PRELIMINARY REPORT ON AN INVESTIGATION 

 OF THE SEASONAL CHANGES OF 

 COLOR IN BIRDS 



C. WILLIAM BEEBE 

 New York Zoological Park 



It is a well-known fact that the males of many species 

 of birds assume a special nuptial plumage at the begin- 

 ning of the breeding season, sometimes radically different 

 from the plumage of the winter. Especially marked 

 examples are scarlet tanagers (Piranga erythromelas), 

 bobolinks (Dolichonyx oryzivorus), and certain weaver 

 birds of the genera Vidua and Pyromelana. 



We know that the native birds mentioned above lose 

 their brilliant breeding plumage in the early fall and 

 assume a winter dress approximating that of the female. 

 When we consider such a case as the scarlet tanager and 

 the summer tanager {Piranga rubra rubra), the former 

 changing annually from scarlet to green, the latter re- 

 maining scarlet at all seasons, we have an interesting 

 difference in two closely related species giving definite 

 data from which to work. The problem which I have set 

 myself, and at the solution of which I have made but the 

 merest beginning, is, What is the cause of, or what factors 

 determine, this seasonal change in the males of the 

 scarlet tanager and the bobolink? 



So unbroken is the field of research in all such prob- 

 lems as this that the most hopeful way of working is to 

 clear the ground by gradually eliminating all negative 

 factors, and thus narrowing down to the important dy- 

 namic qualities of the environment. 



On hastily reviewing the field, the following factors 

 have occurred to me as being the most important in bring- 

 ing about, either directly ontogenetically, or indirectly 

 phylogenetically, seasonal change of color: 

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