Niche Relationships among Some Deciduous Forest Flycatchers

Abstract

EXPLOITATION of a common environmental resource by several species implies overlapping niches and strongly suggests competition among the species. A variety of strategies have evolved enabling sympatric organisms to partition environmental resources effectively and thus maintain longterm normal population levels. For example, four types of Anolis lizards studied by Schoener (1968a) coexist with differences in body size, in choice of perching and basking sites, in selection of prey items, and in the manifestation of various degrees of sexual dimorphism. Among mammals, different food choices and slight habitat differences seem to be important features permitting coexistence among ecologically similar bats (Tamsitt, 1967) and among carnivores (Rosenzweig, 1968). Kendeigh (1945) and MacArthur (1958) reported stratal selection among sympatric warblers (Parulidae) breeding in tall coniferous forests. However, in forested communities of lower relief and in nonforested communities where vegetational stratification is much less apparent, segregation of avian species with similar niche requirements has received relatively little attention from ecologists (but see Cody, 1968; Orians and Horn, 1969), despite the increased interest in these ecological problems. An intriguing avian feeding niche is flycatching, conventionally associated with North and Central American Tyrannidae because many of these flycatchers typically procure flying insect prey by periodic aerial sorties from stationary perches. In an earlier investigation Hespenheide (1964) made note of some interspecific competitive features between sympatric species pairs of Tyrannus, and further suggested intergeneric differences in habitat and nest site selection for other tyrannids. The present study on flycatchers was undertaken in a region where five species are geographically sympatric and with the objective of analyzing the separate and corporate ecologies of the species to determine the factors permitting their successful coexistence.