 This species is usually found in small groups , although substantial flocks can form at favoured sites . It walks well , without waddling , and although it normally feeds by upending , it can dive if necessary . It does not often perch in trees , unlike other whistling ducks . It flies at low altitude with slow wingbeats and trailing feet , in loose flocks rather than tight formation . It feeds during the day and at night in fairly large flocks , often with other whistling duck species , but rests or sleeps in smaller groups in the middle of the day . They are noisy and display their aggression towards other individuals by throwing back their heads . Before taking off in alarm , they often shake their head sideways . 
