| Summary: | Foraging habitats and foraging behavior for seven species of Tyrannid flycatchers were measured to examine interspecific habitat resource partitioning, niche breadth and niche overlap. Four of the species inhabited forested areas; Great Crested Flycatcher, Eastern Wood Pewee, Least Flycatcher and Acadian Flycatcher. Two species, the Eastern Kingbird and Willow Flycatcher, were found in open habitats and one species, the Eastern Phoebe, was found in both open and woodland habitats.
Among forest species of flycatchers and open habitat species there was considerable similarity in vegetational characteristics of the foraging habitat. Contrary to previously published studies, these similarities contributed to a high degree of resource overlap among syntopic species of forest flycatchers. A similar degree of overlap was also observed among the open habitat species. Much of the resource overlap among species was attributable to the large resource (habitat) breadth of the Willow Flycatcher and Eastern Wood Pewee.
Overlap in foraging habitat among the species was reduced by their using other means of resource partitioning within habitats. Most notably, vertical stratification effectively separated most forest species. The use of different foraging substrates and different foraging tactics (sortie flight distance and methods of insect capture) were also important means of partitioning the food resource.
Data were analyzed to test a previously published hypothesis which indicated that the foraging ecology of a smaller flycatcher species was affected by the presence of a larger syntopic competitor. To test this hypothesis, the Willow Flycatcher and Eastern Wood Pewee were selected because they had large resource breadths (ecologically plastic) and because sampling for both species included habitats which were syntopic and nonsyntopic with their respective competitors, the Eastern Kingbird and Great Crested Flycatcher. Both smaller species displayed a reduction in resource breadth in areas of syntopy. Therefore, these data tend to support the published hypothesis and indicate habitat accommodation on the part of the smaller species, in the presence of a larger competitor. === Ph. D.
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