476 THE GROUSE IN HEALTH AND IN DISEASE 



habits referred to in other parts of this Report. The reason is usually 

 Grouse not pretty obvious, for it is found that in the districts where the Grouse 

 <mfome ry ^ no * wan der in the winter it is because there are no other moors 



moors. 



vicinity where the conditions will be more favourable 

 than on their own ground. On the west coast of Scotland, for example, 

 owing to the mildness of the climate, the Grouse are seldom driven off the 

 high ground by snow ; and on the moors of Yorkshire, though the general 

 elevation may be considerable, there are not the same marked extremes as 

 in the Scottish Highlands. This distinction is well shown by Mr Stuart-Wortley 

 in the Fur and Feather Series, where he gives two sketches to illustrate 

 the difference of conditions in England and Scotland, and in his chapter on 

 Grouse driving he states : " On a Yorkshire moor you are driving on the tops 

 all the time. If there is a high point on the moor, rocky and precipitous, 

 it is in extent probably a mere fraction compared with the acreage of good 

 moorland around it. On a Scotch moor you have usually a large acreage 

 above the line of your highest driving ground." 1 It follows that in Scotland 

 the Grouse is forced to leave the high ground in time of snow to seek his 

 food at a lower elevation, and the same motive will cause him to return 

 again in the spring to the fresh young heather on the "tops," whereas in 

 Yorkshire, where the climatic conditions are much the same on every moor, 

 he would gain little by such migration. 



Whether migration actually results in a crossing of blood has been often 



debated. Some naturalists contend that the migrating packs do not inter- 



breed to any extent with the birds upon the moor where they have 



Does mi- 



gration sojourned for the winter, but that they return to their own ground 



result 111 



crossing of with their ranks unbroken. The evidence available does not altogether 



blood ? 



support this view, and indeed it is doubtful whether it is always 

 the same birds which departed in the winter that reappear again in the 

 spring. It is difficult to obtain conclusive proof on the subject, but one or 

 two facts are suggestive. In the first place, it often happens that on ground 

 where there has been a light stock in the autumn, there is sometimes found 

 to be a heavy stock in the following spring, thus pointing to immigration. This 

 circumstance is usually associated with a moor on which the feeding is good. 

 Conversely a heavy stock may migrate wholesale in the autumn, and only 

 a few birds may return in the spring. The reduction of their numbers may, 



1 Fur and Feather Series, "The Grouse," pp. 152-153.- 



