Large-scale habitat relationships of neotropical migratory birds

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Virginia Tech

I examined the relationship of bird assemblages and species to habitat patterns over landscapes composed of a mosaic of habitat elements. I surveyed songbirds using a variation of the variable circular plot method during the 1994 and 1995 breeding seasons on 20 sites ranging in size from 50 to 72 ha on the Quantico Marine Corps Base, VA. Measures of community performance including species diversity, species richness, species equitability, and indices of relative abundance were calculated for each site. I determined the large-scale habitat characteristics of each site by analyzing coverages of each site from Quantico’s GIS database using FRAGSTATS. Landscape patches were defined using 2 different classification schemes to determine if both SAF cover type and generalized habitat classifications could be used to determine which large-scale habitat elements influence bird species and assemblages. I used stepwise multiple regression and stepwise logistic regression to determine which large-scale habitat measures and combinations thereof were associated with high and low measures of community performance.

Diversity as measured by the Shannon-Wiener diversity index and the Simpson’s diversity index was positively related to the amount of high-contrast edge in a landscape in the SAF cover type based analysis. In the generalized habitat type based analysis, diversity was positively related to the number of different patch types per unit area in a landscape and negatively related to the percentage of hardwood forest in a landscape.

The number of different patch types per unit area, the amount of contrast-weighted edge per unit area, and the percentage of mixed pine/hardwood forest in a landscape were selected most frequently as significant predictors of individual species relative abundance in both the SAF cover type and generalized habitat type based analyses.

Habitat diversity was the most important factor influencing the large-scale selection of habitat by bird species on Quantico. With respect to individual species models, the 2 analyses yielded comparable results, and I believe that many of the common bird species occurring on Quantico can be managed according to either the SAF cover type classifications or the generalized habitat type classifications.

songbirds, habitat, Modeling, scale, landscape