114 



THE OSPREY. 



quite similar as regards the head plumage, and 

 evidences of active aptosochromatisin were 

 exhiliited in all these cases. One fine old bird 

 from -Mr. Holden's store deserves individual 

 mention. In this particular case, not onl3' 

 were the whole head, throat and neck bright 

 buttercup yellow, but patches of the same 

 color were present upon the breast, back, and 

 rump; even the wings were changing, and 

 yellow was ditfusing itself over the seconda- 

 ries and coverts. As it is stated in Mr. Hol- 

 den's book (Canaries and Cage Birds) that the 

 yellow extends with age, it is probable that 

 this specimen is an old bird. 



The slight difference, if any, in the colora- 

 tion of the two sexes is iiumaterial to the 

 present inquivv. Salvadori states in his vol- 

 ume of the iirilish JIuseum Catalogue, page 

 293, that the female is "like the male." The 

 P.oiles Parrot was selected as the best case 

 to work upon, chiefly because of its readiest 

 accessibility, which facilitated examination. 

 This bird appears perfectly healthy, and is fed 

 for the most part \ipon hemp and sunflower 

 seeds. It represents an average case among 

 those observed at the various stores. 



Before going further into the matter of 

 color change in feathers, it will be well to 

 define a few terms for the purpose of arriving 

 at a more complete understanding. I have 

 used the term "aptosochromatism" in the 

 sense given to it by its coiner, and because of 

 its precise definition and ready comprehension. 

 Just as the simple term "moult" has often 

 been misused or abused, in its meaning or ap- 

 plication to a class of cases in which it is 

 not concerned and to which it, therefore, does 

 not apply, so has "dichromatism" sometimes 

 been misunderstood or misapplied. Properly 

 speaking, dichromatistn means double colora- 

 tion, or any two different colorations which 

 a bird may exhibit under different conditions 

 of age, sex, season, etc. Albinism, melanism, 

 erythrism, and the like, are examples of more 

 or" less abnormal dichromatism which may 

 permanently affect certain individuals of a 

 species; a Heron, which is white when young 

 and colored when adult, is an example of nor- 

 mal dichromatism dependent upon age of the 

 individual. Again, the tenn dichromatism 

 may be and has been used in connection with 

 total or very extensive color changes, which 

 regularly result from moult, and also in con- 

 nection with similar changes which occur in- 

 dependently of moult: in the latter case, the 

 term is synonymous with aptosochromatism. 

 The Bobolink, as demonstrated by Dr. A. P. 

 Chadliourne (Auk, xiv, Apr., 1S97, pp. 137-149, 

 plate), may have a spring moult, and also a 

 further color change, resulting from loss of 

 the barbs of feathers without any further loss 

 of feathers. Thus dichromatism may lie used 

 in a broad generic sense, to be specified or 

 qualified by modifying terms; as. for example, 

 dichromatism or change of color due to moult, 

 consequent upon loss of old feathers of one 

 color and gain of new feathers of some other 

 color. This may be called ptosochromatism, 

 in distinction from that color change which 

 occurs in feathers themselves, without moult, 

 and which constitutes aptosochromatism. 

 The latter term may be briefly defined as 



color change of the individual without loiss or 



gain of plumage. ^Vhen change from one par- 

 ticular color to another without moult is to 

 be specified, it may be easily indicated. Thus, 

 chlorochrys-aptosochromatism means change 

 of color from green to j'ellow without loss of 

 plumage: that is, without loss of feathers 

 enough to constitute a moult. The applica- 

 tion of this last term, "moult," is usefully re- 

 stricted by Dr. Chadbourne, on page 146 of his 

 article on the "Spring I'luinage of the Bobo- 

 link," and it will be used with such restriction 

 in this article. The xanthochroism of Ciadow 

 (Newton's Diet., Article Color, p. 99), is in- 

 ai)plicable to the present case, in view of his 

 suggestion that the process may be one of 

 "arrested development;" for, as I shall show, 

 the color change occurs in Chrysotis levail- 

 lanti after the feather which turns from 

 green to yellow is perfected. 



The general exteraal appearance of the 

 chlorochrysotic change will be first consid- 

 ered. Macroscopically, the contour feathers 

 of the crow-n consist of main shaft and after- 

 shaft, both with the lateral appendages or 

 barbsconstituting the vanes, which are downy 

 in the aftershaft, and need not be further no- 

 ticed in the present connection. The normal 

 green feather is represented in Fig. 1 of the 

 plate. tlradually, as activity increases in the 

 individual feather, a faint trace of color 

 change from green to yellow becomes appar- 

 ent, as represented in Fig. 2. This stage va- 

 ries much, the yellow extending well down 

 one side of the vane in some cases, while in 

 others it only margins one edge of one vane 

 at the end, and in others again it tips the ends 

 of both vanes. The change thus begun pro- 

 gresses, and continues till an intermediate 

 stage is reached, as shown in Pig. 3, where the 

 feather is green-centered, but widely mar- 

 gined on both sides with yellow. Feathers in 

 this stage are conspicuous in the plumage, and 

 offer oljvious proof of aptosochromatism. The 

 yellow increases in extent till the green is 

 almost g-one. as represented in Fig. 4. The 

 change of color goes on till the metachrosis 

 is completed, as shown in Fig. 5, in which the 

 last traces of green have disappeared, and the 

 individual feather that was once green in all 

 its colored portions has become entirely yel- 

 low in those same portions. During this total 

 change the irregtilaritj' of the substitution of 

 vcllow for g-reen on particular barbs is not 

 a little curious and interesting. It should be 

 borne in mind that each barb is itself like a 

 tiny feather, of which the barbules. with their 

 barbicels and hooklets, represent vanes; and 

 any barb may become the seat of a color 

 change independently of other barbs, just as 

 a whole feather may change color independ- 

 ently of other feathers. The five stages se- 

 lected for illustration could readily be taken 

 from various parts of the plumage of the 

 head: and in view of this fact it seems sur- 

 prising that the matter should not have hith- 

 erto attracted much attention. Even the 

 dealers appeared to be ignorant of the true 

 state of the case. The change, however, is 

 very slow and gradual. In an interval of ten 

 days I could detect but slight increase of yel- 

 low in certain feathers, and, as already re- 

 marked, two months were required to advance 



