PASSERINE BIRDS OF NEW YORK 109 



as for example in the Song Sparrow (Melospiza fasciata], or 

 Bluebird (Sialia sialis), or a prenuptial moult, usually partial 

 sometimes complete, takes place evidently for the purpose of 

 supplying a portion at least of the bright feathers of the adult. 

 In the plumage of the first winter males and females may usually 

 be told apart for the first time and the tendency is for males in 

 this dress to resemble, although brighter in color, the adult fe- 

 male in winter dress. There is however great individual varia- 

 tion, some males assuming here and there few or many feathers 

 fully adult in pattern and color. It is fair to suppose such birds 

 to have unusual vitality and mere precocity must not be confused 

 with what generally takes place. Then there is the other ex- 

 treme where a bird fails to reach the standard and a deficiency 

 of pigment or failure to moult the Juvenal feathers occurs ; and 

 it requires a great many specimens to be sure of what the nor- 

 mal acquisitions really are. As a general rule the depth of 

 color in the wings and tails of young birds will average less than 

 that of adults, and in some species this character becomes more 

 pronounced the longer the plumage is worn. The increasing 

 depth of color apparent in some species while they are assuming 

 first winter plumage, is I think, largely due to superimposed 

 layers of new feathers. 



The small size of the bill of young birds is a character dis- 

 tinguishing them from adults for a long time and a deepening or 

 change in its color is marked in some species. The color too 

 of the iris is sometimes strikingly different in young birds and 

 helps determine their age. The change during the winter from 

 brown to red in the iris of the Red-eyed Vireo ( Vireo olivaceus) 

 and from gray to white in the White-eyed Vireo, ( Vireo nove- 

 boracemis) is only somewhat more striking than what occurs in 

 many other species. Legs and feet also deepen in color. 



About nine out of ten birds in most collections are in first 

 winter plumage, and it is one that ought to be thoroughly un- 

 derstood. 



4. First Nuptial Plumage (plate IV, fig. 3 ; plate VI, fig. 3 ; 

 plate VII, fig. 4). This is a fourth stage representing the dress 

 assumed by young or immature birds during their first 



