INDIVroUAL MOLT. 19 



cal period while it is assuming a now suit of flight feathers. It wouhl seem 

 probable that in cases like these where we have a difl'orent plumage, evidently 

 ancestral because like the female, and worn for a short time after the brcedin"- 

 season; and also like the fall plumages of the Bobolink, Indigo, and Hlack 

 Poll Warl)ler where the same plumage is worn for several months and eventu- 

 ally replaced by a better, we may have instances of the retaining of the older 

 style of plumage of the males for a lesser or longer period according to various 

 influences. The tendency among birds seems to be, especially among the more 

 boreal, to change after the breeding season as quickly as possible and to ignore 

 any spring molting change. 



INDIVIDUAL MOLT. 



As the principal use of feathers is to conserve the body heat, it follows 

 that when a bird is ready to molt, all the feathers cannot be advantageously 

 shed and replaced at once. Consequently there has developed a definite se- 

 quence of change which is best suited to the habits and economy, and which is 

 slightly or greatly different in the various groups, though ordinarily a general 

 similarity is noticeable. Thus, while many ducks can lose all their flight 

 feathers at once, and as a result change their habits for a period, all birds 

 cannot do so just as all ducks do not. This subject cannot be discussed in any 

 great detail here for it is too vast, but a few examples will suffice to show the 

 character of the changes and to some extent their correlation. 



The first sign of a molt, (and this is more generally true of young birds,) 

 is on the breast where the feathers along the sides are usually rapidly re- 

 placed. At the same time, or a few days later, pin feathers will be noticed 

 among tho old feathers of the back so that usually the body feathers are the 

 first to complete the molt. While this is going on the head feathers will be- 

 gin to change, so that we find the molt growing as it were from the body 

 toward the head and from the head downwards. In the ducks and rails, and 

 in some other cases probably, the flight feathers are shed first, the body 

 ohange following immediately, but in many cases the change may go on at 

 once variously over the whole body, except that some parts, such as about the 

 bill, the thighs, the wing and tail coverts, may be the last to perfect the new 

 growth. As the tail in ordinary cases is of little use, it is often dropped at 

 once, though occasionally a few feathers may persist for a time, but, as in the 

 Turkey Vulture the tail is an important flight organ, we find that its feathers 

 as well as those of the wing, as on other species of similar flight habits, are 

 gradually and often irregularly replaced so as not to interfere with the neces- 

 sary constant use of tho organ. A peculiar instance of this obtains in the 

 woodpeckers where the central pair of old feathers are retained until the lat- 

 eral new ones are functionally serviceable. 



