Urban Environmental Factors Predicting Site Occupancy of Owls In San Antonio, Texas

Date

2024

Authors

Vela, Jose Alan

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Abstract

San Antonio, Texas provides for a unique environment to explore the relationship between its urban features and site occupancy of owls. My study focused on three different owl species, specifically the Great Horned Owl (Bubo virginianus), Barred Owl (Strix varia) and Eastern Screech Owl (Megascops asio). Previously, it has been shown that increased impervious surfaces and anthropogenic noise negatively affect an owl's propensity to occupy an urban site, whereas natural habitat structure increases the probability of an owl to occupy a given site. My study utilized road density to stratify and select survey sites given roadways are associated with anthropogenic noise in an urban area. A total of 52 sites were randomly selected across the survey area and visited three times in 2021 and three times in 2022. At the site level, average tree height (m) was calculated, and environmental noise (average sound pressure level and dominating frequencies) was measured during each survey event. Callback surveys were implemented to increase the probability of detection of each owl. An occupancy analysis was conducted to determine if any variables of interest affected each owl species' probability of detection and occupancy. It was determined that none of the considered variables had an effect on detection and site occupancy of Great Horned Owls. There were no variables that affected the detection probability of Barred Owls or Eastern Screech Owls. As average tree height increased, so did the probability of site occupancy for Barred Owls and Eastern Screech Owls. This study highlights that habitat structure influences some owl's propensity to occupy an urban area.

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Keywords

Habitat, Impervious surface, Occupancy, Owls, Sound, Tree Height

Citation

Department

Environmental Science