Avian habitat selection and prairie wetland dynamics: A 10-year experiment

Abstract

Northern prairie wetlands play a vital role in the life cycle of a wide array of bird species. Prairie wetlands used by birds span the entire range from shallow ephemeral ponds inundated for short periods each spring to large permanent water bodies that seldom, if ever go dry The objective of this study was to determine the response of blackbirds waterfowl, and American Coots to changes in habitat structure induced by water level fluctuations in prairie wetlands. The study was conducted on a series of experimental marshes within the Delta Marsh in southern Manitoba, Canada. Water levels were adjusted following a predetermined schedule to simulate the wet-dry cycle of prairie marshes. Aerial photographs were taken annually and habitats were characterized using Geographic Information System (GIS) techniques. Weekly avian censuses were related to habitat features using Principal Components Analysis (PCA) procedures. Yellow-headed Blackbirds selected shallowly flooded habitats with a mixture of open water and emergent vegetation, while Red-winged Blackbirds were found in shallower areas with dense vegetation. Coot habitat was consistent over the seasons. They preferred deep-water habitats with interspersed vegetation. As a group, dabbling ducks were generally found in hemi-marsh conditions (equal amounts of cover and water in an interspersed pattern) throughout much of the year. Some species moved to deeper, more open habitats during the fall season. As a group, diving ducks chose areas with deeper water and less vegetation than dabbling ducks. However, there was considerable variation among diving duck species, with Canvasbacks using hemi-marsh sites in spring, and Ruddy Ducks and Lesser Scaup using the most open sites found on the study areas. The wet-dry cycle characteristic of prairie marshes presents a wide array of habitat conditions for avian species. Although hemi-marsh conditions during the cycle result in maximum use for a large number of species, they do not meet the requirements of all species in all seasons. Conservation programs should include wetland complexes of varying water depth and flooding duration to ensure the widest array of habitat types for avian species.