Nest and perch locations of Black-throated Blue Warblers in West Virginia, Virginia, and New Hampshire were examined to determine the structural similarities of the vegetation surrounding these sites and to determine the contribution of each location to the description of the territory. Principle component analysis (PCA) was used to determine habitual variables correlated with the location of the nest and perches. Factors derived from the analyses were combinations of either macro or microhabitat subsets of vegetational variables.

In the nest site analysis, four macrohabitat factors described the presence of major tree species, along with structural characteristics of the overstory and understory. The interaction of overstory and understory was expressed by the density of vegetation in various layers in the nests. The 4 microhabitat factors were concerned with structures within 1 meter of the nest. Pattern analysis of vegetation structure suggests nest site placement depends on the layering of a discrete overstory and on a particular subset of structural variables which are present in the understory across habitats.

Principal component analysis of perch data produced a set of 4 factors describing the contribution of macro and microhabitat variables. Microhabitat factors were highly correlated with the variables DISTANCE FROM TRUNK, LENGTH OF BRANCH, SIZE OF BRANCH, and PERCH HEIGHT. The most strongly correlated macrohabitat variables were BIRCH IMPORTANCE VALUE and % CANOPl COVER. These data indicate males are located at the lower edge of the canopy in mature forests in areas relatively free of understory.

Comparison of these data with similar variables measured at nest sites showed male perches are not correlated with nesting locations. In addition, the variation in habitat models based on perches was twice as large as models based on nest sites.

When male Black-throated Blue Warblers obtain a territory, habitat is incorporated which is used by the female for nesting, but not by the male for singing or foraging. These nesting sites have less variation in the vegetation surrounding them than perches utilized by the males.