10 INTRODUCTION 



to a particular environment, is an important 

 factor in the situation. For example, if instead 

 of resting content with just a bare position 

 sufficient for the purpose of reproduction, the 

 Guillemot were to hustle its neighbours from 

 adjoining ledges, the Guillemot as a species 

 would probably disappear ; or if instead of 

 securing an area capable of supplying sufficient 

 food both for itself and its young, the Chiffchaff 

 were to confine itself to a single tree, and, 

 after the manner of the Guillemot, trust to 

 spasmodic excursions into neutral ground for 

 the purpose of obtaining food, the Chiffchaff as 

 a species would probably not endure. All such 

 adjustments have, however, been brought about 

 by relationships which have gradually become 

 interwoven in the tissue of the race. 



The intolerance that the male displays 

 towards other individuals, usually of the same 

 sex, leads to a vast amount of strife. Nowhere 

 in the animal world are conflicts more frequent, 

 more prolonged, and more determined than in 

 the sexual life of birds ; and though they are 

 acknowledged to be an important factor in the 

 life of the individual, yet there is much differ- 

 ence of opinion as to the exact position they 

 occupy in the drama of bird life. Partly 

 because they frequently happen to be in 

 evidence, partly because they are numerically 

 inferior, and partly, I suppose, because the 

 competition thus created would be a means of 

 maintaining efficiency, the females, by common 

 consent, are supposed to supply the condition 



