Responses of breeding bird communities to human disturbances in upland coastal zones of the Great Lakes
Bird community composition can be used to assess the structural and functional condition of an ecosystem. Categorizing species based on life history traits, similarities in habitat use, nesting, and food requirements is a useful way to evaluate the collective response of different species to changes in environmental conditions. We sampled breeding bird communities in over 200 upland sites within 6 km of the Great Lakes shoreline to determine their responses to human disturbance. Primary human disturbance included agriculture, human population density, and development. Hierarchical partitioning was used to understand the relative importance of land use stress and spatial confounding factors in explaining variability in bird functional guilds. Indices of Ecological Condition (IEC) were used to summarize responses for 33 guilds within the Great Lakes coastal zone in an attempt to develop more robust predictors of stress.
Hierarchical partitioning results indicated that independent effects of land-use stressors were more important than spatial covariates for several functional guilds including foliage, bark gleaning and aerial insectivores, as well as canopy-nesting and area-sensitive species richness. Other guilds and the combined IEC scores had variable responses to stress in the northern and southern ecoprovinces of the Great Lakes; a reflection of the extensive agricultural development and higher human populations in the southern province. Change in resource availability related to human disturbance is evidenced by population declines in guilds dependent on forest resources. Declines in functional guilds represent reductions or losses of important ecosystem processes, such as pollination, seed dispersal, and insect control. Identifying where shifts in community composition occur relative to the proportion of development in the landscape can be useful in regional land use planning, for promoting avian diversity, and potentially mitigating the negative effects of human disturbance. This study demonstrates dominant effects of anthropogenic stress on functional attributes of bird communities over large geographic scales and develops robust indices of stress to be used in biomonitoring at both local and regional scales.