192 o J Brooks, Notes on American Ducks. d59 



5. Nail of bill. Ridgway gives width in americana female 

 "not more than .20." I have a female with a nail width of .22. 

 In islandica female "not less than .23," this holds good even 

 when a very young islandica is included, it has a nail .26 wide. 

 Brewster says he is unable to verify this distinction with his 

 series, so it must be reckoned uncertain. 



Nail larger and more hooked at tip ('Game birds of Cali- 

 fornia'), also Munro in 'The Condor,' No. 1, Vol. XV. "Nail is 

 wider at the front, projects further over tip of bill, and is slightly 

 raised above the bill forming a noticeable lump." 



All of these distinctions hold good but then again, as given, 

 they are mostly comparative. 



6. Color of bill. The yellow color of the bill in islandica is an 

 oft-quoted distinction and one to which Mr. Brewster attached 

 great faith. 



The following facts I can vouch for: Adult females of americana 

 usually have a yellow or dull orange bar on the terminal third 

 of the upper mandible, sometimes more than one-third of the 

 bill is yellow and in one instance (and here I speak from memory 

 only) the entire bill orange yellow. 



The young of this species have always (?) an olive bill — no 

 yellow. 



The young females of islandica have an olive, brownish, or 

 blackish bill, no yellow. In the adult females it is wholly orange 

 or cheese-colored, or else the same with the base more or less 

 flecked with dusky. But this is a seasonal feature only. During 

 the past summer (1919) I kept a number of breeding females 

 under observation. When pairing with the males in the latter 

 part of April and early in May, all had orange bills, even some 

 of the unmated immatures of the previous year had the bill more 

 or less orange. In July, when these same females were each 

 leading a brood on their respective ponds, all had dusky or black- 

 ish bills, showing no yellow at all. 



So the yellow bill, which can only apply to adult females at 

 best, cannot be relied on at all seasons. 



7. Skull. The difference in the shape of the frontal bones has 

 been noticed by several authorities, it is pronounced enough in 

 adult males, but a rather subtle distinction when applied to young 

 birds (see figures p. 362). 



