GROWTH AND DEVELOPMENT 81 



feathering progresses up toward the sides and flanks and down toward the median line of 

 the keel. Feathering on the breast begins at the upper forward parts and progresses down- 

 ward toward the belly. On the neck it progresses from the crown toward the back and from 

 the chin to the breast, the front centerline of the throat being the last to close in. The 

 wing coverts are fully developed in advance of the flight and the body feathers, the upper cov- 

 erts being completed before the lower. 



The head region is the last to be completed. While two or three pinfeathers may be ob- 

 served in the crown at two weeks of age, down remains in the auricular region and chin until 

 the bird has completed the change to the juvenal plumage over the rest of the body. The first 

 to appear on the head are the elongated crest feathers. The succession progresses from 

 front to back on top of the crown then down toward the eye. The forehead and upper aur- 

 icular region are filled in simultaneously with all feathers appearing at about the same time. 



As a general rule, it may be said that the succession of feathering progresses in the direc- 

 tion in which the feathers lie. It is well to remember, however, that development begins al- 

 most simultaneously in each of the topographical regions as outlined in the foregoing. By 

 the time the chick is two weeks of age, pinfeathers of the juvenal plumage appear in all of 

 these regions. 



The replacement of juvenile by adult plumage as well as the annual renewal of feathers in 

 mature birds is followed in the same relative order. While there may be some variation among 

 the individual birds, it follows in general the pattern and succession as that from natal to 

 juvenile. 



Adult Plumage 



This is the plumage attained by the mature birds in the fall. If a line or division can he 

 drawn between the end of the juvenile and the beginning of the adult plumage, it might well 

 be established at seven weeks of age, for by this time the tail has attained its growth and the 

 feathering on the head is complete. While down is still present in certain regions notably 

 on the upper thigh, lower sides of the rump, forward of the scapulars and portions of the 

 upper breast, mature plumage is in evidence over most of the body. At this age many pin- 

 feathers can be seen protruding from the skin with the juvenile feathers appended to the tip 

 of the sheath. These pinfeathers may be recognized as the adult plumage by their pigmenta- 

 tion; some being white, others rufous or gray. It was noted that the juveniles remained ap- 

 pended in the same manner as the natal down was appended to them. This was observed 

 in all regions except in the flight feathers and the tail. 



The adult plumage, however, does not approach completion until the bird attains the age 

 of 18 to 20 weeks, ahhough this is subject to some variation. At the Research Center most 

 of the birds had acquired their mature plumage by October first. 



But even in the fall the plumage cannot be considered as fully complete since new feathers 

 continue to grow as the season progresses, and probably do so well into mid-winter. As the 

 temperature decreases during the winter months it may be noted that the feathers are much 

 tighter and more closely interlocked than during the fall. At this time all of the spaces are 

 concealed by a thick mat of feathers. 



By the time s|)ring arrives a slight change in coloration is evident, particularly in the head 

 region, due not to moult but to feather wear. As the season advances, however, certain feathers 

 are moulted about the body. It may be noted that such feathers are dropped from areas ad- 

 jacent to the spaces and a slight thinning of feathers occurs all over the body in general. It 



