Vol. XXIX1 



1912 ] Phillips, The American Black Ducks. 305 



Anas aberti — Abert's Duck. 



This duck, represented by the single type specimen, taken at 

 Mazatlan on the west coast of Mexico, was described by Mr. 

 Ridgway in 1878 (Proc. U. S. Nat. Mus., Vol. I, p. 250). 



At that time A. wyviUiana had just been described by Mr. Sclater 

 from a male specimen, and the sex dimorphism of that species was 

 not recognized. Mr. Ridgway compared his A. aberti (Type No. 

 12789 U. S. Nat. Mus.) with a specimen of A. wyviUiana thought 

 to be a female. It appears, however from his description (p. 251) 

 that this bird must have been a male (V-shaped breast markings, 

 densely streaked throat, etc.) so that the similarity of A. aberti 

 and A. wyviUiana escaped his notice. 



In 1888 Dr. Stejneger (Proc. U. S. Nat. Mus., Vol. II, p. 99) took 

 up the question of A . aberti. He says : " So close is the similarity 

 that I am unable to distinguish No. 113450 (A. wyviUiana), from 

 the type of A. aberti except by the larger size and the total absence 

 even of an indication of supraocular or transocular stripes." Now 

 a comparison of the size of A. aberti with four other undoubted 

 female specimens shows that it is in one case even larger than A. 

 wyviUiana. As to the stripes on the head, I can see no difference 

 in comparing the two specimens above referred to by Dr. Stejneger 

 and at best the supraocular and transocular stripes in the Hawaiian 

 ducks are very indefinite. They are barely perceptible in the 

 female and absent in the male. 



A careful comparison of the type of A. aberti with the four other 

 undoubted female specimens in this museum and the National 

 Museum shows no essential difference in color, pattern or size, 

 hence it appears that in the absence of any further material from 

 Mexico A. aberti must be considered as a female Hawaiian duck, 

 accidentally occurring in Mexico and no longer deserving a specific 

 name. These facts are now probably perfectly familiar to Mr. 

 Ridgway so that the above remarks are not to be taken at all in 

 a critical sense. 



