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.

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SynopsisDirect observations of young-of-the-year brook charr, Salvelinus fontinalis, in a second-order woodland stream indicated that most of their feeding effort was directed toward sub-surface, drifting prey (83% of feeding time) . Feeding from the substrate and water surface was much less frequent (17% of feeding time) . Comparisons of gut contents to drift net and substrate fauna samples corroborated that the most commonly consumed prey (chironomid and trichopteran larvae, ostracods, and ephemeropteran nymphs) were captured primarily from sub-surface, invertebrate drift . The disproportionate numbers of some prey species in the guts of several fish indicate that some prey selection occurred . Territories appeared to be cardioidshaped, and were often contiguous, with dominance hierarchies evident among the residents . Agonistic interactions were frequent . Charges and chases predominated (91% of interactions) while lateral displays were infrequent (9% of interactions) . Overall, these fish spent most of the daylight hours station-holding (77%) and feeding (18%) . While only 3% of total time was spent in aggression, this amounted to 14% of the time a fish spent away from its station . There was some indication that territories were defended at a cost of feeding time .

Water temperatures were constant across the interface through much of the year. By mid-summer, hypoxic conditions prevailed within the water column in the cattail stand. Algae levels were similar across the interface throughout much of the year, with peaks occurring just inside the interface in June and July. Early in the season, there was a trend for higher nektonic invertebrate numbers within the cattail stands of both bays. By late August, there were similar total invertebrate numbers across the interface. Cladocera and ostracod numbers were higher within the cattail stands during June and July; during the same periods, corixid levels were higher in the open water sites. The low oxygen levels within the cattail stands during the summer may reduce predation by fish and other predators that cannot tolerate low oxygen levels. This may explain the higher numbers of prey species like cladocerans and ostracods within the cattail stands during mid-summer. The presence of algal or detrital food resources seemed to have little influence on invertebrate abundance across the interface during this study. Peaks in invertebrate abundance did not occur at the emergent vegetation-open water interface during any of the sampling periods in this study. The high invertebrate diversity and abundance in interspersed wetland habitat may be related more to the mixture of habitat types rather than the amount of interface present.

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 deepwater 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.