Migration and Winter Distributions of Canvasbacks Staging on the Upper Mississippi River

Abstract

Fall and winter distribution patterns of canvasbacks (Aythya valisineria) staging on the upper Mississippi River near LaCrosse, Wisconsin (navigational Pools 7 and 8) and Keokuk, Iowa (Pool 19) were studied during 1973-77. Sightings and recoveries obtained from 1,488 color-marked males during 1973-75 and 3,789 banded males and females during 1973-77 suggested 2 principal migration corridors: 1 extending eastward from Pools 7 and 8 to the eastern Great Lakes and southeast to the Mid-Atlantic Region and another southward from Pools 7 and 8 to the lower Mississippi Valley, Gulf Coast, and east Texas regions. These discrete populations stage concurrently on Pools 7 and 8 during the fall, but winter in different areas of the Atlantic, Mississippi, and Central flyways. Populations staging on Pool 19 were not discrete from those staging on Pools 7 and 8. A continual turnover of birds passing through these staging areas was indicated. Canvasbacks wintering in the Mississippi and Central flyways were widely dispersed among a variety of habitats, whereas canvasbacks wintering in the Atlantic Flyway were concentrated in a few traditional habitats. Canvasbacks exhibited strong fidelity to wintering areas. Distribution patterns and population attributes of canvasbacks during fall and winter may be explained by the predictability of natural foods and their ability to exploit these foods. J. WILDL. MANAGE. 47(3):741-753 Principal migration corridors of canvasbacks have been described by Stewart et al. (1958), Geis (1959), and Bellrose (1968). The eastern continental population of canvasbacks was reported staging during fall on Lake Christina and Heron Lake in Minnesota (Smith 1946); Lakes Poygan, Koshkonong, Butte des Morts, Winnebago, and Winneconne in Wisconsin (Jahn and Hunt 1964); the Detroit River, Lake St. Clair, and Saginaw Bay in Michigan (Martz et al. 1976); and the Illinois River in Illinois (Mills et al. 1966). Canvasback use of these traditional staging areas declined dramatically from 1955 to 1966, during which time use of the upper Mississippi River, particularly navigational Pools 7, 8, and 19, increased (Mills et al. 1966; J. H. Stoudt, unpubl. rep., North. Prairie Wildl. Res. Cent., Jamestown, N.D., 1970; W. E. Green, unpubl. rep., Upper Miss. Fish and Wildl. Refuge, Winona, Minn., 1974). The effects of siltation, pollution, eutrophication, and rough fish on such preferred foods as fennelleaf pondweed (Potamogeton pectinatus), American wildcelery (Vallisneria americana), and fingernail clams (Sphaeriidae) have been cited (Mills et al. 1966, Trauger and Serie 1974) as causal factors responsible for the disappearance of canvasbacks from formerly important staging