ISOLATION LEADS TO EXPANSION 285 



the impulse to seek isolation ceases for a time 

 to dominate the situation. The inference, there- 

 fore, is that atmospheric changes bear some 

 relation to the functioning of the instinct ; but 

 whether it be temperature, or humidity, or the 

 direction and velocity of the wind, or a combina- 

 tion of two or more of these factors that supplies 

 the stimulus, we cannot tell. 



The appropriate organic condition and the 

 stimulus have then still to be determined, and 

 we must pursue our inquiry from the point at 

 which the impulse comes into functional activity. 

 We will take a simple case, and one free from 

 complication. 



Let us suppose that there is an area bereft 

 of bird life, if it can be so imagined, but in 

 proximity to other inhabited areas. Into this 

 area, whilst in search of isolation, let us imagine 

 that a Yellow Bunting finds its way. After the 

 manner of its race it establishes a territory and 

 occupies, let us say at a low computation, half an 

 acre of ground. It then obtains a mate, breeds, 

 and rears offspring, two of which we will assume 

 are males. Reproduction ended, the birds desert 

 the area, and in the following spring, when the 

 impulse again asserts itself, parents and offspring 

 seek again their former haunts. We now have 

 three males, each of which occupies half an acre, 

 and each of which rears two offspring — that is the 

 position at the close of the second year. In the 

 third year the number will have increased to 

 nine and the area occupied to 4^ acres ; and so 

 on in succeeding years, until by the beginning of 



