 The fulvous whistling duck feeds in wetlands by day or night , often in mixed flocks with relatives such as white @-@ faced or black @-@ bellied whistling ducks . Its food is generally plant material , including seeds , bulbs , grasses and stems , but females may include animal items such as aquatic worms , molluscs and insects as they prepare for egg @-@ laying , which may then comprise up to 4 % of their diet . Ducklings may also eat a few insects . Foraging is by picking plant items while walking or swimming , by upending , or occasionally by diving to a depth of up to 1 m ( 3 @.@ 3 ft ) . Favoured plants include water snowflake , aquatic ragweeds , bourgou millet , shama grass , Cape blue water lily , waxy @-@ leaf nightshade , beakrush , flatsedge and polygonums . Rice is normally a small part of the diet , and a survey in Cuban rice fields found that the plants taken were mainly weeds growing with the crop . However , in a study in Louisiana , 25 % of the diet of incubating females consisted of the cereal . 
