Nest Site Selection by Western Kingbirds (Tyrannus verticalis) in an Urban Environment
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Urban nest site selection by Western Kingbirds (Tyrannus verticalis) was examined over two breeding seasons in San Marcos, Texas. Within the study area of approximately 70 ha, 45 and 63 nests were identified in 2005 and 2006, respectively. In 2005, 18% of nests were in trees, 75% on utility poles, and 7% on other manmade structures. In 2006, 46% of nests were in trees, 51% on utility poles, and 3% on other manmade structures. To identify environmental variables associated with nest site selection, I recorded nest height, structure height and type (tree or manmade), diameter at breast height (dbh), presence or absence of ground cover or understory vegetation, distances to the nearest street, building, light, tree, and distance to the nearest neighboring Western Kingbird nest. The same variables were recorded at randomly selected unused nest structures within the study area. Logistic regression was performed on 20 a priori models and Akaike Information Criterion corrected for small sample size (AICc) was used to determine which model was best at balancing parsimony and the fit of the data to the models. The reduced dataset (n = 84) used for statistical analyses included 43 nest sites and 41 unused sites. Mean nest height was 8.33 m (SE = 2.30). Mean nest structure height was 11.21 m (SE = 2.10). Mean nearest neighboring distance for a Western Kingbird nest was 68.21m (SE = 32.52). The selected model had an Akaike weight of 0.1762, Nagelkereke’s r 2 of 0.26, and included variables for structure height, presence or absence of ground cover or understory vegetation, distances to the nearest street, building, and tree, and distance to the nearest neighboring Western Kingbird nest. Parameter estimates indicated that nest sites tend to have taller structure heights and no ground cover or understory vegetation, were closer to streets but farther from neighboring Western Kingbird nests, tree canopy edges, and buildings. Understanding the ecological requirements of Western Kingbirds may aid in understanding the success or failure of other avian species in urban habitats.