68 
THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1. March 2011 
c 4 
■ Bachman's Sparrow 
■ Henslow's Sparrow 
□ Sedge Wren 
■ All species 
Upland (n - 6) 
RCW (n = 6) 
Stand type 
Bog (n = 10) 
DeSoto NatiOTa^ n Fores^M^sissippi. (b ' rdS ^ a ^ ^ ^ ° f win,ering grass,and birds and all species combined r 
Sparrows were not detected in upland stand' 
and densities did not differ between bog an 
RCW stands (F U4 = 0.91, P = 0.36). Sedg 
Wren densities did not differ among stan, 
types (F 2 ,|9 — 0.38, P = 0.69). There were m 
differences in total grassland bird density amoni 
stand types (F 2 , 19 = 3.12, P = 0.068), but densib 
was highest in bogs (Fig. 1). 
PCA of Vegetation Structure.— PCA of the 
vegetation structure variables with the n = 22 dal- 
resuhed in three PCs with Eigenvalues >T 
representing 84% of the variance (Table 1) The 
first PC represented woody understory structure 
and was mostly correlated with all woody 
understory structure variables and herbaceous 
eight. The second PC represented herbaceous 
structure and was mostly correlated with the 
remaining herbaceous structure variables and 
wood, cover CV. The third PC represented ,ree 
density and was mainly correlated with canopy 
closure and tree basal area. py 
f , P f / \°| | lhe nation structure variables with 
with F I' 6 ' (n = 27) reSulted in plrce PCs 
Eigenvalues > 1 , representing 82% of the 
..nance (TaWe 2). PCs followed the pare,™* 
the n - 22 analysis (Table 1). The first PC 
represented woody understory structure the 
second represented herbaceous structure, and he 
t ird represented tree density. PCA of the plant 
species composition guilds resulted in five Pci 
with Eigenvalues > 1 , representing 70% of the 
variance (Table 3). 5 or the 
Vegetation Structure Difference c A e 
Types.— MANOVA revealed 8 
structure PC value differences amn ” Veg ? tatlon 
(Wilks’ X = 023 F. - , a T g D Stand types 
^6, 34 - 6.18, P < 0.001) 
Herbaceous structure was higher in bogs than in 
upland (P < 0.001) and RCW stands (P < 0.001: 
Fig. 2); thus, bog stands had more continuous 
herbaceous cover and patchier woody cover 
There were no significant differences in means 
for the woody structure PC, but RCW stands had a 
lower mean value. The tree density PC was not 
significantly different among stand types. 
Henslow's Sparrow Models. —Henslow’s Spar¬ 
row occurrence was best predicted by decreasing 
herbaceous density CV and increasing cover of 
the sedge Scleria muhlenbergii (Table 4). The 
best model was the only one with AAICc < 2 and 
explained 39% of the relative proportional 
variation. The null model had AAICc = 13.50. 
Parameter estimates for both variables in the best 
model had 95% confidence intervals that con¬ 
tained zero, indicating that, although there was an 
effect, the extent of the effect could not be 
quantified. Abnormally large parameter estimates 
resulting from logistic regression may occur due 
to small sample sizes (Nemes et al. 2009). The 
parameter estimate and standard error for Scleria 
muhlenbergii cover was /? = 10.75 ± 6.67 (95% 
~ ~3.0-24.51). The estimate for the herba¬ 
ceous density CV was p = -0 10 ± 0.05 (95% 
Cl = -0.21-0.02). 
Sedge Wren Models.—Sedge Wren occurrence 
was best predicted by decreasing tree basal area 
an increasing woody understory vegetation 
structure PC values (Table 5). No other models 
^ AICc < 2. The null model had AAICc = 
’ ^ nC - dlC ^ est hi 0 del explained only 17% of 
the relative proportional variation. The parameter 
estimate and standard error for the woody 
understory PC was p = 1.22 ± 0.63 (95% Cl = 
