132 RELATION OF SONG TO THE TERRITORY 



when it is joined by a female a change becomes 

 apparent ; instead of the incessant trill, there 

 are spasmodic outbursts of short duration, and 

 in the course of a few days the bird lapses into 

 a silence which may be broken for a short while 

 at dawn, or late in the evening, but is often 

 complete. More striking still is the change in 

 the case of the Marsh- Warbler, and the sudden 

 deterioration, or even suspension, of strains so 

 beautiful and so varied, at a moment, too, when 

 it might least be expected, at once arrests the 

 attention. The Reed- Warbler that had its 

 headquarters in a willow sang vigorously from 

 the middle of May until a female arrived on 

 the 20th June, when its voice was hushed, except 

 for occasional outbursts which lacked force 

 and were of short duration. When the Wood- 

 Warbler secures a territory it repeats its sibilant 

 trill with unwearying zeal, yet no sooner does 

 a mate appear than its emotion is manifested 

 in other directions. The Heed-Bunting is 

 vociferous during February and March ; but 

 when a female arrives, periods of silence are 

 frequent and the instinct of the bird becomes 

 progressively less susceptible to stimulation. 

 After the manner of the race the male makes 

 temporary excursions from its territory accom- 

 panied by his mate, and it is noteworthy that 

 when he returns and she is absent he sings, 

 but that the moment she joins him, or even 

 comes into sight, he is silent. In fact, in greater 

 or less degree, a change is noticeable in the 

 song of many resident and migratory species 



