• Buteo galapagoensis;
  • Buteo swainsoni;
  • archipelago;
  • island;
  • morphology;
  • niche expansion

Previous phylogenetic hypotheses suggest a sister group relationship between mainland and widespread Buteo swainsoni (Swainson's hawk) and the island archipelago taxon Buteo galapagoensis (Galápagos hawk). We further describe phylogenetic relationships of this clade using molecular data from the mitochondrial control region, and consider the role of niche expansion on phenotype using morphological data from B. galapagoensis, B. swainsoni, and related Buteo jamaicensis (red-tailed hawk). Among 52 unique Buteo haplotypes, phylogenetic analyses support a monophyletic B. galapagoensis clade within a clade of B. swainsoni haplotypes, rendering B. swainsoni paraphyletic with respect to B. galapagoensis. Mitochondrial paraphyly is likely a result of incomplete lineage sorting subsequent to a recent colonization event and exemplifies speciation of peripheral population isolates. Morphological comparisons indicate that metrics associated with prey capture differ significantly between B. galapagoensis and B. swainsoni, but are similar between B. galapagoensis and B. jamaicensis. These results suggest directional selection on B. galapagoensis morphology associated with feeding, possibly an outcome of decreased interspecific competition and change towards a more generalist diet shared by B. jamaicensis. In the B. galapagoensis lineage, our results suggest that genetic drift influences the neutral mitochondrial marker, whereas selection may have driven phenotypic character change. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 779–789.