220 U.S. NATIONAL MUSEUM BULLETIN 237 past i 



In spring the bill color changes gradually from the winter "horn- 

 color" (but sometimes "ecru-olive" with "citron yellow" at gape, 

 or bright "wax yellow" or pale pink) to hght green or pea green in 

 late spring, and in June to light bluish green. It is possible to tell 

 summer birds in collections by the bluish green color of the bills. 



G. Hapgood Parks, who has banded more than 5,000 evening 

 grosbeaks in Connecticut, wrote to Mr. Bent in 1947: "During the 

 winter we made a study of the color of the birds' bills and learned 

 that by late February (Feb. 28) the biUs began to show signs of peeling 

 from the tip and edges. An apparent loosening of the surface mem- 

 branes gave the upper mandibles of some of the birds a whitish and 

 swollen appearance across the base of the bill near the feathers. 

 This latter condition became more apparent on more birds during 

 the first week of March." In 1951 he added the following: "The 

 actual color change of the bill is apparently due to pigmentation. 

 The mottled stage, in which many bills are seen, bears evidence of 

 this fact. Bills showing no peeling at all are not infrequently partly 

 green with areas which retain the 'bone' color typical of the bills in 

 winter. The peeling off of a colorless surface layer apparently helps 

 to promote the 'new' polished appearance of the bill. 



"The peeling is much more conspicuous on the upper mandible, 

 although some peeling of the lower mandible also occurs. I find 

 that my notes about the bills say, most frequently, 'bill green and 

 peeling.' About as often the entry is, 'blue-green lower, peeling 

 upper,' or, 'mottled lower, peeling upper.' I feel certain that the 

 entire surface of the upper mandible peels, I am not at all sure that 

 the same condition holds for the lower mandible. I would not dare 

 to say that the bills of all of the birds peel, although I feel very strongly 

 that such is the case." 



The adult winter plumage is produced by a complete postnuptial 

 molt. The earliest date for the beginning of the molt I have noted 

 is June 28, when a female (one of a nesting pair at the Ivor Bird 

 Observatory) molted a first primary and the male molted the first 

 primary of both wings. On August 25 the male's new tail was half 

 grown. L. H. Walldnshaw (1936) tells of a captive bird that started 

 to molt on July 16 and did not finish until after November 1. 



M. J. Magee (1926b) writes: 



* * * After molting, the feathers in the white wing patches of both males 

 and females are distinctly edged with yellow. All of the descriptions of the 

 plumage that I have seen, from Andubon down, are very much as given by 

 Professor Barrows in "Michigan Bird Life," in which for the male it is said, 

 "most of the secondaries and their coverts snowy white;" and of the female, 

 "primaries and secondaries black, boldly spotted with white." This limited 

 description may be due to the fact that only specimens taken in spring were 



