96 HETERONETTA ATRICAPILLA 



Estancia Los Yngleses, Province of Buenos Aires. "They frequented pools sur- 

 rounded by rushes, where the water was from two to three feet deep, and were shy 

 and retiring, so that it was difficult to observe them. On my first encounter I found 

 two pairs on a small pond with Coots, and other ducks. To my astonishment the 

 Black-headed Ducks dove when startled and disappeared like so many grebes, 

 evidently seeking the shelter of the rushes. Another pair was observed on Novem- 

 ber 9, 1920, when I was fortunate enough to secure the male, though both birds dove 

 instantly at the flash of the gun. The female disappeared and was not seen again. 

 When in the water the birds suggest Ruddy Ducks (Oxyara jamaicensis) , though the 

 tails are not held at an angle as in the ducks of that genus. 



"Black-headed Ducks were evidently breeding during the first week in November. 

 The females noted swam about with their heads erect, behaving like other ducks. 

 Males followed them or faced them with necks drawn in and throats puffed out, at 

 intervals raising the point of their bills and giving a low note, quah-quah, barely 

 audible at forty-five yards. It is possible that in diving quickly the birds use wings 

 as well as feet, but on this point I am not certain." 



It is very extraordinary that no nest of this species has ever been found, or at any 

 rate described. This gap in our knowledge of the bird's life-history may be due to 

 the fact that the species is extraordinarily parasitic, depositing its eggs in the nests 

 of such birds as the Coscoroba Swan (Coscoroba), the Crested Screamer (Chauna), 

 the South American Limpkin (Aramus), Gulls (Larus), Coots (Fulica), White-faced 

 Ibises (Plegadis), Black Rails {Pardir alius), and even the nests of the Chimango, 

 or Southern Caracara Hawk (Milvago chimango). Ducks' eggs found in such situa- 

 tions were at first attributed to the Rosy-billed Duck (D. Rodriguez, 1918), but a 

 later writer (Daguerre, 1920) has discovered that these parasitic eggs are slightly 

 different from those of the Rosy-bill, being more whitish and the surface very finely 

 granulated ; they are also thicker and more blunt. Most convincing is his statement 

 that these supposed Rosy-bill eggs are identical with a mature egg which was taken 

 from the oviduct of a female of the Black-headed Duck. It may be remarked in this 

 connection that the Black-headed Ducks are not uncommonly seen in the company 

 of Coots (E. Gibson, 1920; Wetmore, MS.). 



Because of the scarcity of information about the nesting of this duck, I think it is 

 worth while to quote a tale that was related to Lord William Percy in Santiago, in 

 1923. A monk (Flaminio Ruiz) in charge of the museum there said that when he 

 was in Cautin Province in December he saw from his boat in the marshes a duck 

 come from a hole in the fork of a tree forty feet from the ground. It was, he thought, 

 a Black-headed Duck, and the young birds from the nest came tumbling out one 

 after another on to the water beside the old bird below. 



This duck has never been imported alive into North America or Europe, and no 

 hybrids have ever been described. 



