The proximity of urban green spaces to anthropogenic food sources can promote high densities of predators that may negatively affect breeding birds. Not only can high numbers of predators depress reproduction and survival, but birds may behaviorally respond by avoiding those patches, thereby diminishing the value of urban habitats. During 2010 and 2011, we examined relationships between avian territory density and activity of nest predators in 36 2-ha plots within six urban grassland and early successional parks (sites) near Chicago, Illinois. At the plot (i.e., local) scale, densities of common yellowthroats (Geothlypis trichas), field sparrows (Spizella pusilla), and savannah sparrows (Passerculus sandwichensis) were more strongly linked to habitat characteristics than predators. Song sparrow (Melospiza melodia) and eastern meadowlark (Sturnella magna) densities were not associated with habitat at the plot scale, but together were negatively related to activity of avian predators. Surprisingly, densities of song sparrows were positively associated with snake activity at both plot and site (i.e., landscape) scales, and densities of savannah sparrows increased moderately with activity of mesopredators at the site scale. Our results suggest that although habitat structure is a strong predictor of grassland bird densities in this urban matrix, activity of predators also may contribute to patterns of territory selection of certain bird species. With this in mind, managers encouraging settlement of grassland birds within urban preserves may consider (a) increasing dense groundcover that provides protective cover for songbirds, and (b) discouraging activities that promote activity of avian predators, particularly corvids.
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Vol. 35 • No. 4