8 BIRD BEHAVIOUR 



able ; it never acquires the habit of holding down 

 its food with one foot, though this would be of 

 vital importance to it in enabling it to consume 

 large articles of food when perched on a small 

 bough, and thus escape risk of ground enemies. 

 Though largely a ground-feeder, it hops and does 

 not run, and does not hold up its tail to keep it 

 clear of wet ; when courting it has a definite 

 display, with wings lowered and head and tail 

 raised. It rolls in dust as well as washing, a com- 

 bination of habits rare among birds, and when 

 scratching itself it lowers its wing and raises its foot 

 over it. Some of these minor habits may have 

 significance, but this is not obvious ; what is obvious 

 is that they are common to all Sparrows, and are 

 often group-characters ; thus, all the vast group of 

 generally small birds the Passerines, of which the 

 Sparrow (Passer) is type and name-father seem 

 to drop a wing when scratching. Habits of this 

 kind do not alter even in captive birds, although 

 they may learn strange habits of feeding and nesting, 

 and even alien songs. 



Hence such characters are often useful in classi- 

 ficatipn, just as anatomical characters or inconspicu- 

 ous external ones are of more importance than 

 the general contour. Thus, all anatomists of late 

 years have impressed upon us that the Swallows 

 and Swifts must not be considered near relatives 

 because of their similar forms long-winged, small- 

 footed, and short-billed since these may be ac- 

 counted for by adaptation to a similar life spent in 



