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Dennis W. Woolington

Publications and source records attributed to Dennis W. Woolington.

5 recordsLinked to original sources
USGS1993

Sex ratios of canvasbacks wintering in Louisiana

Disparate sex ratios in waterfowl are considered indicative of differential survival between the sexes and may limit reproductive potential. Because other studies have shown canvasbacks (Aythya valisineria) have highly skewed sex ratios, I examined aerial photographs from surveys flown monthly during winters 1987-88 and 1988-89 to determine sex ratios of canvasbacks in Louisiana where the wintering population is increasing. Estimated statewide sex ratios (proportion male) were balanced during the initial arrival period in November (1987: 0.505, 1988: 0.524), dominated by males during December-February (range = 0.600- 0.655), and then dominated by females as birds departed in March (1989: 0.419). Sex ratios varied geograph- ically with males being more prevalent in flocks at inland sites than in coastal areas. Canvasback sex ratios did not vary by flock size nor between major- and minor-use areas. Canvasback sex ratios in Louisiana appeared to be representative of the population wintering in the lower Mississippi Valley and Gulf Coast region and were less male dominated than the sex ratios projected for the population wintering in the Atlantic Flyway. Overall sex ratio characteristics imply that female canvasbacks in Louisiana may have higher annual survival or recruitment rates relative to males than occur in other wintering populations. I suggest that this may partially explain the observed increases in canvasbacks wintering in Louisiana.

Louisiana↗
USGS1990

Food habits of wintering canvasbacks in Louisiana

We studied the food habits of canvasbacks ( Aythya valisineria ) at Catahoula Lake (inland) and the Mississippi River Delta (coastal), Louisiana, from November 1987 to February 1988. Plant foods comprised >97 aggregate percent dry mass of the canvasback diet. The proportion of plant material eaten did not vary with sex, age, or month, or differ between study sites or nocturnal and diurnal collections. Tubers of chufa flatsedge ( Cyperus esculentus ) and common arrowhead ( Sagittaria latifolia ) made up 94% of the canvasback diet at Catahoula Lake. Common and grassy arrowhead ( Sagittaria graminea ) tubers and American bulrush ( Scirpus americanus ) rhizomes and seeds formed 94% of the canvasback diet at the Mississippi River Delta. Consumption of specific food taxa did not vary with sex, age, or month at either study site. Canvasbacks at the Mississippi River Delta preferred seeds of American bulrush over all other foods, but American bulrush rhizomes were underrepresented in the diet. Densities of subterranean plant foods at Catahoula Lake and the Mississippi River Delta are apparently higher than at other major canvasback concentration areas and enable canvasbacks wintering in Louisiana to improve their physical condition before spring migration.

Louisiana↗
USGS1990

Influence of ingested lead on body mass of wintering canvasbacks

We determined the prevalence of lead shotgun pellets in gizzards of canvasbacks ( Aythya valisineria ) collected at Catahoula Lake and the Mississippi River Delta, Louisiana, during winter 1987-88 to assess the influence of ingested lead shot on canvasback body mass. The prevalence of ingested lead shot was significantly higher at Catahoula Lake (27%) than at the Mississippi River Delta (4%). Canvasbacks collected at Catahoula Lake showed significant differences in prevalence of ingested lead shot by age and month. We attributed age-related and seasonal variations to differences in foraging effort and exposure time. Body mass of canvasbacks at Catahoula Lake, after accounting for age, monthly variation, and body size, was significantly reduced (120 g or 10%) in birds that had lead shot in their gizzards.

Louisiana↗
USGS1989

Trends in wintering canvasback populations at Catahoula Lake, Louisiana

Aerial survey data (1968-1989) and water gauge readings (1958-1989) were examined to detennine trends in and relationships between canvasback (Aythya valisineria) populations and water levels at Catahoula Lake, Louisiana. Wintering canvasback populations at Catahoula Lake have increased over the past 21 years. A peak population estimate of 78,000 canvasbacks was recorded in January 1988. There was a significant relationship between increases in wintering canvasback numbers and increased November water levels. No significant changes in December or January water levels nor relationships between wintering canvasback numbers and December or January water levels could be detected. In recent years, Catahou1a Lake has become one of the most important canvasback wintering areas in North America. We conclude that the increased availability of open water feeding habitat has been a major factor in the increased usage of Catahoula Lake by canvasbacks.

Louisiana↗