116 METOPIANA PEPOSACA 



in Buenos Aires Province on May 8, 1920, 1 was told that for the last few months there had been very 

 few ducks on account of the low water, the result of a protracted dry period. During the night of 

 May 9, however, rain began to fall and continued for twenty-four hours, during which time over five 

 inches fell. At about 3:30 on the afternoon of the 11th a flight of ducks appeared coming from the 

 northwest (afterward thought to be nearly 75% Metopianas). It was not a steady flight, rather a 

 succession of roughly V-shaped flocks of from thirty or forty up to one hundred or so individuals, 

 sometimes passing two or three per minute, followed by an interval of five or ten minutes in which no 

 flocks passed. This flight continued until dark and was still going by up to half-past nine the next 

 morning. After this there were scattering flocks for a day or two." Most of these ducks appeared to 

 be males. At the same time many Brown Pintails were flying and these also were all or nearly all 

 male birds. 



When he was collecting at Huanuluan, Rio Negro Province, Mr. Peters first noted Rosy-bills on 

 September 13. 



GENERAL HABITS 



The Rosy-billed Duck may be thought of as distinct from the Pochards and Scaups, 

 yet as having something in common with this group and perhaps also with the Red- 

 crested Pochard. Its chief external peculiarity is the gorgeously colored and much 

 swollen bill in the males. The trachea in this sex is supplied with a huge expanded 

 chamber in its central portion, a character common also to the Velvet Scoter 

 (CEdemia fusca) and in a lesser extent to the Harlequin Duck (Histrionicus). 



This duck seems to prefer shoal water or pools in the marshes rather than the 

 deeper water in which many of our more typical diving ducks feed. In this respect 

 it resembles the Red-crested Pochard, only it is a more extreme case. 



In the field the bill of the male makes a distinctive mark. In mixed collections of 

 water-fowl females both on the wing and in the water resemble closely the females of 

 Red-heads or Pochards, but the white under tail-coverts are easily distinguished. 

 Mr. J. L. Peters writes me that the male is always easy to tell from any other duck. 

 When at rest the glossy-black plumage and crimson swollen bill are sufficient, and 

 when flying the same characters coupled with the white-tipped secondaries and 

 white inner webs to the primaries as well as the large size make a mistake almost 

 impossible. He describes the female as looking a good deal like a female Canvas-back. 



Wariness. Wetmore (MS.) found that in Buenos Aires Province these birds 

 showed "entire lack of fear of any object not wholly visible to them, so that to secure 

 a shot it was often only necessary to crouch in the grass or rushes when the birds 

 were circling on the wing." Nevertheless the Rosy-bill may be classed as a moder- 

 ately wary bird, though like other diving ducks scarcely to be compared with the 

 Widgeon or the Pintail. 



Gait, Swimming, Diving. The gait is less awkward than that, for example, of 

 the Scaups. Certainly a great deal of their food is obtained in shallow water or from 

 floating vegetation and some collectors have never seen them dive; while in cap- 



