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) culture s in Texas, Louisiana, and Florida. In southern Louisiana, where appro ximately 80% of rice is aerially seeded in water Fulvous whistling duc ks are suspected of feeding extensively on planted rice and are consid ered a nuisance. To determine the extent of rice utilization by ducks nesting in southwestern Louisiana, we estimated food availability in r icefields and assessed feeding preferences. We also examined effects o f sex and stage of reproduction on food selection. Feeding sites in Lo uisiana ricefields that were tilled and hooded in preparation for spri ng planting, contained abundant foods (mean +/- SE = 109.0 +/- 18.0 g/ m(2)), especially seeds of moist soil plants such as signalgrass (Brac hiaria extensa), beakrush (Rhynchospora sp.), and flatsedge (Cyperus i ria). Diets of males and females were similar (P = 0.080), but varied through the reproductive cycle (P = 0.008). Consumption of plant mater ial was slightly reduced during the period of rapid ovarian follicle g rowth in females; however, ingestion of animal foods never exceeded 4% . Fulvous whistling-ducks exhibited feeding preferences (P < 0.001) wi th aquatic earthworms (Oligochaeta) and wild millet seeds (Echinochloa sp.) being preferred over other food taxa. Rice made up <4% of the di et and was selected in proportion to its availability before and durin g period of rapid follicle development. Almost 25% of the diet of incu bating females consisted of rice; however, we concluded that crop depr edation by Fulvous whistling-ducks (less than or equal to 0.1%) was of minor importance relative to other potential sources of crop loss. In deed, use of ricefields by whistling-ducks may actually benefit farmer s if ingestion of seeds of undesirable plants reduces the need for cos tly herbicide treatments.