THE MOLT 85 



form they fit the bird for locomotion (see beyond, under Uses of the 

 Wing and Tail) or in color adapt it to the special needs of its haunts 

 and habits. In the first place, however, the field student should have 

 some knowledge of the laws of feather change included under the general 

 term of molt. 



The Molt. When hatched, a Passerine bird is naked except for a 

 scanty growth of filmy down on the feather tracts of the upper half of 

 the body. This is the 'natal down' of Dwight ('00) whose terminology 

 I adopt. The natal down is quickly succeeded by the 'Juvenal 1 or nest- 

 ling plumage, which is sufficiently grown in from eight to fourteen days 

 to enable the bird to leave the nest. The tail is still only about half- 

 grown and the wings, as a rule, barely large enough to permit of short, 

 uncertain flight. 



Some birds (e. g. Sharp-tailed and Seaside Sparrows) wear this Juvenal 

 or nestling plumage between two and three months, but most species 

 lose it shortly after leaving the nest. In either case, it is followed by 

 the first winter plumage, which is acquired by molt (postju venal) 

 of all the body feathers, most of those of the wings and tail usually 

 being retained. If the young bird now resembles its parent, their 

 plumage changes are thenceforth the same. 



In the fall all birds molt, but in the spring there is no regularity 

 as to feather renewal, even among closely related species. The Bobo- 

 link and the Sharp-tailed Sparrow have a complete spring molt (pre- 

 nuptial), even to the wings and tail; the Scarlet Tanager and Gold- 

 finch molt only the body feathers; other species acquire some new 

 feathers about the head and chin, and with many there is no feather 

 growth at this season, the differences between the winter and breeding 

 plumages being due to wear or fading. 



After the breeding season, all adult birds pass through a complete 

 molt (postnuptial), and the bird is again in winter plumage. 



In its simplest form, and ignoring the comparatively few cases in 

 which an essentially adult plumage is not acquired at or before the first 

 prenuptial (spring) molt, the molt among the Passeres may be summar- 

 ized as follows: (1) Natal down, lost by postnatal molt which brings 

 the (2) Juvenal or nestling plumage; lost by post Juvenal molt which 

 brings the (3) first winter plumage; lost to a greater or less extent in 

 some species by prenuptial molt which brings the (4) nuptial plumage; 

 lost by postnuptial molt which brings the (5) second and subsequent 

 winter plumages. 



With some minor variations this is the general order of molt among 

 other than Passerine birds. Except the Ducks and Ptarmigan all birds 

 have a complete postnuptial molt, and with many Snipe the spring or 

 prenuptial molt is complete. Some Snipe wear the Juvenal plumage 

 until winter or even until the prenuptial molt, the post Juvenal molt 

 being omitted. 



Among the praecocial Gulls, Terns, Ducks, Shore-birds and Galli- 

 naceous birds the natal down thickly covers the body and the chick 



