Date of Award

8-1-1981

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

Large numbers of mallards (Anas platyrhynchos) winter in or migrate through middle and northern latitudes of the midcontinent region in North America. Although an intensively studied species, the wintering and staging ecology of mallards north of traditional areas has received limited attention, leaving waterfowl administrators with limited information for developing management guidelines for mallard populations during these periods of the year.

Mallard activity patterns, foraging strategy, and physical condition were studied on the Platte River in south central Nebraska from mid-December to early April, 1978-80. Local movements, time budgets, food habits, physiology, and energetics during winter and early spring provided an improved perspective of mallard requirements during these stages of the annual cycle.

Weather conditions had a major influence on habitat use. Mallard use of the Platte River rose markedly during the mild winter of 1980 and disparity of age and sex ratios was lower than during the previous winter when conditions were more severe. Significant emigration occurred during prolonged periods of cold, which raised questions concerning establishment of traditional wintering grounds and interflyway movements of post-season banded birds. Riverine and canal roost habitats appeared to have similar geophysical characteristics but significantly different microclimates. The warmer canal microclimate attracted mallards during severe weather, but overcrowding, lack of aquatic food, and increased risk of predation caused most mallards to return to riverine habitats when weather conditions improved. The primary activity centers of adults and yearlings were canals and riverine habitats, respectively. Yearlings had lower roost fidelity and made more and longer exploratory flights. Females spent more time feeding than males; males were more alert, aggressive, and spent more time in comfort movements. Paired mallards displaced unpaired birds, suggesting an advantage for being paired during the winter period.

Zea mays, Lemna minor, Polygonum spp., Echinochloa muricata, and Sorghum vulgare were the principal foods consumed during winter and spring migration. Mallards depended heavily on waste corn which formed 97% of the diet in agricultural habitats. The winter diet contained lower levels of nutrients than recommended for captive birds of wild stock, emphasizing the importance of access to aquatic feeding sites. Grazed corn stubble was the preferred agricultural habitat. Mallards lost weight throughout winter but attained prewinter levels during the staging period. Body and carcass weights followed weather trends; females gained weight before males. Gonadal weights remained low until spring. Initiation of female prebasic molt was related to pair status. Energy budgets of paired and unpaired birds were similar, although time budgets were different, suggesting that behavioral patterns optimized energy expenditure for maintenance and productive uses.

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