° 1918 J Hawkins, Sexual Selection and Bird Song. 431 



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 prog- 

 ress or before the complete maturity of their renewal plumage 

 but birds may be found sitting upon their eggs with evident indi- 

 cations of activity on 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 it 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 

 undergoes its moult in August. The growth of the new feathers 

 continues 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 

 explanation. 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 

 its 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- 



