Volume 1. Number lU. 



EFFECT OF A POSTPONED MOULT UPON 



THE SEQUENCE OF PLUMAGE IN 



CERTAIN PASSERINE BIRDS 



By C. William Beebe, Curator of Birds. 



In 1908 I published in the American Naturalist an account 

 of certain experiments on this subject, and since that time I 

 have had so many requests for excerpts that I have thought it 

 advisable to record the experiments again in full in Zoologica. 

 As this work is to be renewed and elaborated in the future, easy- 

 reference to this preliminary paper is desirable. 



One of the best-known phases of bird moult is at the com- 

 mencement of the season of courtship, when the male of many 

 species assumes a more or less brilliant or specialized plumage 

 and in the auturnn sheds it in exchange for a more sombre win- 

 ter garb, often resembling that of the female. In the United 

 States, striking examples are the Scarlet Tanager, Piranga ery- 

 thromelas Vieillot, and the Bobolink, Dolichonyx oryzivorus 

 (Linnaeus). In Africa, weaver birds of the genera Vidua and 

 Pyromelana, exhibit radical seasonal changes. 



The problem which attracted me was the discovery of the 

 factors which determine this seasonal change. So untouched 

 is this field of research that at first no definite method of- 

 fered itself; there was no previous line of work to be followed 

 or extended. The most hopeful way of work seemed to be to 

 clear the ground by gradually eliminating all negative fac- 

 tors, to demonstrate those conditions which would inhibit such 

 a plumage change, and thus narrow down to the important dy- 

 namic phenomena of physiology or external environment. The 

 thousand and one influences which impinge upon the organism 

 from its environment (using that word in its widest sense), 

 may be grouped under certain heads, all or any of which may 

 be concerned in moult and in sexual plumage, change of color 



