50 THE ALPS IN JUNE. 



prove a very fertile source of ornitliological knowledge when 

 thoroughly understood. As I said before, the agents which 

 chiefly cause birds to move from one place to another (so far 

 as we know), are food-supply and temperature. Now we have 

 only to look at a raised map of Switzerland to see at once 

 how subject the birds must be to such incitements towards 

 change of place. Anyone who has been to Switzerland wiU 

 have noticed that the scenery falls into three great divisions— 

 that of the lakes and valleys, that of the Alpine pastures and 

 forests, and lastly, that of the regions on the border-line of 

 perpetual snow, running upwards to the higher snow-fields. 

 .The professional mountaineer pays little attention to any but the 

 last of these ; the botanist and ornithologist have, fortunately, 

 much reason to pause and reap a harvest in the lower levels, 

 which are incomparably more beautiful. For convenience sake 

 I will call the lowest, No. i ; the second — that of the Alpine 

 pastures, No. 2 ; and the highest. No. 3. The distribution of 

 birds in these three regions is continually changing. No. 3, 

 in the winter, is entirely devoid of life and food. The Eagles 

 and the great bearded Vultures, now very rare, can find not 

 even a marmot to prey upon, for they are all asleep in their 

 burrows. The Snow-finches and the Ptarmigan, which in the 

 summer delight in the cool air of an altitude of 8000 to 10,000 

 feet, have descended to No. 2, or even lower, compelled by want 

 of food and water : and so too the red-winged Eock-creeper, 

 the Water-pipit and others, which may be seen in summer 

 close to the great glaciers. In the same way the birds which 

 haunt No. 2 in the summer — I am speaking of those which 



