ROOK 293 



The really large winter roosts are not as a rule at full strength before 

 September or early in October, though varying numbers may roost at 

 these sites from the close of the breeding season. Indeed, the winter 

 roost is normally also the site of an existing large rookery, and when it 

 is not there is reason to believe that it is usually, if not always, the site 

 of a former colony, as is known to have been the case in various re- 

 corded instances. ^ These large roosts are often of many years' standing 

 and comprise thousands of birds drawn from a large area. They are 

 commonly shared with jackdaws (Corvus monedula), and collectively 

 they account for the bulk of the winter population of rooks, but in most 

 districts there are also smaller subsidiary roosts, and here and there the 

 members of a single rookery may roost there throughout the winter. The 

 feeding territories corresponding to individual roosts are generally fairly 

 constant in a broad way, but in the absence of any natural boundaries 

 like the sea or a range of hills have apparently no very clear-cut fron- 

 tiers as a rule, and there is considerable evidence that in some places 

 flocks from different roosts may mingle amicably on the same feeding 

 grounds. 



The dispersal from the roost at daybreak is rapid, and the flocks pro- 

 ceed in a direct and purposeful manner to their feeding grounds, though 

 often with a pause to visit their own rookery for a short time. The re- 

 turn journey, on the other hand, is usually of a markedly leisurely char- 

 acter. The birds begin to move in toward the roost from the more out- 

 lying areas at a comparatively early hour, and in Northumberland Philip- 

 son (1933) found that by about 1 o'clock the peripheral areas of the 

 feeding territory were usually deserted. In the less remote areas flocks 

 may be seen feeding in the fields considerably later, but there is a gradual 

 move toward the roost, often in two or more stages with an interval of 

 feeding between. Very commonly the adult birds assemble at their own 

 rookery before moving off, and as the flocks and parties converge to- 

 ward the roost they frequently combine into larger bodies. In the 

 neighborhood of the roost there are often regularly used collecting 

 grounds at which large numbers of birds gather and feed for a time be- 

 fore the final move, and in the fields immediately adjacent to the dormi- 

 tory the earlier arrivals resume their feeding in a restless way for a time 

 before retiring. As more and more birds stream in excitement rises, and 

 the observer is treated to astonishing displays of acrobatics in the air be- 

 fore the fresh arrivals settle. The fields are now black with birds and at 

 last about dusk the whole body rises as if at a word of command, and 

 with much cawing the procession to bed begins. Above the wood the 



1 It will be \inderstood that this applies to the BrltUh Isles and cAimot be the c««e 

 in Gouthem Europe, where the rook occute only as • migrant. 

 667497— 40— M 



