Two Hawaiian ducks (Anas wyvilliana) at WWT Slimbridge in England. The male has green feathers on his head and is sitting on the right, the female is sitting on the left. The Hawaiian duck is listed as endangered by the IUCN.
A pair of black-headed ducks (Heteronetta atricapilla) at Sylvan Heights Bird Park in Scotland Neck, North Carolina.
The male is darker, while the female is brown.