| Conservation plans for the southeastern U.S. have identified Swainson's Warblers (Limnothlypis swainsonii) to be among the more vulnerable Neotropical migrants. However, a lack of life history information, in particular breeding, jeopardizes sound management decisions. My study examined a population in Britton's Neck, South Carolina on timberland owned by International Paper Co. From 1999--2001, I conducted a breeding biology study that examined nesting, territory, vegetative, and landscape characteristics.;I discovered 98 SWWA nests, 63 of which were active. SWWA nesting success equaled 60% using the Mayfield success estimator. Contrary to the notion of SWWA requiring mature forests to breed, SWWA bred successfully in 20-year old regenerating clearcuts. Multiple brooding, where a pair initiates nesting attempts after their first is successful, was detected in 20% of the pairs. An individual's seasonal fecundity was doubled by multiple brooding, increasing the young per female from 1.5 to 3.7. Brown-headed Cowbirds (Molothrus ater) parasitized only 10% of nests. No SWWA chicks were observed fledging in the presence of Cowbirds.;Apparent population density was 17 territories/km2, equaling the highest density ever recorded for SWWA. One-fifth the site contained 59 territories/km2, compared to the remaining four-fifths with 12 territories/km2. I examined vegetative differences between nests built in high- versus low-density areas using a discriminant function analysis (DFA). The DFA results indicated understory thickets accounted for the largest difference between high- and low-density nest sites. Nests in the high-density area were more associated with understory thickets.;Using digital photogrammetry, I compared the position of understory thickets and hydrologic features at nest, territory, and unused habitat. Understory thickets were delineated from leaf-off and leaf-on photographs using a spectral analysis and Stereo Analyst, respectively. From the Stereo Analyst classification, SWWA selected nest sites in closer proximity to understory thickets compared to points in territories or unused habitat. Understory thickets at nest sites were larger than those found in the territory or surrounding habitat, and nest understory thickets were two times larger in the high- versus low-density area. |
