ANN ARBOR---Lakeshore housing development affects breeding bird communities in subtle ways that conventional methods of assessing impact may miss, a study by researchers at the University of Michigan and the Wisconsin Department of Natural Resources suggests. But property owners can take steps to lessen the effects, the scientists say.
Their work appears in the September issue of Biological Conservation, currently available online.
The researchers surveyed breeding birds over a two-year period in an area of northern Wisconsin where lakeshore housing development has boomed in recent years. "The idea was to compare bird communities between pairs of lakes, with one member of each pair being developed and the other undeveloped," says Alec Lindsay, a U-M doctoral student in ecology and evolutionary biology who collaborated on the work with Sandra Gillum and Michael W. Meyer of the Wisconsin DNR. The paired lakes were similar to each other in most other respects, such as size, amount of shoreline, water chemistry and water source.
The researchers canoed to the middle of each lake and picked a shore landing site by using a randomly determined compass bearing. From that landing point, they identified five more landing sites at 60-degree intervals around the lake. At each landing site, they hiked 50 meters inland (except where floating bogs, swamps or other obstacles made that impossible) and counted all the birds they saw or heard in a 10-minute period. They also classified each survey site into habitat categories such as open upland, upland forest, forested lowland, upland rural residential or upland rural commercial.
When it came time to analyze the data from their surveys of 16 developed and 16 undeveloped lakes, Lindsay and colleagues assessed differences in bird communities in a unique way. Instead of simply classifying the birds they saw and heard by species, they also categorized them by "guilds" or ecological groups. In this scheme, birds can be classified by how they feed (on the wing or by poking their beaks into bark, for example), where they nest (on the ground, in trees, on structures), and what they eat (insects, seeds, fish). This analysis of guild structure revealed differences between bird communities of developed and undeveloped lakes.
Specifically, it showed that insect-eating and ground-nesting birds were less common around developed lakes, while seed-eaters were more prevalent. Birds such as loons that are sensitive to disturbance also were scarcer on developed lakes.
Lindsay and colleagues also compared bird communities on developed and undeveloped lakes with measures that typically are used to assess the impact of development or disturbance---such as logging---on wildlife. They looked at abundance (numbers of birds), richness (numbers of species) and diversity (a measure of how evenly distributed among species the birds in a given community are). In contrast, using these traditional measures, they found no differences in bird communities around developed and undeveloped lakes.
"We were surprised that the coarse descriptors [abundance, richness, diversity] were unable to discern the significant impact lakeshore development had on bird communities," says Lindsay. "Had we not done more detailed analyses that considered the ecological significance of birds in these habitats, we would have missed these important but subtle effects of development."
Lindsay speculates that lakeside homeowners' habits of clearing brush, planting lawns, and stocking feeders with birdseed contribute to the differences. Other studies have shown that development leads to increasing numbers of raccoons and domestic cats, which also threaten ground-nesting birds and their eggs.
While there is no harm in luring seed-eating birds to lakeside property, the loss of insect-eaters could cause problems, says Lindsay. Without birds to keep them in check, plant-eating insect larvae, such as gypsy moths and tent caterpillars, could cause serious damage to trees.
What can lake-dwellers do? Keep lawns small, and encourage native vegetation, Lindsay suggests. And keep pets away from areas where birds may be nesting or feeding.
The University of Michigan
Ann Arbor, MI 48109-1399