64 BlCKNELL 0)1 ike Singing- of Birds. [January 



shown to occur. My statement is merely that, as a rule, so far 

 as my own observation has extended, loss of voice in the males 

 of our brilliantly plumaged birds always accompanies loss of 

 other sexual characteristics at the second moult. 



It is sti'ictly true with species of such decided change of plu- 

 mage with the second annual moult as the Scarlet Tanager, the 

 Goldfinch, the Bobolink, and those of our Warblers which un- 

 dergo material change of plumage. 



But many common birds, which show no evident change of 

 plumage with the second moult, have no second song-period. 

 In discussing this class we must remember that it is not always 

 a simple matter to ascertain whether a bird belongs more prop- 

 erly with those species which experience insignificant seasonal 

 changes of plumage or with the reverse class. Among species 

 of obscure plumage it is diflicult to decide what constitutes a 

 decided change. We can conceive how slight changes in certain 

 groups of birds may be equivalent to much greater variation in 

 other groups ; but the relative value of the changes which we 

 may observe is unknown to us. But in that class of singing 

 birds we are now considering, — that class in which the males, 

 without assuming the plainer garb of their mates, 3^et become 

 silent after the breeding season, — the periods of silence and 

 song of all, perhaps, may be accounted for. Let us first discuss 

 summer resident species. Some of these which have no second 

 song-period with us are our earliest departing migrants. Obvi- 

 ously among these there is no opportunity to observe a second 

 song-period in their summer home, even if such takes place. 



Another class of summer residents continue uninterruptedly 

 in song during the greater part of their stay, thus appearing to 

 have no second song-period. But there is little doubt that a 

 period of silence is passed by each individual of such species. 

 For though among its members as a body ihere may be no actual 

 interruption of singing from spring to fall, a time of minimum 

 vocal vigor seems alwavs to follow the breeding season and to be 

 pai'tially recovered from at a later period. In the case of the spe- 

 cies taken as a whole the silent period is obscured by the variation 

 in the singing time of individuals. In other words, there is a 

 suflficient diflerence in the time of the beginning and cessation of 

 song among the component individuals to bridge with isolated 

 songs the true silent period of the sjjecies. Hence the almost con- 



