PASSERINE BIRDS OF NEW YORK 101 



bird which at one or the other of these three periods of moult 

 becomes indistinguishable from the adult and may be so classed. 

 It is well to grasp the idea that the flight-feathers may out- 

 wear two or three sets of body feathers and a bird does not 

 really attain full adult dress until the former are replaced. In 

 most, if not all cases where mixed plumages are seen during the 

 breeding season, they do not represent birds of different ages 

 but illustrate individual variation at the first prenuptial moult. 

 Unmixed plumages — adults and young being of uniformly dif- 

 ferent colors like the Purple Finch {Carpodacus piLvpurciis) — 

 are presumptive evidence that no prenuptial moult occurs. 



I have occasionally seen birds still partly in immature dress 

 after the moult at the end of their first breeding season as may 

 be determined by left-over feathers, but these birds usually 

 show a plumage so nearly of the adult type as to suggest that 

 they are exceptions in which there has been some individual 

 lack of vitality. Unfortunately we have no other available 

 guide except plumage to determine whether a bird is one, two 

 or more years old and moreover there is a great dearth of 

 winter specimens from the tropics showing while fresh the 

 changes produced by the prenuptial moult. Summed up, there 

 are three periods of moult at any one of which a young bird 

 may assume full adult plumage, the postjuvenal, the first pre- 

 nuptial and the first postnuptial, and prior to each of them the 

 plumage may be immature and made up of feathers which have 

 grown at different periods. These successive plumages follow 

 each other with the regularity of the seasons and will be more 

 fully discussed under the following section. More light is needed 

 on some species, but whether the immature dress requires one 

 moult or two or three to convert it into adult plumage is im- 

 material and does not alter one whit, the fact that it is lost and 

 replaced by actual moult at definite periods. 



IV. SEQUENCE OF PLUMAGES AND MOULTS 



The relation between plumages and moults is so perfectly 

 definite and at the same time has been so little comprehended 



