Flock of Plumed whistling ducks, Australia. Flock of Plumed Whistling Ducks / Tree Ducks (Dendrocygna eytoni) - whistle and posture in group communication at sunset beside a Gulf lowland billabong, their daytime roost, in the Gilbert-Smithburne River Delta, Gulf of Carpentaria, Queensland, Australia, before flying off at dusk to their night time feeding areas on the moist fringes of drying floodplain wetlands.