140 A HISTORY OF BIRDS 



the pugnacity which species which lead solitary lives cunningly 

 exhibit, is due to an inherent moroseness of disposition. As a 

 matter of fact it is rather begotten by stern necessity. An 

 area which would provide an abundance for a pair of birds would 

 spell famine if occupied by a flock, and hence the instinct of 

 self-preservation develops pugnacity. Competition for whatever 

 is to be had results, and the most aggressive species will pre- 

 vail. Yet all this is to be gathered rather by inference than by 

 observation, for this struggle between individuals of the same 

 species, or between two or more allied species of similar habits, 

 is carried on decently, as it were : there is no parade by the con- 

 querors before the public. Consequently, we only realise what 

 has taken place by inference, as a rule. That one gregarious 

 species will invade the territory of another nearly related species 

 and more or less totally supplant it, is shown, for instance, in the 

 case of the Lesser Kestrel, which since 1877 has annually in- 

 vaded the district of Orenberg, Russia, in thousands, displacing 

 the Red-footed Falcon, which has retreated to the northern pro- 

 vinces of Russia. 



Although earlier in this chapter it was suggested that gre- 

 garious species, on the whole, hold their own best, inasmuch as 

 they are numerically stronger than species which lead solitary 

 lives, it may well be that this is not really the correct interpreta- 

 tion of the facts. That is to say, this numerical superiority may 

 be the result of a uniformly abundant food supply, so that the 

 formation of large colonies may be not so much the consequence 

 of the evolution of a sense of comradeship, or of a more or less 

 intelligent sense of the many advantages gained thereby, as of a 

 lessened mortality due to the lightening of the struggle for food. 



Birds, as a rule, do not lay up stores of food for use during 

 times of scarcity, and, strangely enough, the only exceptions to 

 this rule appear to be made in the case of certain Woodpeckers 

 which band together for this purpose. Thus the Californian 

 Woodpecker {Melanerpes forviicivonis) is said to band together 

 in considerable numbers, and, selecting an oak-tree suitable to 

 the purpose, proceed to riddle the bark with holes. This done 

 they set to work to collect acorns which are then thrust each into 

 a separate hole. For some unknown reason only one tree in an 

 area of several miles is selected, and having been duly stocked 

 is left for some considerable time. At irregular intervals 



