Swainson's Warbler (Limnothlypis swainsonii) is a species of conservation concern because of its small wintering range in the Caribbean Basin. relatively low population densities, and habitat fragmentation in its core breeding range in the southeastern United States. We investigated microsatellite DNA variation among I I breeding, populations from eastern Texas to Virginia and two populations from wintering areas in Jamaica and Mexico. Analyses of six polymorphic loci indicated a moderate level of gene flow among breeding populations. relatively small effective population sizes (< 200 individuals in each sampled population), and subtle population variation. We detected no evidence of population bottlenecks in breeding or wintering populations. Bayesian assignment tests suggested that substantial mixing of breeding populations may Occur in wintering areas. Genetic differences between the Mexican and Jamaican populations indicate they may be drawn from different subsets of breeding Populations. Patterns of genetic variation among breeding and wintering Populations Suggest a network of local and regional conservation programs may be necessary to maintain genetic diversity in Swainson's Warbler.
