Northern Prairie Wildlife Research Center
University of Saskatchewan, Department of Biology, Saskatoon, SK, S7N 0W0 Canada
Waterfowl depend on abundant and productive wetlands for successful breeding and survival. Wetland quality has often been indexed through measurement of seasonal abundances of aquatic invertebrates, yet assessing aquatic invertebrate availability is labor-intensive and expensive. Because invertebrate abundance is correlated with wetland algal production, the relationship between algal production and waterfowl use was examined to evaluate whether algal sampling might replace invertebrate sampling as a method of assessing wetland quality for breeding waterfowl.
Standing crop biomass (estimated as µg of chlorophyll-a) of epiphytic and planktonic algal communities were measured weekly in six wetlands from April to August 1988. Within each wetland, algae were sampled at open-water sites and at sites within emergent vegetation. Plankton production remained relatively stable throughout the season at 2-6 µg/l, while epiphyte production generally increased to a peak of 25-105 µg/m2 as the substrate was colonized. Algal production varied in a complex fashion both among wetlands, and among sites within wetlands.
Waterfowl use was determined from weekly surveys (morning and evening) and evening behavioral observations. All ducks were counted on each wetland during morning surveys, while evening surveys and behavioral observations focused on dabbling ducks. Analyses with each set of survey data revealed that duck density varied among wetlands and was not directly associated with estimates of production for either algal community. However, time budget analyses revealed that female mallards (Anas platyrhynchos) and blue-winged teal (A. discors) spent a greater proportion of time feeding on the wetland with the highest estimated algal production compared with those feeding on the wetland with the lowest estimated algal production.
Results suggest that measurement of the standing biomass of algae is not a good indicator of wetland quality for waterfowl. Alternatively, the lack of association between algal production and waterfowl use may have resulted from: (1) declining wetland density over the breeding season, possibly masking duck responses to algal production; (2) a lag in the response of invertebrate availability to algal production; or (3) wetlands being of uniformly high quality, possibly presenting ducks with little variability in quality and thus limited ability to exhibit a preference.