538 



AMERICAN FORESTRY 



tracts. Between the feather tracts, which are apparently 

 regvilar in every species of hird, there are extensive bare 

 areas which are dependent upon the overlapping of the 

 feathers of adjacent tracts for protection. In the young of 

 most birds, until the feathers are matured, the feather 

 tracts ( pterylas ) and the naked spaces (apteria) are very 

 conspicuous. The sickly chickens appear so naked because 

 the bare spaces are entirely exposed by the scarcity of 

 feathers in everv tract. 



A MOLTING SPARROW 



Showing the replacement of feathers. The new feathers appear darker than 

 the old and include all but three of the primaries, one secondary, the wing 

 coverts and a few feathers on the back. Several of the central tail feathers 

 have been lost but not yet replaced. 



Most birds molt but once a year, but it would obviously 

 be impossible for a bird that changes to a dull coat after 

 the nesting season to assume its brilliant breeding plumage 

 without another molt in the spring. Thus we find in the 

 case of the scarlet tanager, goldfinch, liobolink and other 

 brilliantly colored species that the males undergo a spring 

 or " pre-nuptial " molt as well as a fall or "post-nujitial " 

 change of plumage. The pre-nuptial iimlt is usually in- 

 complete, however, as the wings and tail feathers, which 

 are dull even in brightly colored birds, are made to serve 

 both plumages. 



In some birds, however, where there is a conspicuous 

 change in color from the winter to the breeding plumage, 

 it is accomplished in another way known as " feather 

 wear." This is possible because each feather is tipped 

 with a color different from the main portion of the plume. 

 The feather tips give the general color to the fall and 

 winter plumage, but as they wear off, the underlying 

 breeding color is exposed. Browns, yellows and grays 

 occur most frequently as color-tips with blacks, browns 

 or reds beneath. The robin"s breast becomes much redder 

 with the advance of spring because the gray tips of the 

 feathers wear off. The black spot on the throat of the 

 house-sparrow and that on the breast of the meadowlark 

 treble in size. The red-winged blackbird loses his red- 

 dish-brown cast and becomes intensely black, while the 



snow bunting wears away the dusky from its head and 

 breast and shows snowy white. 



In birds like the purple finch and indigo bunting, where 

 there are no apparent gray tips to the feathers and which 

 still seem to become more intensely colored as the season 

 advances, the feather wear is of a different sort. It was 

 fonnerly believed that the feathers became repigmented 

 from the blood of the bird but to-day that is considered 

 impossible, because once the feather is mature, it is a dead 

 structure, physiologically disconnected from the bird's 

 body and serving only in a mechanical way for flight and 

 protection. To understand what actually happens in the 

 case of these birds, it is necessary to know something of 

 the structure of a feather as shown under the lens. 



All feathers are composed of a mid-vein or shaft and 

 the web. If the web is examined carefullv it will be seen 



A PAIR OF HOUSE SPARROWS 



These birds are in their summer plumage. The sparrow has no spring molt, 

 but by the wearing away of the gray tips of the feathers a considerable change 

 in color ensues, especially on the throat of the male. 



to be composed of a series of fibers called '" barbs " 

 attached on each side of the shaft. Each barb, similarly, 

 bears rows of small barbules. When these barbules are 

 examined under the microscope they are found to bear 

 a number of minute recurved booklets which fasten into 

 the booklets of adjacent barbules and give to the feather 

 its firmness, being best developed in the wing feathers, 

 which require the greatest strength. Some feathers and 

 the innermost parts of most feathers lack this device and 

 are therefore always soft and fluffy, giving little resistance 

 to the passage of air through them. Now in the case of 

 the purple finch and indigo bunting, the red and the blue 

 colors are located mostly in the barbs while the barbules 

 and booklets are dusky. With the wearing away of the 

 hooks and the barbules on the body feathers, the barbs 

 become more conspicuous and the color of the bird 

 becomes apparently more intense. 



