Brooks and Stouffer • GRASSLAND BIRDS IN PINE SAVANNAS 
69 
TABLE 1. Rotated principal components pattern from a PC A of 12 vegetation structure variables (n = 22) used to 
compare vegetation among three stand types. Values are the correlations of the raw variables with each PC. Highest 
correlations are in bold. CV = coefficient of variation. 
Variable 
Woody PC 
Herb PC 
Tree PC 
Woody cover 
0.896 
-0.268 
0.270 
Woody density 
0.885 
-0.279 
-0.154 
Number stems 
0.857 
-0.305 
0.024 
Woody height 
0.738 
-0.570 
0.157 
Herb height 
0.651 
-0.222 
0.115 
Herb density 
-0.191 
0.935 
-0.125 
Herb cover 
-0.386 
0.835 
-0.035 
Woody cover CV 
-0.571 
0.632 
-0.068 
Herb cover CV 
0.613 
-0.693 
0.276 
Herb density CV 
0.550 
-0.737 
0.072 
Canopy closure 
0.136 
0.091 
0.948 
Tree basal area 
0.009 
-0.378 
0.869 
Proportion s 2 explained 
61% 
14% 
9% 
—0.08-2.51). The estimate for basal area was Bachman’s Sparrows occurred in upland and 
-6.99 ± 3.25 (95% Cl = —13.71——0.28). RCW stands but not in bog stands in our winter 
study. These results support the breeding season 
DISCUSSION observations of Allen et al. (2006), who reported 
Most upland stands supported low numbers of 
grassland birds (< 1 bird/ha), but the presence of 
Henslow’s Sparrows in RCW and bog stands led 
to densities >3 birds/ha. This type of information 
is important because it provides baseline knowl¬ 
edge of which habitat types may be most 
important for birds. Species-specific preferences 
should be considered, however, as two of our 
three study species did not occur in all three stand 
types. Our small sample sizes may have limited 
revealing significant differences between birds 
and vegetation among stand types. 
Bachman’s Sparrows to be more common in 
upland habitats compared to wetter pocosins in 
North Carolina. Haggerty (1998) suggested breed¬ 
ing Bachman’s Sparrows may prefer patchy 
herbaceous ground cover because this facilitates 
prey capture by foraging birds. Cox and Jones 
(2009) reported Bachman’s Sparrow winter abun¬ 
dances at sites in Georgia were positively 
correlated with bare ground and negatively 
correlated with increased grass structure and 
shrubs <1 m in height. Upland stands in DSNF 
have patchy herbaceous cover, and Bachman’s 
TABLE 2. Rotated principal components pattern from a PCA of 12 vegetation structure variables (n = 27) used to 
model Henslow’s Sparrow and Sedge Wren occurrence. Values are the correlations of the raw variables with each PC. 
Highest correlations are in bold. CV = coefficient of variation. 
Variable 
Woody PC 
Herb PC 
Tree PC 
Woody density 
0.902 
-0.166 
0.037 
Woody cover 
0.884 
-0.155 
0.383 
Number of stems 
0.819 
-0.313 
0.055 
Woody height 
0.815 
-0.319 
0.256 
Herb cover CV 
0.693 
-0.553 
0.379 
Herb height 
0.580 
-0.236 
-0.025 
Woody cover CV 
-0.693 
0.468 
-0.158 
Herb density 
-0.163 
0.943 
-0.096 
Herb cover 
-0.480 
0.773 
-0.166 
Herb density CV 
0.529 
-0.755 
0.151 
Canopy closure 
0.122 
-0.031 
0.922 
Tree basal area 
0.118 
-0.230 
0.888 
Proportion s 2 explained 
60% 
13% 
9% 
