We assessed interspecific ecological relationships between Say's (Sayornis saya) and Eastern (S. phoebe) phoebes at three scales by developing ecological niche models at two spatial extents and comparing the models' predictions with data from local-scale surveys. The two species' habitats differed in several environmental attributes, primarily precipitation, temperature, and vegetation indices, at both extents. Local-scale surveys between -97° and -101° longitude revealed a steep gradation in ratios of occurrences Say's to the Eastern Phoebe, increasing from east to west. Local-scale occurrences coincided with results of ecological niche models at the extent of both the continent and contact zone, except for Eastern Phoebe occurrences and vegetation indices at both extents. Say's Phoebes nested in open country with sparse or no surrounding woodland, whereas Eastern Phoebe nests were primarily along woodland streams but also at seven sites in more open country where Say's Phoebes had nested previously. At the contact-zone extent, the niche space of the Eastern Phoebe was embedded more into that of Say's Phoebe than the converse. Although niche models at the contact-zone extent indicated some potential for contact, competition between these two species for nest sites is probably less important in limiting distributions than are autoecological characteristics.
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Vol. 113 • No. 2