Urbanization Differentially Affects the Distributions of Two Sympatric Congeners with Similar Ecological Niches

Abstract

Abstract Urbanization has altered organisms and ecosystems around the world and will continue to do so into the foreseeable future. Although avian responses to urbanization at the community level have been well characterized, we lack species-level studies examining differences in spatial distributions in response to urbanization. We tested for differences in spatial distributions of two congeneric passerine bird species across an urban ecosystem: northern cardinals (Cardinalis cardinalis) and pyrrhuloxia (Cardinalis sinuatus), two closely related songbird species that overlap in distribution. We developed and deployed a new method for testing differences in spatial distributions between species using MaxENT, eBird, and structured bird-survey data across two regions: the state of Arizona and across the Tucson metropolitan area. We then investigated potential urban-environmental factors that may similarly or differentially influence spatial distribution of (a) northern cardinal populations in two urban centers in the state (Tucson and Phoenix) and (b) both species in and around Tucson. We found that northern cardinals occur both further north in the state of Arizona and further into the city of Tucson than pyrrhuloxia. We also found that pyrrhuloxia are excluded from urban areas by habitat availability, but that they are positively associated with human development. High-intensity urbanization has limited urban northern cardinal distributions, and their affinity for areas near open water may have facilitated their northward expansion across the state. We show that species distributions in response to habitat urbanization differ between even closely related species with very similar niches, and characterize environmental associations that drive these differences.