HOW BEHAVIOUR IS DETERMINED 21 



Missel-Thrush, perched upon the topmost 

 branches of the elm, persistently repeats its few 

 wild notes ; and the Swallow returns to the barn. 

 All of this we observe each season, and our 

 thoughts probably travel to the delicate piece of 

 architecture in the undergrowth, or to the hole 

 excavated with such skill in the tree trunk ; to 

 the beautifully shaped eggs ; to the parent birds 

 carrying out their work with devoted zeal — in 

 fact, to the whole series of events which complete 

 the sexual life of the individual ; and the attach- 

 ment of a particular bird to a particular spot is 

 readily accounted for in terms of one or other 

 of the emotions which centre round the human 

 home. 



But if this behaviour is to be understood 

 aright ; if, that is to say, the exact position it 

 occupies in the drama of bird life is to be 

 properly determined, and its biological signifi- 

 cance estimated at its true value, it is above all 

 things necessary to refrain from appealing to 

 any one of the emotions which we are accus- 

 tomed to associate with ourselves, unless our 

 ground for doing so is more than ordinarily 

 secure. I shall try to show that, in the case of 

 many species, the male inherits a disposition to 

 secure a territory ; or, inasmuch as the word 

 "secure" carries with it too much prospective 

 meaning, a disposition to remain in a particular 

 place when the appropriate time arrives. 



If the part which the breeding territory 

 plays in the sexual life of birds is the important 

 one I believe it to be, it follows that the 



