298 CORVIDyE. 



stant companions during the day adding their share to the 

 bahel. Then occasionally follows one of the strangest sights 

 that an observer can witness. Mounted to a very great 

 height the Books will suddenly let themselves drop headlong, 

 twisting as they fall, to within a few feet of the trees or of 

 the ground, when they recover themselves and glide onwards. 

 One after another, as though they had all gone mad, they 

 precipitate themselves in this wonderful way, some of them 

 wheeling round and rising again to perform the feat a second 

 time. The indulgence of this very curious habit is com- 

 monly held to portend wind, but the belief, like that in many 

 other supposed prognostications of the weather by birds, is 

 probably erroneous. The motive however which urges the 

 Eooks is wholly unknown, and all that can be reasonably 

 concluded is that they delight in this performance.* Most 

 usually they content themselves by soaring and circling 

 over the trees for a short time and then perching, but this 

 last is not accomplished quietly or quickly, and it is generally 

 dusk before all have found a place, while after nightfall, 

 especially when the moon is shining, belated foraging par- 

 ties come trooping in, and their arrival always produces a 

 certain amount of disturbance. 



Besides the Rooks which stop with us all the year, this 

 country certainly receives in autumn the visits of some 

 foreigners, and it is hardly to be doubted that a portion of 

 our natives emigrate at the same season, and join the large 

 bands that in winter repair to the south of Europe. The 

 number of those that leave us, which by the analogy of other 

 species we may infer are mainly birds of the year, is perhaps 

 not very large, for the general practice of shooting the 

 "branchers" as the young on quitting the nest are called 

 in May and June greatly reduces the surplus population, 

 the amount of which, equally with the supply of food, controls 



* Waterton explains it as being merely the shortest way of effecting a descent 

 from the great height the birds have reached, but this can hardly be so since 

 they constantly return at the same elevation while the performance is gone 

 through comparatively seldom, and the fact that some of the birds having just 

 executed the movement will take the trouble of again mounting aloft and 

 repeating it testifies to its voluntary nature. 



