Historic distribution of Common Loons in Wisconsin in relation to changes in lake characteristics and surrounding land use

A study was conducted to evaluate changes in water quality and land-use change associated with
lakes that are south of the current breeding range of Common Loons in Wisconsin but that historically
supported breeding loons. Museum collection records and published accounts were examined to
identify lakes in southern Wisconsin with a former history of loon nesting activity. Historical and recent
water quality data were obtained from state and USEPA databases for the former loon nesting lakes that
were identified and paleolimnological data were acquired for these lakes from sediment cores used to
infer historical total phosphorus concentrations from diatom assemblages. U.S. General Land Office
notes and maps from the original land survey conducted in Wisconsin during 1832-1866 and the
National Land Cover Database 2006 were utilized to assess land use changes that occurred within the
drainage basins of former loon nesting lakes. Our results indicate that the landscape of southern
Wisconsin has changed dramatically since Common Loons last nested in the region. A number of
factors have likely contributed to the decreased appeal of southern Wisconsin lakes to breeding
Common Loons, including changes to water quality, altered trophic status resulting from nutrient
enrichment, and reductions in suitable nesting habitat stemming from shoreline development and altered
water levels. Increased nutrient and sediment inputs from agricultural and developed areas likely
contributed to a reduction in habitat quality.