A Late Pleistocene Bird Community at the Northern Edge of the Tropics in Sonora, Mexico

Abstract

Recently collected fossils from the late Pleistocene (Rancholabrean North American Land Mammal Age) locality at Térapa, Sonora, México, represent 31 species of non-passerine birds. Twenty-three of the species (74%) are aquatic (grebes, pelican, cormorant, herons, ibis, stork, geese, ducks, rails), reflecting the lacustrine environment (marsh, lake) in which the fossils accumulated. The eight non-aquatic species (harrier, kite, two eagles, caracara, quail, killdeer and owl) suggest habitats from grassland to open woodland to desertscrub to tropical thornscrub. Three species are certainly extinct (the duck Anabernicula cf. A. oregonensis, eagle Buteogallus (Wetmoregyps) daggetti and owl Strix brea). Only the owl has been recorded previously in Sonora. A species of large stork (Ciconiidae sp., genus uncertain) probably is extinct as well. Previously unrecorded in Sonora is a kite Ictinia sp. Among the 26 other species (all extant), four have no modern records within 100 km of Térapa (the ibis Plegadis cf. P. chihi, Canada Goose Branta canadensis, Common Moorhen Gallinula chloropus and Purple Gallinule Porphyrio martinicus). Although the non-passerine fossil bird community at Térapa is dominated by aquatic species with broad latitudinal and longitudinal ranges, five of the eight species of landbirds do not occur north of the southwestern U.S. or northern México. The subtropical biogeographic affinities of the Térapa birds agree with those suggested for the associated reptile and mammal fossils.