4 INTRODUCTION 



that ; by all those movements, in fact, which 

 the term migration, widely applied, is held to 

 denote. Now the impulse which prompts these 

 travelling hosts must be similar in kind whether 

 the journey be long or short ; and it were better, 

 one would think, to regard such movements as 

 a whole than to fix the attention on some one 

 particular journey which fills us with amazement 

 on account of the magnitude of the distance 

 traversed or the nature of the difficulties over- 

 come. For, after all, what does each individual 

 seek ? There may be some immature birds which, 

 though they have not reached the necessary 

 stage of development, happen to fall in with 

 others in whom the impulse is strong and are 

 led by them — they, know not where. But the 

 majority seek neither continent nor country, 

 neither district nor locality is their aim, but a 

 place wherein the rearing of offspring can be 

 safely accomplished ; and the search for this 

 place is the earliest visible manifestation in many 

 species of the reawakening of the sexual instinct. 

 The movements of each individual are then 

 directed towards a similar goal, namely, the 

 occupation of a definite station ; and this 

 involves for many species a distinct change in 

 the routine of behaviour to which previously they 

 had been accustomed. Observe, for example, 

 one of the numerous flocks of Finches that 

 roam about the fields throughout the winter. 

 Though it may be composed of large numbers 

 of individuals of different kinds, yet the various 

 units form an amicable society actuated by 



