412 The Outline of Science 



no means confined to those which are gregarious at other times; 

 conversely, it is also true that some birds which at other seasons 

 band together are among the least social at this special time. 

 More than one factor is probably involved : the scarcity of suitable 

 sites for marsh-fowl, for example may be a reason for concen- 

 tration in special spots, and strength of defence against enemies 

 may often be an advantage gained. In other cases the problem 

 of food-supply will tend to produce distribution rather than con- 

 centration, and this is especially the case with many of the smaller 

 species of our common birds : among warblers, for example, there 

 is a marked tendency for a pair to select a small territory within 

 which they will remain and from which they will endeavour to 

 exclude all other members of their own species and even, in due 

 course, their own young. 



Many birds, like human beings, would seem to enjoy the 

 company of their kind. The gregarious habit is common, for 

 example, among rooks, starlings, pigeons, swallows ; parrots roam 

 in bands, apparently for the pleasure of one another's company. 



We may have crowds and associations, however, without 

 sociability; a community of separate individuals may exist with- 

 out there being any corporate life or power of acting as a unity. 

 Still, we do see many instances of a capacity for unified action and 

 distinct features of a social life. "There appears to be an intel- 

 lectual advantage in sociability, if we may argue from the fact 

 that many social animals show a high development of wits. The 

 three cleverest kinds of birds are rooks, cranes, and parrots, and 

 they are notably social. There is, of course, the danger of putting 

 the cart before the horse, for it may be that the sociability is in 

 part the expression of good brains. It may also be argued that 

 the non-gregarious crow is just as clever as the social rook, and 

 many analogous instances might be given." 



The Rook is the best example of our gregarious birds. There 

 is no doubt that the members of the Crow family have fine brains, 



1 Professor J. Arthur Thomson, The Wonder of Life. 



