in a direct line from Taymouth, and the latter only 7^. 

 Or, to select another example the limit reached by the Tay valley route to 

 Dunkeld, and thence by Strathmore into Forfar in 1865 (Brechin district 

 over 50 miles in a direct line from Taymouth), as compared with that reached 

 in Glenshee in the same year (Dalnaglar, only about half that distance in a 

 straight line from Taymouth). I am inclined to think, judging from a large 

 mass of data, that the birds rarely, or only under exceptionally strong pres- 

 sure, cross mountain tracts, unless they can vieiv forest-covered country beyond. 



