RELATIONSHIPS IN THE ENVIRONMENT 129 



species that make temporary excm'sions from 

 their territories. The male, on its retm'n, flies 

 as a rule direct to its special tree and sings. 

 Sometimes, however, it settles upon the ground, 

 not unfrequently accompanied by the female, 

 and while there remains silent ; but presently 

 rising from the ground and deserting its mate, 

 it flies to the headquarters and sings. Again, 

 nearly every male at one time or another in the 

 course of the season is aroused to action by the 

 intrusion of a rival. The emotional tone of the 

 owner of the territory is then raised, and the 

 intruder is pursued and attacked ; but this alone 

 is not sufficient, it seems as if the chain of 

 instinctive activities, when once aroused by 

 appropriate stimulation, must pursue its course 

 to the end — and the end in such a case is only 

 reached and complete satisfaction only gained 

 when the bird has not merely returned to his 

 " headquarters " but has given vocal expression 

 to his emotion. Finally, we must bear in mind 

 these two facts, that the "headquarters" is 

 occupied solely by the male — it forms no part of 

 the life of the female — and that it is the male 

 only that sings. 



Many such subtle incidents of behaviour as 

 the foregoing can be perceived but not readily 

 described, and trifling though they may seem 

 to be in themselves, yet in the aggregate they 

 yield full assurance of a close relationship. 



The distant song of a male, or the presence 

 of an intruding male, have also stimulating 

 effects, though in somewhat different ways. 



