118 METOPIANA PEPOSACA 



Food. Field naturalists have noted that they feed on floating weeds in shallow 

 or shoal water and never on dry land (P. L. Sclater and Hudson, 1889). Small roots, 

 fishes, small insects and snails (Ampullaria) have been found in their crops (D. Rod- 

 riguez, 1918). Daguerre (1920) says he has seen them feeding on floating grains of 

 corn on the inundated fields in winter. The stomach of a male bird collected by Mr. 

 J. L. Peters at Huanuluan, Rio Negro, Argentina, in October and analyzed by the 

 staff of the U. S. Biological Survey, contained 60% animal matter and 40% vegetable. 

 The principal items were ground-up caddis larvae and more than 450 seeds of water 

 milfoil (Myriophyllum) besides seeds of rush and bits of rootstock of grass or sedge. 



Courtship and Nesting. The courtship of this duck is not marked by any 

 bizarre attitudes. The males I have watched threw their heads back quickly at the 

 same time that they uttered their spring call. Dr. Wetmore (MS.), observing them 

 in the field, speaks of four or five males pursuing one female, who remained in the 

 lead. Every now and then one of her suitors rose to flutter along for four or five feet, 

 with the rear portion of the body dragging on the surface of the water. 



The nesting season extends from mid-October to December in the Province of 

 Buenos Aires. In late September a series of thirteen males taken by R. H. Beck 

 (MS.) at Mar del Plata showed enlarged organs, while out of nine females taken at 

 the same time two had the ovaries large and the remainder "swelling." Eggs have 

 been taken on December 9 (E. Gibson, 1920) and some were found in the body of a 

 female as late as January 8 at Barracas al Sud (Hartert and Venturi, 1909). The 

 month of November is the common nesting period. 



For a number of years field collectors (A. H. Holland, 1892; C. H. B. Grant, 1911 ; 

 D. Rodriguez, 1918; E. Gibson, 1920) have reported remarkable parasitic habits in 

 the Rosy-bill. Eggs, supposedly of this species, were found in the nests of many 

 other birds, especially the three coots (Fulica armillata, F. leucopyga, and F. leu- 

 copter a), both swans (Cygnus nigricollis, Coscoroba Candida), the Southern Courlan 

 (Aramus scolopaceus) , the Spot-winged Gull (Larusmaculipennis), Crested Screamer 

 (Chauna chavaria) and even the Maguari Stork (Euxenura maguari). One of these 

 observers (Rodriguez) goes so far as to say that in his opinion the Rosy-bill never 

 builds its own nest. But he admits that these parasitic eggs are seldom hatched and 

 that if they are, the ducklings soon die. The abundance of the species mystifies him, 

 as he confesses. 



Doubts have recently been cast on these observations by Daguerre (1920), sup- 

 ported by Dabbene (1921). The former, after a careful examination feels certain 

 that the ducks' eggs found in the nest of Coots and other birds belong to the 

 Black-headed Duck (Heteronetta atricapilla) and not to the present species. He even 

 believes that the Rosy-bill itself is more or less parasitized by the Black-headed 

 Duck, wherever they are found together. 



