Carpenter et a/. • CERULEAN WARBLER MICROHABITAT ASSOCIATIONS 
213 
TABLE 3. Best supported logistic regression models for predicting occurrence of Cerulean Warblers. Akaike 
Information Criterion (AIC) values calculated using -21og-likelihood values (L) and K (total number of parameters +1). 
Akaike weights (w,) derived from each model's likelihood (ML) divided by the sum of all ML values. Beta coefficients 
signify a variable’s relationship (+, or ±) to Cerulean Warbler presence. 
Model 
L 
K 
AIC 
AAIC, 
ML 
DECBA(-t-), ASPECT(-). CSTRC(-), GAPDIST(-), 
RBASNG(-). RBATR(+). TRDBH(-t-) 
69.77 
8 
108.00 
0.00 
1.00 
0.87 
RBATR( -). BA(+), TRDBH( + ), L’PHT(-). LOWHT(+), 
MIDHTl -). DECBAH-). NTREE(- J. L'NDSTRY(±), 
CSTRC( -). CCVR(+) 
66.12 
12 
112.00 
5.81 
0.05 
0.05 
RBATRl -i. DECBAI+), CCVR(+). TRDBHI+), 
GAPSZI+). MIDHT(+) 
78.70 
7 
107.00 
6.65 
0.04 
0.03 
RBATRI+). RBASXG(-). DECBA(+), GAPSZ(+). 
GAPDIST(-). CCVR(-), CSTRC(-). TRDBH(+), 
l NDSTRYi ±). LPHTi + 1 
69.47 
11 
111.00 
6.75 
0.03 
0.03 
BA(-). DECBAI+). CCVR(+), ASPECTt- ). TRDBH(+), 
UPHT(-) 
81.36 
7 
107.00 
9.31 
0.01 
0.01 
CCVR(+). TRDBH(-r). UNDSTRY(±), UPHT( - l. 
RBATR(+), DECBA(+) 
81.70 
7 
107.00 
9.65 
0.01 
0.01 
DECBAi+1. NTREE(-). UNDSTRY(±), CSTRC(-), 
CCVR(+) 
85.63 
6 
106.00 
11.32 
0.00 
0.00 
NTREE(-), DECBA(+), GAPSZI+), GAPDIST(-), 
CCVR(+) 
86.48 
6 
106.00 
12.17 
0.00 
0.00 
RBATR(-). BA(+), TRDBH(+), UPHT(-), LOWHT(+), 
MIDHTl-). DECBA(+), NTREE(-), UNDSTRY(±) 
78.98 
10 
110.00 
13.88 
0.00 
0.00 
DECBA(+), NTREE(-), UNDSTRY(-) 
92.69 
4 
104.00 
13.97 
0.00 
0.00 
upland, mixed forests, and edge habitats; how¬ 
ever, Jndigo Buntings and Blue-winged Warblers, 
two species common in shrub and edge habitats, 
were closely associated with Cerulean Warblers. 
These patterns suggest Cerulean Warblers may be 
tolerant of small-scale disturbances within the 
otherwise large, contiguous forest tracts in which 
they are found (Hunter el al. 2001, Jones et al. 
2001, Hamel et al. 2005a, Wood et al. 2005). 
We observed Northern Parulas and Red-eyed 
Vireos reacting aggressively to Cerulean Warbler 
playback and engage in direct physical contact 
with Cerulean Warbler males on several occasions 
(JPC. pers. obs.; Jones et al. 2007). Both of these 
species are common canopy-dwellers in bottom¬ 
land deciduous forests whose resource selection 
likely overlaps that of Cerulean Warblers. We 
detected no difference between counts of common 
nest predators and Brown-headed Cowbird abun¬ 
dance; however, the latter species was plotted 
near Cerulean Warblers along one axis of our 
ordination and may be attracted to the same edge 
habitat Blue-winged Warblers and Indigo Bun¬ 
tings are using. We did not examine these 
relationships in detail but acknowledge that more 
research is needed to learn if abundance and 
behavior of competing, predatory, and brood 
parasitic species are limiting productivity of 
Cerulean Warblers in Alabama. 
We found Cerulean Warblers breeding in 
communities with more individuals and species, 
higher species diversity, and a greater number of 
species of conservation concern compared to 
areas where they were ab.sent. Bird species 
richness and abundance increase as habitat 
patches increase in area and heterogeneity (Free- 
mark and Merriam 1986. Blake and Karr 1987), 
which is characteristic of the forested landscapes 
surrounding our Cerulean Warbler populations 
(Carpenter 2007). Cerulean Warblers were not 
effective bio-indicators for overall species diver¬ 
sity in Ontario, but were suited as an umbrella 
species for similar, canopy-dwelling birds (Jones 
et aJ. 2004). Our results also suggest managing 
forests for Cerulean Warbler habitat may create 
habitat and improve conservation prospects for 
several additional species. 
Many of our results mirror findings from similar 
studies throughout the Cerulean Warbler’s range 
and agree with the general assumptions of Cerulean 
Warbler selection of microhabital characteristics, 
including large diameter trees, less dense understo¬ 
ry, and taller upper canopy (Lynch 1981. Jones and 
Robertson 2001 , Wood et al. 2006). However, some 
