Thompson Bishop et at. • SWAINSON’S WARBLER NESTING ECOLOGY 
729 
this species’ productivity in industrial hardwood 
forests is valuable considering most of tile 
population is likely located on private lands 
frequently managed by timber companies. 
The Swainson's Warbler is in need of manage¬ 
ment and monitoring attention, but the lack of 
available information jeopardizes sound manage¬ 
ment decisions (Graves 2001). Our objectives 
were to: (1) describe nest-site characteristics and 
nesting phenology of Swainson's Warblers, (2) 
assess nesting success in a managed landscape, 
and (3) document the effect of Brown-headed 
Cowbird (Molothrus ater) parasitism on Swain¬ 
son's Warbler nesting success. 
METHODS 
Study Area .—The Woodbury Wildlife Manage¬ 
ment .Area (WWMA; 33 52' N, 79 22' W) is^an 
8,000-ha peninsula at the confluence of the Great 
and Little Pee Dee rivers near Britton's Neck, 
South Carolina. Elevation ranges from 0 to 25 m 
above sea level and includes small isolated 
wetlands, sand ridges, planted loblolly (Finns 
tueda ) and longleaf pine (P. palustris) stands, and 
large expanses of riparian bottomland hardwoods 
(Peters et al. 2005). WWMA bottomlands are 
dominated by broad leaved deciduous trees, 
consisting mainly of sweetgum (Uquiilambar 
styraciflua), red maple (Acer mbrum), and 
ironwood (Carpinits caroliniana) with an under 
story of holly (Ilex spp.). numerous vine species 
le.g.. Campsis . Vitus, Smiiax). blackberry (Rubus 
spp.), and cane (Arundinaria tecta and A. gigantea 
combined into a single classification). Our efforts 
were focused on a 150-ha bottomland hardwood 
stand that experienced drying in late summer to 
early fall, followed by wet winters, and frequent 
early spring flooding lasting up to 25% of the 
breeding season (Martin et al. 1993). 
WWMA was privately owned timberland until 
purchased by the State of South Carolina in 2006. 
Georgia Pacific Corporation harvested the site 
between 1978 and 1983 by shearing all saplings 
and stumps, and then allowed the site to naturally 
regenerate (Peters et al. 2005; Wayne Smith, pers. 
comm.). Even-aged regeneration of hardwoods 
followed clearcuiting with interspersion of uncut 
drainages resulting in a mosaic of young and more 
mature hardwoods (Peters et al. 2005). These 
stands had not been replanted, thinned, or treated 
with herbicides since the last harvest. 
Data Collection.—We began a study that lasted 
five seasons (1999-2001. 2005-2006) starting in 
mid-April and lasting through July. We used spot 
mapping to locate Swainson's Warbler territories, 
followed by systematic nest searches; some nests 
were discovered opportunistically, while conduct¬ 
ing other activities including vegetation sampling 
or mist netting. We used radiotelemetry in 2005- 
2006 to locate nests instead of systematic 
searches. Nest locations were recorded using a 
Trimble GeoExplorcr II. Global Positioning 
System (Trimble Navigation Limited 2001) and 
exported into Arc MAP Version 9.3 (Environmen¬ 
tal Systems Research Institute. Redlands, CA. 
USA). 
Unknown nest outcomes were minimized by 
increasing nest content checks from every 3 days to 
daily nest observation 6 days post hatching. We 
followed Martin and Geupel's recommendations 
(1993) in an attempt to prevent observer-induced 
nest failure, and replaced physical checks with 
binocular observations at -5 or 6 days post 
hatching. Nestlings whose hatching date was 
unknown were classified to age by examining 
leather development (Table 1). The potential 
fledging interval began 8 days after hatching as 
95% of the nestlings fledged after 8 days (Thomp¬ 
son 2005). We were careful not to assign a known 
fate unless one or more fledglings were detected, or 
the chicks reached the potential fledging interval as 
late predation increases the risk of overestimating 
nesting success (Williams and Wood 2002). A nest 
was considered successful if si warbler nestlings 
fledged (Mayfield 1975). 
We collected multiple scales of nest-site data in 
July, at least a week alter fledging, including nest 
characteristics, description of the surrounding 
plot, and neighboring landscape information. Nest 
characteristics included; nest height (base of nest 
to ground), nest cup diameter and depth, outer 
nest diameter and depth, distance of the nest to 
substrate stem, diameter at breast height (dbh) of 
the substrate, and substrate species. All nest 
measurements were recorded from tightly packed 
leaves rather than the furthest leaf margins to 
ensure standardization. We counted the number of 
cane stems at the nest-site scale (5-m radius 
surrounding each nest), and recorded the distance 
of nests to roads, sloughs, and sw amps. 
Data Analyses .—We calculated Swainson’s 
Warbler daily nest survival rate at WWMA using 
two methods: Mayfield's (1975) approach with 
Johnson’s (1979) standard error estimator, and 
Shaffer's (2004) logistic exposure method. Shaf¬ 
fer and Thompson (2007) discourage using 
