Behavioral and reproductive consequences of mesopredator activity to grassland birds
Jennifer L. Thieme, MS
Advisor: Amanda Rodewald
Although urban green spaces have the potential to provide valuable habitat to declining species of grassland and early successional birds, they often support greater abundance and diversity of predators than rural lands. High densities of predators may prompt behavioral and/or demographic responses from breeding birds that diminish the conservation value of urban parks. From 2009-2010, I examined how habitat heterogeneity and variation in the predator community influenced the breeding ecology of grassland and early successional birds in urban parks. In general, territory densities were negatively related to predator activity within 2-ha plots, though associations varied across species. As captures of small mammals increased, territory densities of Field Sparrow (Spizella pusilla), Common Yellowthroat (Geothlypis trichas), and Savannah Sparrow (Passerculus sandwichensis) declined. Likewise, mesopredator numbers were negatively associated with Common Yellowthroat and Savannah Sparrow densities. Oddly, snake activity was positively associated with nest survival of Field Sparrows, though negatively associated with that of Song Sparrows. At large scales, vegetation characteristics best predicted nest survival of both species. These results provide evidence that grassland and early successional birds respond not only to habitat structure, but also to activity of potential predators. Consequently, the best management practices in urban parks will both maintain vegetation structure that promotes successful nesting and discourage activities that promote high predator abundance.