RELATIONSHIPS IN THE ENVIRONMENT 127 



yet in no single instance did I hear the true song 

 uttered on the feeding ground, althougii the 

 moment a male returned to its territory its 

 monotonous croak could be heard, uttered more- 

 over with that persistence which is so marked 

 a feature of all song or of the sounds that 

 correspond to it. 



Thus it will be seen that, even after the 

 internal organic changes have taken place, 

 the instinct of song is not susceptible to 

 stimulation at all times and under all circum- 

 stances, but only at certain specified times 

 and under special circumstances which can be 

 observed to correspond with the occupation of 

 the territory. 



In many species each male singles out 

 within its territory some prominent position 

 to which it resorts with growing frequency. 

 This position is an important feature of the 

 territory, and exercises a dominating influence 

 on the life of the bird. I have referred to it 

 as the " headquarters," and it may be a soli- 

 tary tree or bush, an outstanding mound or 

 mole hillock, a gatepost or a railing — any- 

 thing in fact that supplies a convenient 

 resting place so long as it fulfils one condition, 

 namely that the bird when it is there is con- 

 spicuous. It need not, however, be a tree or a 

 mound or indeed anything upon which the 

 bird can perch, for there is reason to think 

 that the soaring flight undertaken at this 

 season by so many males, since it is generally 

 accompanied by the specific sexual sound, 



