| Swainson's warbler (Limnothlypis swainsonii) is a species of conservation concern because of widespread loss of suitable habitat and a small estimated global population. Although research on their habitat requirements has received considerable attention, the species' secretive nature has made examination of its reproductive and social behavior challenging. To learn more about this secretive species and facilitate conservation efforts, from 2006 to 2009, my study examined nest predation and the genetic mating system of a population at the northern limit of its breeding range, in an Atlantic Coastal Plain bottomland hardwood forest at the Roanoke River National Wildlife Refuge, North Carolina. With the help of coworkers, we captured 116 adult and 140 hatch-year Swainson's Warblers and monitored 109 nests.;To increase our mechanistic understanding of the dynamics that influence nest predation, we used infrared video cameras to identify predators of Swainson's Warbler nests. We tested hypotheses concerning the effects of activity, nest-site placement, and ordinal date on nest predation attempts. Black rat snakes ( Elaphe obsoleta obsoleta) and Brown-headed Cowbirds (Molothrus ater) were the most frequent nest predators, while raptors, raccoons (Procyon lotor), and rodents rarely depredated nests. Rat snakes were the most important nest predator overall and during the nestling stage. During the nestling stage, as the breeding season progressed, nests with greater rates of parental activity and with more large trees and more leaf litter in the nest patch had a higher probability of rat snake nest predation attempts. During the egg stage, cowbird predation attempts decreased as the breeding season progressed, but nests with more parental activity and fewer medium-sized trees in the nest patch had a higher probability of cowbird nest predation attempts. Activity factors were more influential on overall nest predation attempts than nest-site placement or ordinal date. The complex dynamics that influenced nest predation are likely site-dependent and highlight the challenges facing managers whose goals include reducing nest losses due to nest predation.;To increase our understanding of Swainson's Warbler genetic mating system, we employed microsatellite genotyping to empirically investigate patterns of paternity. We used four nuclear microsatellites to assess rates of extra-pair paternity and conspecific brood parasitism, and estimated statistical power associated with these markers. We sampled 23 broods for paternity profiling, with the putative mother known for 21 broods. We derived genotypic data for 13 females and their combined 72 offspring and we collected tissue samples from three fetuses from the eggs of an abandoned nest. Brood size averaged 3.1 +/- 0.2 nestlings (range 3--4). We did not detect null alleles, scoring error, or large allele dropout at any of the loci screened. Average expected exclusionary power was 0.946 when the mother was known and was 0.808 when the mother was not known. We identified extra-pair paternity in three broods (13%), indicating that polyandry may not be a common mode of reproduction in Swainson's Warbler. We detected no evidence indicating conspecific brood parasitism. The proportion of broods with extra-pair young that we observed for Swainson's Warbler was low in comparison to six other primarily socially monogamous parulids that have been genetically surveyed and may be due to the habitat configuration at our study site. As the first measurement of extra-pair paternity in this species, our study provides a baseline for future comparative studies as well as studies of geographic variation in extra-pair paternity in this species. |
