INTRODUCTION. 5 



a few weeks, as in the eiders (Somaterice), but we have, on the other hand, examples 

 of the reverse, as in the ptarmigans (Lagopus), some of which, at least, show the 

 peculiarity of a permanent molt during the whole summer. Many birds retain the 

 first plumage during the first winter of their life, while others change it a short time 

 after they have put it on; and in some for instance, in the grouse family even the 

 wing-feathers are shed before the first winter sets in. Very frequently the new plu- 

 mage has a color quite different from the one which was thrown off, and particularly 

 Avhere two molts occur, the seasonal change in the color of many birds is thus 

 accounted for. But there are a whole category of cases in which a radical change in 

 the coloration according to season is effected without the feathers being molted. In 

 many birds, notably among the Passeres, the feathers of the new autumnal plumage 

 will be seen to be parti-colored, the centre being of a hue different from that of the 

 edge. Let us examine the fall plumage, for instance, of the adult common snow- 

 bunting (Plectrophanes nivalis). The- general color is white, the back, however, 

 spotted with black, and parts of the plumage, especially the head, suffused with 

 brownish ; looking closer at the individual feathers, we find that those on the back are 

 really black, with broad white margins, while the white feathers of the head are tipped 

 with brownish. These edges and borders become very brittle towards the approach 

 of next year's breeding season ; they fall off, leaving the black feather-centres of the 

 back and the pure white part of the other feathers exposed, so that the bird next sum- 

 mer appears white, with black back. It is a similar process which changes the appear- 

 ance of the bobolink (Doliclionyx oryzivorus), besides that of numerous other birds, 

 so radically. 



Changes in color may also take place between the molts and independent of the 

 edge-shedding. In most birds the color of the plumage changes notably towards the 

 end of the breeding season : wing-feathers which formerly were black become light 

 brownish or grayish, vivid colors become dull, and a general fading seems to take 

 place, caused by the wear and tear, rubbing, direct influence of the atmosphere, of 

 rain, and of sunshine, or, as we are accustomed to call it, by abrasion. But the colors 

 may also be intensified, or even radically changed, by abrasion, provided the super- 

 ficial layers which rub off are of such a nature as to conceal or obscure the deeper 

 and differently colored strata. We may mention the common red-poll (Acanthis 

 linarid) as an example. It is but fair to confess, however, that our knowledge of the 

 change of color in the individual feather, after having finished its growth, is still very 

 defective, and that we have to look toward future investigations for answers to many 

 a question. The same remark applies to our knowledge of the pigments in feathers 

 which produce the colors. A coloring matter which is called zoomelanin, and 

 thought to be identical with coriosulphurine, seems to produce all the black and dark 

 hues in birds, w r hile some green colors are due to an admixture of a yellowish pigment 

 called psittacofulvine. A really green pigment has only been found in the touracos, 

 hence the name turacoverdin, and no blue or violet pigment has yet been dis- 

 covered, while red (zooerythrine) is quite common. Another red, turacin, causes 

 the magnificent red on the wings of the Musophagidae. There is no white pigment, 

 but wherever that color occurs it is due to the countless number of interstices between 

 the molecules of the feather, the substance of the latter being colorless. Many tints 

 for example, blue, violet, and certain greens are not due to the pigment, which is 

 black-brown to yellow, but the blue results from a particular surface-structure of the 

 feathers, so that it must disappear if the color-producing parts be destroyed. Thus, if 



