USGS · 70210082
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Don Fankhauser. 1962. Observations of birds feeding on overwintering corn borer. https://pubs.usgs.gov/publication/70210082
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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.
We determined diurnal time-activity budgets of Canvasbacks ( Aythya valisineria ) at Catahoula Lake and at the Mississippi River Delta, Louisiana, from December 1987 to March 1988. Canvasback feeding, resting, locomotory, and comfort activities varied by month and location with a month-location interaction. Moreover, the percentage of time spent feeding varied by sex with a month-sex interaction. Study site differences in the time- activity budgets of wintering Canvasbacks may be related to characteristics of their foods, foraging mode, disturbance level, and physical features of habitats at the two study sites. Canvasbacks wintering in Louisiana generally spent less time feeding and more time resting during the day than they did in Mississippi or coastal South Carolina. Levels of agonistic behavior were lower than those observed in South Carolina. We found no evidence of male dominance of female Canvasbacks in Louisiana.
Six male Red-winged Blackbirds scattered throughout 2 marshes were vasectomized in 1971, and their females began laying infertile clutches in 5 days. However, of 39 clutches on their territories, 27 (69%) were fertile. In 1972, 30, 50, and 100% of the males in 3 small isolated marshes were vasectomized, and 44, 33, and 12% of the clutches on their territories were fertile, respectively. All clutches were fertile in a fourth marsh where /// all males were sham-operated. All clutches checked were fertile on territories of fertile males adjacent to sterilized males. During the 2 years there were only 4 partially fertile clutches, 2 each on vasectomized and fertile males' territories. Examination of reproductive tracts of female Red-wings from other marshes showed that sperm retained from copulation were abundant during nest-building or egg-laying but had dropped to a few by hatching. In vasectomy studies, vasectomized males whose territories were the farthest from fertile males had the lowest percentage of fertile clutches. This and other evidence indicated that fertile clutches on territories of vasectomized males may have been due to females being promiscuous with fertile males. The occurrence of fertile clutches on territories of vasectomized males indicates that sterilizing some of the males in a population (as in a chemosterilant program) would not result in a proportional decrease in fertile clutches. However, the decreases achieved (up to 88%), and the probability of better results in an actual program, indicate that male chemosterilization would be a feasible means of reducing Red-wing populations.