Chap. 36 



CONTOUR y/^'ffc'?f?^fS 



BIRDS CONQUEST OF THE AIR 



shaft 



733 



STRUCTURE Or A 

 CONTOUR FEATHER 



FILOPLUME 



BRFSTLE 



Fig. 36.4. Types of feathers. Left, the contour feathers provide the main cov- 

 ering of the bird, estabhsh the outUnes of its figure, and are the flight feathers of 

 wings and tail. Down feathers are air traps that provide insulation for nestling 

 birds and for older ones of certain kinds, notably the water birds. Filoplumes or 

 thread feathers are down feathers without the loose barbs that create the down, 

 the feathers that are singed off the chicken before cooking. Bristles are wiry 

 feathers about the mouths of the phoebe and other flycatchers. Right, detail of 

 a contour feather. Strength is secured by barbs interlocked by barbules. (Left 

 and upper right, courtesy, Storer: General Zoology, ed. 2. New York, McGraw- 

 Hill Book Co., 1951. Lower right, courtesy, Rand: The Chordates. Philadelphia, 

 The Blakiston Co., 1950.) 



against the dried cell membranes; some are absorbed by the pigment; others 

 are shattered and the surface appears blue. The same feather appears dark 

 gray in direct light because the rays pass through the dark pigment and the 

 black is predominant. In reflected light the physical effect of structure is pre- 

 dominant. 



There are two general kinds of pigment: melanin— blacks, browns to dull 

 reddish, all in minute granules soluble in acid; and lipochromes — pure yellow 

 and pure red, soluble in alcohol or ether. Combinations of different melanins 

 give the blue gray of the chickadee; those of lipochromes the orange of the 

 Baltimore oriole. The iridescence in the neck feathers of pigeons is due to the 

 pigment granules in the feather tips being perfectly spherical so that light 

 striking against them is broken up and rainbow tints produced. 



Molting. This is a gradual, systematic process during which no part of the 



