1SS4.I BiCKNELL 0)1 the Singhig of Birds. I 2Q 



covered with growing feathers and without fat. In mid- Septem- 

 ber some, at least, show a nearly perfected j^lumage, with areas 

 of fat beginning to accumulate ; and individuals may be found 

 almost a month later with the renewal of plumage still incom- 

 plete ; such, perhaps, are birds of the year. It would appear 

 from these facts that the impulse to song is iirst interrupted by 

 the moult, and further suppressed by the supervening adipose 

 condition. 



Turdus fuscescens. Wilson's Thrush. 



Contrary to what we find to be true of most of our summer 

 birds, the Wilson's Thrush seems often to remain silent for some 

 days after its arrival in the spring ; although this is not invariably 

 the case. 



Though it comes to us but little later than the Wood Thrush, 

 its song in some years may not be heard until two weeks after 

 that of the latter bird ;■ and yet we lose it fully a month earlier. 

 With the Wilson's Thrush singing continues regularly through the 

 month of June and into the early part of July, but after this time is 

 not commonl}^ heard, and soon has entirely ceased. For several 

 years dates of final'songs have been entered in my books between 

 July 10 and 15 ; though a single song may sometimes be heard 

 later in the month. July 21, 22, and 26 are the latest dates that 

 I have recorded. Often in the first, or even second week of 

 July, though singing is so soon to cease, the vocal impulse seems 

 to be at its height, and our thick swamps and low woods sound 

 with the continually reiterated songs of numbers of these fine- 

 voiced Thrushes. These birds are so much oftener heard 

 than seen that after they li^ve become silent they are not often 

 observed : but not until the end of September have the}^ all left 

 us. 



By the end of August the plumage has been renewed and the 

 birds are very fat. But specimens maybe taken at this time, and, 

 indeed, through September, showing a slight activity of feather- 

 growth. 



Turdus ustulatus swainsoni. Olive-backed Thrush. 



This Thrush is in full song during its spring migration, which 

 occupies the latter half or two-thirds of May, but is commonly 



