130 DWIGHT 



VII. PLUMAGES AND MOULTS OF NEW YORK 



SPECIES 



Classification of Moult 



No attempt has ever been made to group North American 

 birds according to the manner of their moulting and it is cer- 

 tainly desirable that an outline of some system of classification 

 should be traced, imperfect as is our present knowledge of the 

 subject. Among the Passerine species of New York, which 

 include nearly all of those of eastern North America, will be 

 found the greatest diversity of moult not only in the different 

 species, but in individuals of the same species, not to mention 

 the peculiarities due to the age and sex of these individuals. 

 Large series of birds taken at the proper season are necessary 

 to determine which are the exceptions and which the rule, and 

 until more positive light of this nature is thrown upon the 

 species that moult when south of the United States, the status 

 of some of them must remain a matter of doubt. 



Aside from ascertaining the facts of moult in each species, the 

 greatest difficulty lies in the impossibility of drawing any hard 

 and fast line between groups or classes that may be proposed. 

 The only invariable moult is the postnuptial which, except in a 

 very few rare cases, is absolutely complete and takes place in all 

 species at the close of or soon after the breeding season peculiar 

 to each. The dividing line, however, between species with a 

 postnuptial moult only and those that undergo a prenuptial as 

 well, is not a definite one. Some appear to undergo only one 

 prenuptial moult, that of the first year of their life, and form a 

 connecting link between groups of birds that moult annually 

 and those that moult twice a year, but as the females of such 

 species usually omit the prenuptial changes of the male, it 

 seems advisable to consider them all as a special class of birds 

 moulting annually. 



As in plumage so in moult, classification must depend pri- 

 marily upon the males and the extent of their prenuptial changes 

 seems to afford a good basis for classifying birds with semi- 



