Food availability and feeding preferences of breeding fulvous whistling-ducks in Louisiana ricefields

Expansion of the breeding distribution of the Fulvous whistling-duck (Dendrocygna bicolor) into the southeastern United States after the mid-1800s coincided with the establishment of rice (Oryza sativa) cultures in Texas, Louisiana, and Florida. In southern Louisiana, where approximately 80% of rice is aerially seeded in water, Fulvous whistling-ducks are suspected of feeding extensively on planted rice and are considered a nuisance. To determine the extent of rice utilization by ducks nesting in southwestern Louisiana, we estimated food availability in ricefields and assessed feeding preferences. We also examined effects of sex and stage of reproduction on food selection. Feeding sites in Louisiana ricefields that were tilled and flooded in preparation for spring planting, contained abundant foods (mean ± SE = 109.0 ± 18.0 g/m2, especially seeds of moist soil plants such as signalgrass (Brachiaria extensa), beakrush (Rhynchospora sp.), and flatsedge (Cyperus iria). Diets of males and females were similar (P = 0.080), but varied through the reproductive cycle (P = 0.008). Consumption of plant material was slightly reduced during the period of rapid ovarian follicle growth in females; however, ingestion of animal foods never exceeded 4%. Fulvous whistling-ducks exhibited feeding preferences (P < 0.001) with aquatic earthworms (Oligochaeta) and wild millet seeds (Echinochloa sp.) being preferred over other food taxa. Rice made up <4% of the diet and was selected in proportion to its availability before and during period of rapid follicle development. Almost 25% of the diet of incubating females consisted of rice; however, we concluded that crop depredation by Fulvous whistling-ducks (≤0.1%) was of minor importance relative to other potential sources of crop loss. Indeed, use of ricefields by whistling-ducks may actually benefit farmers if ingestion of seeds of undesirable plants reduces the need for costly herbicide treatments.