284 BULLETIN 191, UNITED STATES NATIONAL MUSEUM 



mainly on open ground, resorting to both pasture and arable land. 

 Moorlands, heaths, marshes, and unreclaimed land are not so much 

 favored, though rooks may be met with at times on all such types of 

 ground and in some districts not rarely. 



Rookeries being easily located and the nests large and easy to 

 count with only a small margin of error, the rook is an excellent 

 subject for census work, as a result of which the breeding population 

 of the species over large areas of Great Britain has been accurately 

 determined in rec.ent years. The average density in typical agricultural 

 country is found to be about 16 nests (or 32 breeding birds) to the 

 square mile, with a variation, in cases of areas over 100 square miles, 

 from 5 nests (North Wales) to 33.5 nests (Upper Thames Valley) a 

 square mile. 



Courtship. — ^A fair amount has been written about the sex behavior 

 of the rook. It has been especially studied by Edmund Selous (1927) 

 and G, K, Yeates (1934), and others have contributed miscellaneous 

 observations, but the subject would still repay further attention. The 

 ordinary courtship display is of a simple kind and may often be ob- 

 served in the opening months of the year. The male bird, either in a 

 tree or on the ground, droops his wings and bows several times to the 

 female with outstretched neck, accompanying the movement with cawing 

 and fanning out of the tail. The female may or may not be disposed 

 to respond to these advances, but, if she is, her reaction usually takes 

 the fonn of fluttering her wings with the body depressed in a crouching 

 position. She may even make a slight answering bow from time to 

 time, and sometimes a display takes place in which the two sexes be- 

 have similarly, both birds fanning their tails and bowing to one an- 

 other and at least on occasions both fluttering their wings. 



Wing-fluttering accompanied by elevation of the tail is the female's 

 normal expression of readiness for coition, and she may take the 

 initiative in soliciting without any preliminary advances by the male. 

 The elevation of the tail is the diagnostic action in this connection, for 

 the wing-fluttering should perhaps be regarded as primarily a food- 

 begging action. Ceremonial feeding and coition are, however, so closely 

 connected that it is doubtful how far actions related to one or the other 

 can be properly dissociated. The display commonly leads up to the 

 presentation of food by the male, and this is generally followed by 

 coition, which in the breeding season normally takes place only on the 

 nest. Sometimes, however (though the contrary has been stated), it 

 may occur on a branch or on the ground. Coition and ceremonial 

 feeding oc.cur well into the incubation period, but the associated dis- 

 play is then hurried or absent. Often the male "simply flies straight 



