ROOK. 27 



with frequent calls, the flock trails across the sky in loose for- 

 mation. On reaching the destination, whether feeding ground 

 or roost, the birds frequently descend in rapid, oblique flight, 

 twisting and turning with wings half-closed ; this is termed 

 " shooting," and is also indulged in during nuptial display. 

 The harsh "caw," though easily recognised, is subject to 

 individual modulation ; in most flocks one or two birds have 

 high-pitched voices, which, however, are clearly distinct from 

 the sharper calls of Daws. Emphasis and inflection, especially 

 when at the rookery, suggest to our ears anger, pleasure, 

 affection and other qualities, but the alarm note, a long harsh 

 call, is seldom varied. 



Though more of a vegetarian than other crows, the Rook is 

 on the whole beneficial ; to some extent it destroys grain and 

 roots, but its services in checking pests, especially wireworms 

 and " leather-jackets," the larvae of crane flies, outweigh the 

 damage. Infected plants and roots are torn up, and the earthen 

 chambers in which the leather- jackets lie are dug out whole. 

 Worms, molluscs and small mammals are eaten, and flocks 

 frequently feed on tidal banks and the shore. 



The colony or rookery is established in a clump of trees 

 frequently close to a human habitation, and many nests may be 

 built in one tree ; nests on buildings are rare. Most of the 

 rookeries are deserted after the young have flown, the colonies 

 from a wide area joining forces and nightly occupying a common 

 roost. During winter the members of a colony frequently visit 

 the rookery, where with much conversation courtship display 

 is indulged in ; in February these visits, usually in the early 

 morning, become more frequent, and destruction or reconstruc- 

 tion of old nests begins, but serious building is seldom started 

 until March. In the nuptial display much bowing and tail- 

 fanning is indulged in. Old nests are frequently repaired and 

 added to until they become huge and unwieldy masses of sticks, 

 but frequently the old structures are deliberately destroyed. 



