62 BlCKNELL Oil the Singing of Birds. [January 



In many cases the moulting periods of our Song-birds corres- 

 pond more or less closely with periods of silence, voice being 

 resumed with the renewal, of plumage. The general statement 

 may therefore be made, that birds are predisposed to"wards silence 

 during the height of the moult. Though this fact may be by 

 many regarded as one not requiring demonstration, it is by no 

 means without exceptions. In the earlier and later stages of the 

 moult the vigor of birds in general seems little impaired. Not 

 only do many species enter on their migration while yet the moult 

 is in progress or before the complete maturity of their renewed 

 plumage, but birds may be found sitting upon their eggs with 

 evident indications of activity in the growth of feathers. Still we 

 must regard it as a general fact that singing and moulting are in 

 some degree complementary. 



But the loss and renewal of plumage in its resulting tendency 

 of interference with the use of the vocal organs may be superse- 

 ded by a counter influence which at times arises in the special 

 seasonal development of the sexual orga]\s. Thus birds in the 

 spring are sometimes in song before their new plumage has at- 

 tained its full growth, and it is probable that this is normally the case 

 with many species. But cases of birds in full voice while under- 

 going their second semi-annual moult, when the sexual functions 

 are inactive, appear to be uncommon, perhaps exceptional, unless 

 the growth of plumage be almost completed.* 



it would seem to follow that the times of migration are in many cases regulated if 

 not determined by the times of the moult. As the times of this process are 

 variable witli different species, it seems highly probable that a study of the subject 

 would shed light on the causes of the different times of migration of allied species 

 of birds. It is clear that the periodical mutations of the plumage of birds is in- 

 volved directly or indirectly with much in their lives that we now but imperfectly under- 

 stand — with their migrations, their distribution, their breeding habits. And it would 

 not be going too far to claim for the moult adirect bearing on classification, for different 

 species, and in all probability different families and genera, moult in different ways. 

 The subject cannot be followed further here, but it is safe to assume that its careful 

 study would lead to important and unexpected results. It may not be untimely here to 

 suggest that in recording the condition of the moult or renewal of the plumage of birds 

 great care must be exercised to distinguish between the sexes and ages of specimens 

 examined. Often adult and juvenile individuals of a species will at the same time be 

 found to present great differences in the relative maturity of their plumage, and, in less 

 degree, males and females, as well as individuals of the same sex, will be found to 

 differ. 



* As bearing upon this topic I learn from Mr. C. Y. Holden of New York, the well- 

 known bird-fancier and importer, that while many Canaries become disinclined to 

 sing, or even entirely silent, during the moult, some of the finer breeds sing uninterrup- 

 tedly during that period. 



