BICKNELL'S THRUSH 211 



seems to fade away as if in the ensuing silence there might be additional 

 whispered notes which the human ear is not attuned to catch. The 

 refrain is often repeated over and over, the singer seeming to hurry 

 through in order to begin again. Not infrequently the song is begun 

 by uttering the opening measure, but dropped without completion, 

 as a whitethroat breaks off whistling; and conversely, the final part is 

 often given without the prelude, though in many cases this omission is 

 apparent rather than actual, the prelude simply not being audible. 



The complete song, then, may be (inadequately) represented as 

 chook-chook, wee-o, wee-o, wee-o-ti-t-ter-ee. This can be approxi- 

 mated by whistling through closed teeth, but the syllables are hard 

 to distinguish, the many intertwining reverberations merging the notes 

 inseparably. Little variation in the character of the song was noted 

 in the Mansfield region, but judged by the accounts of other observ- 

 ers there may be some regional differences in other habitats. And, 

 needless to say, word descriptions are hopelessly inadequate for giving 

 a faithful picture of the technical character of the song. 



Perhaps the most remarkable feature of the Bicknell's singing is 

 its elaborate flight song, which, strangely, seems to have escaped the 

 notice of the many early observers. Every evening during the height 

 of the breeding season these thrushes indulge in flight performances 

 over their respective territories, singing fervently on the wing. The 

 flight songs start just after sunset (at about 8:20 p. m., E. S. T., 

 early in June), when the light is dim and the woods full of shadows, 

 and last for only 10 to 15 minutes, when darkness puts an end to all 

 singing. In character the flight song is practically identical with the 

 perching song, except that it is usually more hurriedly and breath- 

 lessly delivered. There is often a concentration of singers in a small 

 area, so that the notes of several singers may be mingled. Though 

 the birds probably have individual territories, the boundaries seem 

 not to be strictly observed during flight singing, and shadowy forms 

 drift from place to place, perching momentarily on trees, rocks, or 

 stumps, and then take wing again. Flight singing is spread to some 

 extent over the whole season of song but reaches its maximum develop- 

 ment early in June before incubation is begun. This suggests a 

 primarily prenuptial function. 



Bicknell's thrushes exhibit a fairly definite daily and seasonal cycle 

 of song, the latter correlated with nesting activities. Singing begins 

 in the early dawn (before 3 : 00 a. m. on Mount Mansfield in June) 

 but is somewhat fitful at this time, presumably because the birds are 

 preoccupied with feeding as soon as it is light enough; and by the 

 time a good meal is secured it is too light for optimum song produc- 

 tion. During the prenesting season early in June, songs continue 

 throughout the day, especially in misty weather, but by mid-June 



