Hierarchical correlates of bird assemblage structure on northeastern U.S.A. lakes

We investigated the factors structuring lake shore bird assemblages of the northeastern U.S.A. using data collected from 158 lakes between 1992 and 1994. The assemblage data were aggregated and standardized to produce assemblage compositions consisting of proportions of individuals employing different foraging, dietary, and migratory strategies. The assemblage data were then re-expressed using compositional analysis techniques and subjected to regression tree analysis to identify environmental correlates over a range of scales. Regionally, human density in the watershed was the most important predictor for the foraging, dietary, and migratory compositions. A combination of anthropogenic and non-anthropogenic factors likely contributed to these broadscale associations because land use was largely confounded with climate and geomorphology. More locally, associations with lake shore residential-urban development were identified as being important for the foraging and dietary compositions, as were associations with lake shore wetlands, but only contingent there being little human development present locally and regionally. Assemblages were associated with increasing local and regional human development such that: hawking, aerial foraging, and ground gleaning individuals increased relative to hover-and-gleaners, foliage gleaners, and bark gleaners; omnivores increased relative to insectivores; and residents increased relative to neotropical migrants. The observed changes in bird community structure were consistent with declines in forest interior species relative to edge species in response to forest fragmentation and suggest that anthropogenic factors have played a prominent role in structuring lake shore bird assemblages of this region.