Canyon Wren Territory Occupancy and Site Attributes in Northern Colorado

Abstract

In this study we examined patterns of habitat occupancy by canyon wrens (Catherpes mexicanus), an insectivorous, cliff-obligate bird species, in Northern Colorado. Canyon wren territories are generally large and widely spaced, and it is currently unclear if their densities are limited by the availability of cliff habitats that have particular biotic and/or abiotic attributes. We used playback of conspecific song to survey 138 cliff sites and found 23 occupied territories, confirming the species occurs in low densities. Using a model-fitting approach, we assessed the importance of seven factors hypothesized to be important to canyon wren territory settlement and found occupied territories had cliffs that were more likely to be overhung, rather than vertical. Habitat occupancy of canyon wrens was also associated with the presence of cliff swallows (Petrochelidon pyrrhonota) and their nests, with canyon wrens observed nesting and foraging within cliff swallow nests throughout the year. As no abiotic factors predicted both the presence of canyon wrens and cliff swallows, we suggest the biotic resources provided by cliff swallows might be important in driving patterns of canyon wren territory occupation. If canyon wren settlement patterns are affected by the presence of cliff swallows, this system could represent a rare case of heterospecific attraction, where a migratory species (cliff swallow) drives patterns of habitat occupation by a non-migratory species (canyon wren).