1914] Beebe: Postponed Moult in Passerine Birds. 257 



the moult was from nuptial to nuptial, not from nuptial to win- 

 ter plumage. The dull colors of the winter season had been 

 completely suppressed. 



We thus have proof that the outward manifestation of the 

 sequence of plumage in these birds is not in any way predestined 

 through inheritance bringing about an unchangeable succession, 

 in the case of the tanager, of scarlet-green, scarlet-green, year 

 after year. The katabolic changes of pigmentation in the blood 

 are induced by certain seasonal factors, whether internal, as the 

 sexual organs, or external, as food or changing meteorological 

 conditions, we know not. But we do know that this orderly 

 succession may be interrupted by certain external conditions in 

 the environmental complex. 



The pigmental changes in the blood which induce the green 

 autumn garb, undoubtedly went on as usual in my birds. The 

 one individual which reacted to the change in temperature 

 proved this. But in course of time, although this pigment was 

 not permitted to be expended in its normal feather-impregna- 

 tion, it was changed by some seasonal alchemy, and the scarlet 

 pigment made ready. When at last I permitted the moult to 

 take place, the bird was clothed in the dress appropriate to 

 the season, and if wild, would have suffered no handicap in the 

 functions for which its brilliance is intended. It is interesting 

 to note that the green plumage which was so completely sup- 

 pressed, is unquestionably the more ancestral and primitive, as 

 it is the garb of the young of both sexes and of the adult female. 



Nature offers us a curious comparison and normal control 

 in the Summer Tanager, Piranga rubra (Linnseus) , the male of 

 which retains the scarlet plumage throughout the year. So that 

 what I was able to induce by abnormal methods, is the normal 

 sequence in this closely, indeed generically, related species. 



Until I have further and more complete data, checked by 

 results derived from control of other factors of the environment, 

 I shall refrain from further comment on the significance of 

 this initial experiment. 



There is genuine satisfaction in thus making even the 

 merest beginning at the elucidation of these problems, which in 



