BIRD SONG HAWKINS. 469 



with the renewal of plumage. The general statement may therefore 

 be made that birds are predisposed toward silence during the height 

 of the moult. Though this fact may by many be 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 the birds in 

 general seems little impaired. Not only do many species enter on 

 their migrations while yet the moult is in progress or before the 

 complete maturity of their renewal 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. 



Some birds have no second song period. The catbird sings from 

 April through July, but is not heard in the autumn. The brown 

 thrasher sings from April to the first week in July, but is silent in 

 October. After August the scarlet tanager is not heard again in 

 full song. Where this second period is lacking it is probably due 

 to the excessive fatness of the bird. Thus the scarlet tanager un- 

 dergoes its moult in August. The growth of the new feathers con- 

 tinues until October, when the bird becomes very fat. The wood 

 thrush moults in August, but is not fat. By the last of September 

 its plumage is nearly perfect and the bird is fat. Hence the song 

 seems to be interrupted first by the moult and then by the adipose 

 condition. 



There are some cases where the birds' best song is outside of the 

 mating season. It is a significant fact that the male birds arrive 

 first in the migration and soon after their arrival begin their full 

 song, though there are no females to hear. It may be said this is 

 for the purpose of attracting the females on their arrival or that 

 the male is practising his art, but this seems too superficial an ex- 

 planation. There must be something within the bird himself which 

 causes him to sing, though there is no ear to listen. Hudson calls 

 attention to a small yellow field finch of La Plata which does it best 

 singing in August. There birds gather in great flocks in the tops 

 of trees and sing in concert, producing a " great volume of sound, 

 as of a high wind when heard at a distance." Later this choir 

 breaks up, love infects the individuals, and they scatter over fields 

 and pasture lands. But during courtship the male has only a feeble, 

 sketchy song. 



There are birds which sing more or less the entire year. Hudson 

 found several birds in Patagonia with good voices, one a mocking- 

 bird, which were autumn and winter songsters. Olive Thorne 

 Miller tell of a gray-checked thrush in captivity which sang all 

 winter. 



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