The Wilson Journal of Ornithology 124(4):721 727, 2012 
LANDSCAPE-LEVEL FOREST COVER IS A PREDICTOR OF 
CERULEAN WARBLER ABUNDANCE 
FRANK R. THOMPSON III, 14 MARK B. ROBBINS, 1 AND JANE A. FITZGERALD 3 
ABSTRACT.—We examined support for the hypothesis that abundance of Cerulean Warblers (Setophaga cerulea) 
increases with percentage of bottomland and upland forest, and decreases with percentage of developed land at a local- 
habitat scale (within a 250-m buffer) and increases with percentage of all forest at a landscape scale (within a 10-km 
buffer). We conducted surveys along 16 rivers in Missouri and Arkansas from 1999 to 2006 and related habitat and 
landscape factors to counts of Cerulean Warblers in 123 5-krn segments on these rivers. We detected 576 singing male 
Cerulean Warblers and found support for both local and landscape effects on Cerulean Warbler abundance. Model fit was 
good with an average correlation of 0,841 between predicted and observed values based on an eight-fold cross-validation 
procedure. The abundance of Cerulean Warblers increased 390.7, X.7. and 4.1 limes across the observed range of forest 
within 10 km. bottomland forest within 250 in. and upland forest within 250 m. respectively. Conservation and research 
need to address large-scale forest patterns in addition to local habitat for Cerulean Warblers. Further research is needed on 
abundance patterns across riparian and upland forests and demographic rales in this part of their range. Received 17 April 
2012. Accepted 19 June 2012. 
There is great conservation concern for the 
Cerulean Warbler (Setophaga cent lea) (Hamel et 
al. 2004). largely the result of range-wide declines 
in their abundance (Sauer el al. 201 1). Loss or 
alteration of breeding habitat has commonly been 
assumed to be a cause of declines; however, little 
is known about their wintering range and threats 
during the non-breeding season (llamel 2000). 
Recent demographic analyses indicated increasing 
overwinter survival would have (lie greatest effect 
on population growth and that increases in the 
amount of forest cover in agricultural-dominated 
landscapes may be required to increase fecundity 
(Buehler et al. 2008). 
Local habitat characteristics associated with 
Cerulean Warblers include mature deciduous 
forest with large trees and heterogeneous canopies 
(Hamel 2000, Jones and Robertson 2001. Roth 
and Islam 20()S. Bakermans and Rodewald 2009. 
Hartman et al. 2009). Heterogeneous canopies 
used by Cerulean Warblers have been associated 
with riparian or bottomland forests (Hamel el al. 
2004. Carpenter et al. 2011). upland forest and 
ridgetops (Dettmers and Bart 1999. Weakland and 
Wood 2005, Buehler et al. 2006, Newell and 
' L'.S. Department of Agriculture. Forest Service, Nonh¬ 
em Research Station, 202 Anheuscr- Busch Natural 
Resources Building. University of Missouri. Columbia. 
MO 65211. USA. 
University of Kansas Natural History Museum and 
Biodiversity Research Center. 1345 Jayhawk Boulevard. 
Lawrence. KS 66045, USA. 
American Bird Conservancy. 14264 Reno Springs 
Road, Reeds Spring, MO 65737, USA. 
‘Corresponding author: e-mail: lrthompson@fs.fed.us 
Rodewald 2011), and timber harvest (Oliarnyk 
and Robertson 1996. Rodewald and Yahner 2000. 
Bakermans and Rodewald 2009. Newell and 
Rodewald 2012). Cerulean Warblers generally 
prefer heavily forested landscapes and are con¬ 
sidered area sensitive. Landscape effects include 
positive effects of percent forest or forested 
wetlands in a I- to 8-km radius and negative 
effects of edge anil open or agricultural land 
(Hamel et al. 1998, Detimers and Bart 1999, 
Thogmartin et al. 2004, Weakland and Wood 
2005, Buehler el al. 2006. Wood et al. 2006). 
Landscape requirements may vary across the 
breeding range and Cerulean Warblers may 
require larger patches iu more fragmented land¬ 
scapes with less forest (Hamel 2000). 
Understanding how habitat and landscape 
factors affect abundance of Cerulean Warblers 
across their breeding range remains a research 
priority (Hamel 2000; Hamel e( al. 2004, 2006; 
Hamel and Rosenberg 2007). Local or landscape 
factors affecting abundance of Cerulean Warblers 
remain largely unstudied in Missouri. This state is 
the western terminus of (he both the Cerulean 
Warbler’s range and the central hardwoods forest 
region, the most important forest region for the 
Cerulean Warbler (Hamel 2000). Past studies 
have spanned micro-habitat to landscape scales, 
but none has directly compared support for the 
importance of local habitat versus landscape 
forest composition. A large proportion of Cerule¬ 
an Warblers breed in riparian forest in portions of 
this species’ range such as Missouri and Arkansas, 
which have been poorly sampled using conven¬ 
tional survey methods (Jacobs and Wilson 1997, 
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