Ecology of Blue-winged Warblers, Golden-winged Warblers and Some Other Vermivora

Abstract

Blue-winged Warblers (Vermivora pinus) and Goldenwinged Warblers (V. chrysoptera) have become extensively sympatric in the last 100 years and hybridize where they meet. The two species bred in the same habitats in a study area in central New York, although Bluewings occupied wetter areas to a greater extent than Golden-wings over a three-year period. However, in 1966, when Golden-wings were no longer present, Blue-wings occupied drier areas as well. The two species fed in the same manner and in the same locations. Blue-wings foraged faster and probably slightly more effectively than Golden-wings and hybrids. It is concluded that the two species have very similar ecological requirements, that they are in competition, and cannot coexist indefinitely. Th2 foraging patterns of other members of the genus for which there is information are similar to V. pinus and V. chrysoptera. The bills of Vermivora are very straight and acute at the tip, adaptations for probing buds and leaf clusters and for feeding in flowers. The North American species show some degree of habitat exclusion. Ecological implications for the evolution of the genus are discussed. INTRODUCTION Ecological studies of closely related sympatric species have been of value in testing the hypothesis that two species cannot coexist indefinitely if they have the same ecological requirements (Gause, 1934; Lack, 1944). Closely related sympatric avian species usually differ in habitat (Lack, 1944), method of feeding (MacArthur, 1958; Dixon, 1961), location of feeding (Dixon, 1961; Dilger, 1956; MacArthur, 1958), nature and size of food (Betts, 1955), or are interspecifically territorial (Grant, 1966). Although members of the large warbler genus Dendroica have been the subject of ecological studies (MacArthur, 1958; Ficken, Ficken and Morse, in press), there is little published information on the closely related genus Vermivora, an assemblage of eight North American species and three primarily Central American ones. The purpose of this paper is to describe the ecological relationships of two hybridizing species, the Blue-winged Warbler (Vermivora pinus) and the Goldenwinged Warbler (V. chrysoptera), and to discuss their ecology in relation to their reproductive relationships. The feeding ecology of some other members of the genus is described and related to their evolution. METHODS We observed Blue-winged Warblers, Golden-winged Warblers, and Brewster's hybrids at Varna (Tompkins Co.), New York, in May and June 1961, May through August 1962, and May 1963 and 1966. By 1 Present address: Department of Zoology, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211.