152 BIRDS OF LA PLATA 
large number of birds appea#to pair for life, as they 
are usually seen in pairs at all seasons of the year. 
In the autumn and winter months I have sometimes 
observed small flocks composed of males only, but 
these were perhaps young birds not yet paired. They 
feed in shallow water, where by plunging the head 
down they can reach the mud at the bottom; and 
when several are seen thus engaged, all with their 
heads and necks immersed, they look curiously like 
headless ducks floating on the water. When dis- 
turbed or flying the male emits a low sputtering 
sound, and this is its only language. They are 
resident, and the least wary of ducks; never engage, 
like other species, in real or mock combats; and 
their flight is rapid and violent, the wings beating 
quickly. 
ROSY-BILLED DUCK 
Metopiana peposaca 
Above black, back of head and neck glossed with purple, back 
finely striated with white ; speculum white ; primaries greyish white ; 
belly minutely vermiculated with white and grey; bill rosy red, 
enlarged at the base, feet yellow; length 19, wing 9.4 inches. Female: 
above brown, bend of wing, speculum, and belly white; bill and feet 
dull blue. 
THE Rosy-billed Duck, usually called ‘‘ Black Duck ” 
in the Plata, inhabits the Argentine country from 
Paraguay to Patagonia, and also occurs in Uruguay 
and Chili, but does not extend to Brazil. 
