A multi-scale analysis of species-environment relationships: breeding birds in a pitch pine-scrub oak (Pinus rigida-Quercus ilicifolia) community

Analyses of species-environment relationships are critically needed to guide conservation of many declining species. Comprehensive investigations of these relationships must incorporate environmental variables at multiple spatial scales since species responses to the environment vary with the scale of observation. We used partial canonical correspondence analysis to associate a bird assemblage in a threatened pitch pine-scrub oak (Pinus rigida-Quercus ilicifolia) community in Plymouth County, Massachusetts, USA, with plot, patch, and landscape level variables. The first level of analysis partitioned the amount of variance in the bird community explained by plot, patch, and landscape factors from that explained by spatial autocorrelation. The second level partitioned the amount of variance explained by plot, patch, and landscape factors alone and in combination. All three levels of environmental variables together accounted for 43% of the variance in the species data and only 5% of the variance was explainable by spatial factors alone. Landscape level factors accounted for a slightly larger amount of the explained variation (12%) than plot (11%) or patch (8%) level factors. We also examined the cumulative fit of each species to the plot, patch, and landscape partial models. Nine species of regional and/or national conservation concern had distributions that fit one model considerably better than the others. The Great Crested Flycatcher (Myiarchus crinitus) and Black-and-white Warbler (Mniotilta varia) were predominantly associated with plot level factors; the Whip-poor-will (Caprimulgus vociferus) was predominantly associated with patch level factors; and the Purple Finch (Carpodacus purpureus), Gray Catbird (Dumetella carolinensis), Scarlet Tanager (Piranga olivacea), Ovenbird (Seiurus aurocapillus), Brown Thrasher (Toxostoma rufum), and Eastern Kingbird (Tyrannus tyrannus) were predominantly associated with landscape level factors. This study suggests that focusing conservation efforts at the landscape level would provide the most effective protection for the largest number of sensitive species.