GENERAL SUMMARY AND CONCLUDING REMARKS 



their offspring by the parents, and the numbers of unpaired 

 individuals of both sexes. On the other, we can detect in the 

 search for new quarters, which necessarily follows the banish- 

 ment of one individual after a conflict with a rival, the 

 inception of a movement which must ultimately lead to an 

 extension of breeding range, and possibly form the foundation 

 of those extensive journeys undertaken each spring for the 

 purpose of procreation. If the struggle for territory were 

 confined solely to the males of the same species, it would 

 be sufficiently interesting, but it becomes more so when we 

 recollect that the males of closely related forms contest the 

 question of ownership with one another. Such racial strife 

 is more frequent than one might suppose to be the case — 

 in fact it is only within recent j^ears that close observation 

 has revealed how common is that which previously I deemed 

 of rare occurrence, and it is not difficult to imagine what 

 far-reaching' effects this extension of territorial warfare may 

 have had on the past history of bird life. 



With the advent of a female in the territory of a given 

 male we witness the commencement of the period of sexual 

 activity, productive of such striking emotional behaviour. 

 This emotion is expressed by movements of the wings, tail, 

 and feathers, and by extravagant antics correlated in some 

 instances with an extravagant use of the vocal powers. 

 Generally speaking, each species has a definite type of 

 response which is peculiar to all its members, but we can 

 often observe a great similarity, or even identity, in the overt 

 expressional movements of different species. We have the 

 slow flapping flight ; we have, without actual flight, the 

 rapid fluttering of wings, the slow flapping of wings, the out- 

 spread motionless wings ; we have the outspread tail, and the 

 sidelong motion of the tail. All of these movements — and 

 others might be added — characterise the emotion which 

 accompanies the sexual instinct. A consideration of these 

 activities led to some discussion of the theory of sexual 

 selection and the modifications of that theory, which from 



