1SS4.1 15icKM'".i.f. on the Singing- of B/r(/s. 6 I 



tinct sciisons of sonii,-. separated by a greater or less interval of 

 silence. 'The lirst of these song-periods is that of the spring 

 migration and the breeding season ; the otlier a period \ ariable 

 as to time and duration with dilTerent species, but which may in 

 general be said to succeed a time of silence which follows the 

 breeding season, with some species continuing tlnough their 

 return migration from their breeding grounds. The greatest 

 variation, however, with respect to its separation from the first 

 song-period, the constancy, the extent and the time of the latter 

 song-period, is exhibited among its exponents, as will be shown 

 bevond. 



Some of our summer resident birds cease to sing at the close of 

 or soon after their breeding season, and are silent during the re- 

 mainder of their stay. Others discontinue song with domes- 

 tic duties, but resume it before their departure after a longer 

 or shorter period of more or less complete silence. Still others 

 continue uninterruptedly in song during the greater part of their 

 sojourn. This much having been said, it becomes proper to 

 inquire into the causes which produce these results. 



Perhaps as a factor in sexual selection we perceive the chiet 

 office of song in the avian economy ; its main purpose is thus sub- 

 served diu-ing the mating and breeding season. Thereafter song 

 is not longer a necessity, and the inference would be natural that, 

 after the enervating duties of this period, the vocal organs would 

 be allowed to rest. But disuse of the vocal organs does not result 

 from this cause. It is even true that those species whose family 

 cares are lightest, that rear a single brood onl}-, first become 

 silent ; those that bring up two or even three families being least 

 readv to abandon song. Apart from the dominating influence 

 of the breeding season, that which most directly governs the 

 singing-times of birds, and, I may add in passing, their seasonal 

 movements, their breeding seasons and the number of broods 

 reared, is undoubtedlv their periodical loss and renewal of 

 plumage.* 



* The relation between the moult and the migration of birds is a subject demanding 

 the most careful study. It is indeed surprising that the connection between such 

 obviously related phenomena has not long since been worked out. While it is true 

 that many birds enter upon their migration with the growth of feathers still active in 

 parts of their plumage, it is also undoubtedly true, as a general fact, that the moulting 

 season is a time of inactivity and thus adverse to extended migration. Many birds 

 migrate just before or shortly after the new plumage has completed its growth. Hence 



