Date of Award
Program or Major
Master of Science
The Saltmarsh Sparrow (Ammodramus caudacutus) is one of the few species globally that is exclusively restricted to coastal wetlands. Despite the high vagility characteristic of avian species, the highly patchy distribution of tidal marshes can often lead to fine scale genetic structure in salt marsh obligates. To elucidate patterns of population structure, we investigated the degree of genetic differentiation among nine Saltmarsh Sparrow populations along the northeastern coastline of the United States. Although overall FST values were small (0.008), population substructuring was detected along with a positive correlation between geographic distance and genetic differentiation, suggesting that Ammodramus caudacutus follow an isolation by distance model. However, Chapman's Landing was a distinct outlier despite its close proximity to other sampled marshes, indicating that additional factors other then geography play a role in genetic structuring. To identify patterns of source/sink dynamics, we implemented assignment tests from the software program GENECLASS2 using an exclusion method. Results from the assignment tests indicate that Parker River, in Newburyport, MA, is a source population. Findings from the genetic analyses were combined with field data collected on nesting success and density of breeding adults to correlate overall productivity of the sites sampled with results from assignment tests. Furthermore, results from point count surveys indicate a positive correlation between marsh size and the density of breeding adults (P=0.0148, R 2=0.8954), with the most birds observed at points located in Parker River. Results from our nesting study indicate that nesting success is variable among sites, and that the cause of chick mortality also varies. Despite this the percent of failed nests is comparably similar among four of the five sites surveyed. Our results offer new insight for conservation strategies, including information on population clusters, data on population trends, and the identification of source/sink dynamics.
Walsh, Jennifer, "Patterns of population structure and productivity in Saltmarsh Sparrows" (2009). Master's Theses and Capstones. 504.