The White‐breasted Thrasher (Ramphocinclus brachyurus; WBTH) is restricted to three populations, two on St. Lucia and one on Martinique. The St. Lucian and Martinique populations are separated by ~80 km. The two St. Lucian populations (Northeast and Mandelé) are separated by only 4 km. Little is known about movement of individuals between these three areas; none of the ~500 birds banded in the St. Lucian Mandelé range have been resighted in the other two thrasher populations, though resighting was not the goal of past WBTH work. Evidence from field surveys of banded birds in 2013 suggests that these separate populations might be completely isolated, even those separated by only 4 km – this might be due in part to the intervening matrix of human development and agriculture acting as a barrier to dispersal. In addition to banding records, our research provides a separate method for determining the degree to which populations are isolated by using genetic methods that compare allele frequencies. To do this, we collected blood samples. With these samples, we can assess overall genetic structure, genetic diversity within each population, and number of migrants between populations. Ultimately, these measures will tell us the extent to which each population is reproductively isolated.