THE ROOK AND JACKDAW 31 



he alighted with slow dignity, leaving the plover to make a meteoric 

 headlong dash along the furrows, ending with a sudden lift and a fairy- 

 like descent. There occurred also a general wild chase in which about 

 a dozen rooks, daws, and lapwings took part. In all this there was no 

 sign of animosity, no persistent bullying, no attempt to strike or to 

 buffet, as is for instance the case when, in spring time, the rook 

 ventures into the field where the plover has made or means to make 

 its nest. It was all mere frolic, and when it ceased the birds stood 

 about the ground as they were before, and as if nothing had occurred. 

 That birds, like mammals, indulge in play is well known, but such play 

 between members of different species, though no doubt more common 

 than we suspect, is rare enough to merit passing notice. 



Besides these playful encounters, there are, of course, lively 

 disputes arising out of contested claims to worms, beetles, and other 

 delicacies, usually terminated by the disappearance of the disputed 

 object down the throat of one or other of the claimants, there being, 

 of course, after this event, nothing tangible to strive for. 



What helps, perhaps, to give to the rook the ecclesiastical air 

 referred to is the white about his head, contrasting with the black of 

 his feathering. The white is caused by the bare skin round the base 

 of the bill, a feature which distinguishes the species from all its con- 

 geners. How this peculiarity is to be accounted for is a question that 

 has long interested ornithologists, and deservedly so, because it raises 

 in a concrete form the fundamental problem of the origin of a specific 

 variation. The first explanation which naturally suggested itself was 

 that the absence of feathering round the beak of the "bare-faced 

 crow " was due to its well-known habit of probing the soil in search of 

 worms. But the facts do not favour this view. Observation has not 

 so far conclusively proved that the rook is in the habit of digging its 

 beak into the soil up to its eyes (Fig. 2, p. 5). During drought or 

 hard frost it can hardly dig at all, and has to be content to turn over 

 clods and stones, or find other means of subsistence such as is pro- 

 vided by refuse heaps, by charitable dispensers of bread and crumbs 



