Breeding Bird Populations in a Proposed Wetland Treatment Area of Northern Minnesota

A census of breeding bird populations was taken in a 40- hectare wetland near Biwabik, Minnesota, prior to the use of this wetland for phosphorus removal from treated wastewater. The wetland was comprised of four distinct habitat types: shrub swamp, black ash (Fraxinus nigra) forest, open coniferous forest, and closed coniferous forest. We used a line transect (about 4 km in length) to document species composition, relative species abundance, and habitat associations of the bird community. A total of816 individuals (mean= 204) and 45 species (mean = 34) were observed during four censuses in June and July, 1985. Two distinct bird communities were present in this wetland: those associated with ombrotrophic habitats (shrub swamp and ash forest) and those present in mincrotrophic habitats (open and closed coniferous forest). The Nashville warbler ( Vermivora ruficapilla) was the most common species in the wetland and also the only species that occurred in both minerotrophic and ombrotrophic habitats. The pre-impact data collected will allow assessment of the relative impact of adding sewage effluent to this wetland and the subsequent effect on bird species and populations