INTllODUCTION. 5 



a few weeks;, as in the eiders (Soinateria), but wo have, on the other liand, examples 

 of the reverse, as in tlie jjtannit,faiis {La(/opus), souie of whicli, at least, show the 

 peculiarity of a jiermanent molt during the whole summer. JIany birds retain the 

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

 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 

 where 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 aulunuial 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 {Plectro2)hanes nivalis). The general color is white, the back, however, 

 spotted with black, and jiarts 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 llie wliite feathers of the head are tipped 

 with brownish. These edges and borders become very brittle towards the aj)])roach 

 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 ajipear- 

 ance of the bobolink {DoUchonyx ori/ziconm), besides that of numerous other birds, 

 so radically. 



Changes in color may also take place l)etween the molts and inde]>endent of the 

 edge-she(lding. In most birds the color of the plumage changes notably towards the 

 en<l of the breeding season : wing-fcatliers 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 ('hanged, by abrasion, ])rovided the super- 

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

 and differently colored strata. We may mention the common red-poll {Acinthis 

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

 change of color in the individual feather, after having fini.shed its growth, is .still very 

 defective, and that we have to U)ok tow;ird future investigations for answei-s to many 

 a (piestion. The same remark aiii>lies 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 coriosuljihurine, seems to ]>roduce all the black and ilark 

 lines in birds, while some green colors ;n-e due to an ailmixlure of a yellowish iii^mcnt 

 called jisittacofulvine. A really green pigment has only been fouml in the touracos, 

 — hence the name tunicoverdin, — 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 ^[uso]iliagida\ There is no while 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 exiunple, blue, violet, and certain greens — are not due to the pigment, whicii is 

 black-brown to yellow, but tin- blue results from a j)articular surl'ace-structure of the 

 feathers, so that it must disajijicar if the color-producing jiarts be destroyed. Thus, if 



