Recent avian colonists to the West Indies have expanded their ranges through the archipelago in stepping-stone fashion, occupying virtually all of the available islands with suitable habitat. Consequently, gaps in the distributions of colonists can be interpreted as extinction events. One exception to this pattern is the weakly differentiated population of the Red-legged Thrush (Turdus plumbeus) on Dominica, removed by 600 km and many suitable islands from the nearest conspecific population. Mitochondrial DNA sequences show that the Dominican population is practically indistinguishable genetically from that of Puerto Rico. Large genetic distances among other adjacent island populations emphasize the recent derivation of the Dominican population from Puerto Rico, likely the result of human introduction.