ROOK 291 



is of somewhat lower pitch than the more raucous croak of the carrion 

 crow, but actually the rook's voice has a much greater range of pitch 

 than the crow's. According to Nicholson and Koch (1936), who pre- 

 pared gramophone records of the voices of many British birds, the 

 rook's vocabulary has a range of about 425-1,800 cycles a second, while 

 the crow's range is only about 600-750. The ordinary caw is subject to 

 considerable modulations and variations, as anyone may observe who 

 listens to the sounds in a rookery in spring or at a roost in winter. 

 There are also other more or less distinct notes, and Edmund Selous 

 (1901) has recorded over 30 sounds, but his list is unsatisfactory, as it 

 includes too many sounds that seem to be little more than variants of the 

 same essential note. I have shortly mentioned some of the more distinct 

 notes in the Handbook of British Birds (1938), but a systematic and 

 critical study of the rook's vocabulary has yet to be made. On occasions 

 of exuberance in spring rooks are sometimes moved to a kind of un- 

 couth attempt at song. As I have noted in the work referred to, one 

 such performance is described as resembling a bass or guttural repro- 

 duction of the varied and spluttering song of the starling, and other 

 more or less discordant variations have been noted. 



Field marks. — The adult rook is easily told from other black-plumaged 

 Corvidae by its bare grayish-white face. But this characteristic is not 

 acquired until the first summer after hatching, and young birds with 

 fully feathered faces are not easily distinguished from carrion crows. 

 The bill of the rook is rather slenderer and the culmen usually less 

 curved, but this is not a very good character, as it is easy to find young 

 birds of the two species whose bills are so alike that they could not 

 possibly be distinguished by this feature in the field. A better character 

 is the loose baggy appearance of the feathering of the thighs, which is 

 noticeable at all ages. 



Enemies. — The rook has no enemies serious enough to constitute in 

 any way a menace to the species. The chief enemy is man, who destroys 

 a certain number because of depredations on his fields and at many of 

 the larger rookeries organizes regular rook shoots in spring, at which 

 considerable numbers of young birds recently out of the nest are de- 

 troyed. These find their graves in rook pies, which are generally 

 agreed to be excellent eating, though the writer has not tried them. 

 The peregrine falcon, and on the Continent the goshawk, will sometimes 

 take a rook, and the golden eagle has also been recorded as doing so, 

 but this can happen only rarely, for the haunts of eagle and rook do 

 not overlap to any great extent and the eagle is nowhere common. The 

 common buzzard (Buteo buteo) and European sparrow hawk (Accipiter 

 nisus) are recorded as taking young birds occasionally, and if the 



