8 INTRODUCTION 



recourse to so complex a principle of explana- 

 tion, and that by the law of habit formation. 

 In common with other animals, birds are 

 subject to this law in a marked degree. An 

 acquired mode of activity becomes by repetition 

 ingrained in the life of the individual, so that 

 an action performed to-day is liable to be 

 repeated to-morrow so long as it does not pre- 

 judice the existence or annul the fertility of the 

 individual. 



Let us see how this may have operated in 

 determining the limits of the area acquired, and 

 for this purpose let us suppose that we are 

 observing a male Reed- Bunting recently estab- 

 lished in some secluded piece of marsh land. 

 Scattered about this particular marsh are a 

 number of small willows and young alder trees, 

 each one of which is capable of providing plenty 

 of branches suitable for the bird to perch upon, 

 and all are in a like favourable position so far as 

 the outlook therefrom is concerned. Well, we 

 should expect to find that each respective tree 

 would be made use of according to the position 

 in which the bird happened to find itself. But 

 what actually do we find — one tree singled out 

 and resorted to with ever-increasing certainty 

 until it becomes an important point in relation 

 to the occupied area, a headquarters from 

 which the bird advertises its presence by song, 

 keeps watch upon the movements of its 

 neighbours, and sets out for the purpose of 

 securing food. We then take note of its 

 wanderings in the immediate vicinity of the 



