734 THE WILSON JOURNAL OF ORNITHOLOGY . Vol 124. No. 4. December 2012 
represents temporal variability in success or is an 
artifact of limited sample size (n = 17 ). The 
combined effects of nest age. Brown-headed 
( owbird parasitism, nest stage, and distance to 
the nearest swamp had the greatest effect on 
Swainson’s Warbler nest survival in our study. 
Brown-headed Cowbirds may follow swamp edges 
to gain access into forest interiors explaining the 
negative association between swamp edge and nest 
survival: however, cowbirds can also use roads and 
sloughs for the same purpose, but proximity to these 
features did not affect nest survival in our study 
Bc-nson el al. (201 IJa (observed a similar decrease in 
Swam son s Warbler nest survival with age, an 
observation that could be attributed to increased 
act.vuy around nests as nestlings become older. 
One of the most important determinants of 
Swa.nson s Warbler nest success was whether or 
not the nest was parasitized. Not only did the 
presence ol cowbirds reduce the hatching rate of 
eggs m parasitized nests by 27%, it also (/> < 
0 . 001 ) reduced fledgling production by 89% (() ->* 
r,."' 5 flcd 5 l,n «* P cr nest). Our estimate of 
fledgling production in parasitized nests is liberal 
nes,Ii "S s we™ not rcobserved M 
T ‘ nle " SiVe sea rching. Hc„ so „ et 
al. (-01 Ob) observed a similar reduction in 
Swamson s Warbler fledglings at nests in Ark-in 
;™ vs - r 75 nedg,ings ^ 
paras,t.sm status to be the most imporfml 
predictor ot fledgling product!on. SwttLon's 
Warblers can produce fledglings in singly „ ara 
nized nests. bu, a, a much diminished r e 
(Benson et al. 2010b,. They appear be 
particularly vulnerable to Brown-headed Cowbird 
parasitism. Parasitized nests may also be Ta 
greater depredation risk due to increased provi* 
stoning rates of parents (Pappas el al. 2010^ 
JTcmZT ° n " e S ' VainSon ' s Warbler nests 
o.wb,rd"'otTudr::fs ) b LdT' hL ' iA i 
studies at the wpsior,, „i y wh ereas, 
n k s “ sas (36%: eT a r20l0b) re L V “ riable: 
!. “«r m> SSS 
a critical habitat component i ,s 
IQSn ti nun (Lddlenian ei jiI 
>980, Thomas e, al. ,996). However, habitat 
requirements of core breeding populations in 
Georgia and South Carolina may differ. Graves 
(2002) found no cane at a site in Louisiana with 
the highest Swainson’s Warbler population den¬ 
sity on record, and also observed less cane in 
territories compared to non-use plots in the Great 
Dismal Swamp (Graves 2001). We observed 
Swamson's Warblers using a variety of substrates 
foi nesting with vines being most common 
followed by cane. Cane was used as a substrate 
at more than one-third of the nests and was found 
m close proximity to two-thirds of the nests. Daily 
nest survival rates were not influenced by the 
amount of cane in the surrounding area orthetvpe 
°' neslin S substrate used. Lanham and Miller 
(_006) observed mountain populations using 
hemlock (Tsittfa spp.) for nesting. The diversity 
ol Holistic results related to Swain son's Warbler 
labitat pieference may indicate the importance of 
vertical structure to habitat occupancy. 
A major factor influencing Swainson's Warblers 
is hydrology as it is the driving force behind 
vegetative distribution, soil composition, and litter 
launa in a bottomland hardwood forest < Martin et al. 
D.l). Hydrology directly impacted nesting phenol- 
<»gy with May flooding events delaying nest 
initiation by as much u.s 3 weeks in 1999 and 
affecting the abundance of leaf litter. Anich and 
Raley (2010) observed Swainson’s Warblers feed¬ 
ing in novel ways during a flood and suggest this 
species may have evolved the flexibility to survive 
temporary flooding, and continue reproduction. 
ew investigators have examined the litter 
Guna ol floodplain Zones II through V (Martin 
el al. 1993). and more research is needed to 
compare Swainson’s Warbler distribution to 
invertebrate abundance (Brown 200S. Savage et 
al- -010). Several studies (Graves 2001. 2002 : 
Benson et al. 2010b) have examined the effects of 
oo ing on occupancy patterns by Swainson’s 
Warblers, and found them to be profoundly 
impacted due to their characteristic ground 
foraging and shrub nesting life history. Not only 
l ' lc Swamson’s Warblers negatively impacted by 
flooding (Anich and Reiley 2010, Benson and 
e narz 2010), but fewer understory-dependent 
'’lit '- aie found in the frequently flooded zones 
Wlen j° ni P ared to lllc bird communities of higher 
giound (Wakely and Roberts 1996). 
CONSERVATION IMPLICATIONS 
Gin results suggest industrial forests can be 
°i uctive areas tor Swainson’s Warblers. Not 
