THE UNDESCRIBED JUVENAL PLUMAGE OF THE 

 YUCATAN JAY. 



Cissilopha yucatanica (Dubois). 



I. 



On September 3, 1911, three jays in immature plumage were 

 received from Yucatan. The plumage was a hitherto unde- 

 scribed one, and a drawing was made of one of the birds on 

 September 8. The subsequent postjuvenal moult transformed 

 the birds into undoubted Cissilopha yucatanica. This change is 

 described in detail in Part II of the present paper. 



Both Sharpe (1) and Salvin and Godman (2) describe the 

 female of this jay as differing from the male in having the beak 

 yellow instead of black and the outer rectrices tipped with white. 

 Our collector who brought north the young birds, reflecting the 

 opinion of the natives in Yucatan, asserts that the white rectrice 

 tips alone characterize the female. Ridgway (4) describes the 

 adult sexes as alike, and considers the yellow beak and white- 

 tipped rectrices as "immature" characters. This he evidently 

 bases on Chapman (3) whose notes on this species are obtained 

 at first hand in the field. Chapman writes as follows : 



"Current descriptions of this bird, including that in the 

 'Biologia,' ascribe the differences shown by certain individuals in 

 the color of the bill and tail to sex, the male being stated to have 

 a black bill and tail, while the female is said to have the bill yel- 

 low and the tail tipped with white. My series of twelve speci- 

 mens show^s that this variation is not sexual, but is evidently due 

 to age. Thus I have males and females with black bills and tails, 

 and also examples of both sexes in which the bill is yellow and 

 the tail tipped with white. The series also contains intermedi- 

 ates between the two extremes. 



1—1877. Sharpe, Cat. Birds Brit. Mus., Ill, 133. 



2—1887. Salvin and Godman, Biol. Cent.-Amer., Aves, I, 498, pi. 35. 



3—1896. Chapman, Bull. Amer. Mus. Nat. His., VIII, 282. 



4—1904. Ridgway, Bull. U. S. Nat. Mus., No., 50, Part III, 315. 



