Hybridization in the Red-Eyed Towhees of Mexico: The Populations of the Southeastern Plateau Region

THE extensive and complex patterns of variation resulting from hybridization between the Rufous-sided Towhee (Pipilo erythrophthalmus) and the Collared Towhee (Pipilo ocai) in Mexico have been described in three previous papers (Sibley, 1950, 1954; Sibley and West, 1958). The evolutionary and taxonomic significance of hybridization, with particular reference to birds, has been considered in three additional papers by the senior author (1957, 1959, 1961). Other papers, forming a related series concerned with avian hybridization, are Sibley (1958), Sibley and Short (1959a, 1959b, 1964), Sibley and West (1959), Short (in press), and West (1962). The present paper is based upon new material collected in 1958 in an attempt to clarify the hybrid towhee situation in eastern and southeastern Mexico.