Feeding Ecology of Breeding Blue-Winged Teals

Abstract

A 5-year investigation of factors influencing the selection of foods consumed by blue-winged teals (Anas discors) during the breeding season in the glaciated prairie region of south-central North Dakota showed that birds first arriving on the breeding grounds consumed a diet consisting of 45 percent invertebrates. The proportion of animal foods in the diet increased to 95 percent at the onset of the nesting season. The quality and quantity of foods selected at any given time were influenced by the biological demands and morphological adaptations of the bird, the behavior and ecology of the invertebrates selected as foods, and the general nature of the aquatic ecosystems as determined by the hydrology and geology of the area and modified by land use and weather. Feeding activities changed significantly when food availability within the aquatic ecosystem changed. During the spring and early summer, temporary and seasonal wetlands, if not severely disturbed, were of paramount importance to breeding blue-winged teals since they provided abundant and readily available, high protein, animal foods. Later in the summer when seasonal wetlands began to dry up, insects began to emerge in the semipermanent ponds and lakes, and feeding intensity shifted to these more permanent waters. This trend, however, was often reversed temporarily during the early summer following heavy precipitation that refilled shallow water areas and again stimulated invertebrate development. J. WILDL. MANAGE. 38(3):396-407 Information concerning foods consumed by blue-winged teals during the breeding season is scarce. Early studies concentrated primarily on fall and winter collections (Mabbott 1920, Bennett 1938, Martin and Uhler 1939, Kortright 1943). The data presented here describe the foods selected by breeding blue-winged teals over a 5year period (1967-71) and are part of a larger study designed to provide information to assess the significance of changes occurring in waterfowl breeding habitat on the prairies. The blue-winged teal is the most abundant breeding duck in North Dakota; the statewide population in 1967 was estimated to contain 680,000 breeding pairs (Stewart and Kantrud 1972a). The various aspects of the life history of the blue-winged teal have been described by Bent (1923), Bennett (1938), Kortright (1943), Delacour (1956), and Johnsgard (1965). The first birds generally arrive in south-central North Dakota during April and nesting is usually initiated by mid-May. Attempts by unsuccessful females to renest are generally terminated in early July. Appreciation is extended to J. C. Bartonek for encouragement and sincere interest; and to V. A. Adomaitis and J. A. Shoesmith for chemical analysis; D. H. Johnson and D. A. Davenport for aid in statistical analysis; and V. A. Adomaitis, H. F. Duebbert, F. B. Lee, R. E. Stewart, and P. F. Springer for critically reviewing the manuscript.