Population Genetics and Morphometrics of Overwintering Swamp Sparrows (Melospiza georgiana) at Panola Mountain State Park

Ashley McMahon, Georgia College & State University


Grassland birds are facing the greatest decline of any bird guild in North America due to widespread loss of grassland habitats. Conservation efforts tend to focus on birds that breed in grasslands, but grassland habitat loss will also negatively affect populations that overwinter in grasslands. Three Swamp Sparrow subspecies (Melospiza georgiana georgiana, M. g. ericrypta, M. g. nigrescens) segregate on at least some of their breeding grounds but may mix on wintering grounds, which often includes grasslands. Philopatric passerines often also segregate by sex on wintering grounds. Thus, loss of overwintering grasslands may disproportionately impact both subspecies and sex, leading to declines in one or more subspecies and/or skewed sex ratios during the breeding season. Unfortunately, neither subspecies nor sex are easily distinguishable in the field. Many Swamp Sparrows overwinter at Panola Mountain State Park (PANO), a restored grassland, in Stockbridge, Georgia. The goals of our study are to 1) determine subspecies and sex of birds captured at PANO and 2) identify morphometric measurements that can be used to identify sex and subspecies in the field. We have been capturing overwintering Swamp Sparrows at a year-round banding station at PANO since September 2018. Upon capture, we measure culmen width, culmen length, skull length, skull width, and tarsus length and take a small blood sample by toenail clipping. To date, we have collected 261 samples from 233 individuals. Using microsatellite sex-linked markers specific to subspecies, we will determine sex and subspecies of all samples. We will then perform multivariate analyses to determine which morphometric measurements can be used in the field for sex and subspecies identification. Knowing the sex and subspecies of individuals overwintering in grasslands like PANO can help inform management decisions about where to concentrate grassland bird conservation and restoration efforts outside the breeding season.