Man's Influence on Hybridization in Two Avian Species in South Dakota

Abstract

cussed its taxonomic significance. Some have also commented on man's impact on the vegetation of the Great Plains and its significance to hybridization (e.g., West 1962; Short 1965). Recent changes in the vegetation of South Dakota and possible effects of these changes on hybridization of flickers (Colaptes auratus auratus and C. a. cafer) and orioles (Icterus galbula galbula and I. g. bullockii) are considered here. Nomenclature used conforms to the guidelines established by Short (1969) for hybridizing forms. Flickers and orioles occur throughout much of South Dakota. Hybrids are common in the western half of the state and both hybridizing pairs form zones of hybridization, areas in which parental phenotypes make up 5 per cent or less of the population (Short 1969). Both species occur wherever there are tall or moderately tall trees (towns, farm groves, shelter belts, and along streams and rivers). Dominant trees occurring naturally in such areas include cottonwood (Populus deltoides), American elm (Ulmus americanus), ash (Fraxinus spp.), and river maple (Acer negundo). Orioles were found more frequently than flickers in burr oak (Quercus macrocarpa). Flickers, but not orioles, were found in ponderosa pine (Pinus ponderosa). The requirements of flickers for trees in which they can make holes differ somewhat from the nesting requirements of orioles and help to understand the above observations.