Effects of Food and Vegetation on Breeding Birds and Nest Predators in the Suburban Matrix
Jennifer S. Malpass, Ph.D.
Advisors: Amanda D. Rodewald and Stephen N. Matthews
The expansion of urbanization globally has prompted scientists to examine the effects of human developments on wildlife communities, often using birds as a focal taxa. My research investigates population- and community-level consequences of anthropogenic food and vegetation resources in the suburban matrix, focusing on breeding birds and their nest predators. I combine observational and experimental approaches to test how anthropogenic subsidies and habitat modification affect avian population demography and predator-prey interactions, and compare these patterns between developed (i.e. residential yards) versus undeveloped (i.e. forested parks) areas within suburban landscapes.
During April- August 2011-2014, I examined resource availability, and nest predators, and nest survival of two common birds (American robin, Turdus migratorius and northern cardinal, Cardinalis cardinalis) in seven suburban neighborhoods in the Columbus, Ohio metropolitan area. For the first component of my work, I evaluated demographic differences of robins and cardinals breeding in riparian forest parks and adjacent residential neighborhoods and tested if nest predation was higher in yards. Both robins and cardinals experienced similar nest survival rates in residential yards and forest parks, but there were clear differences in which species were responsible for depredation events. Specifically, domestic cats (Felis catus) were over 5x as frequently documented depredating cardinal nests in yards versus forest parks.
For the second component of my work, I tested the hypothesis that wildlife-friendly gardening programs that promote planting trees and shrubs (i.e. increasing woody cover) have the unintended consequence of attracting predators of avian nests by examined relationships between woody cover and diurnal activity patterns of nest predators. Predator activity varied widely among individual yards, but contrary to my hypothesis, the availability of woody cover at either yard or neighborhood scales was not a strong predictor of diurnal activity of five common nest predators.
For the third component of my work, I used observational and experimental approaches to investigate how the most common anthropogenic food subsidy, bird feeders, affected predator-prey dynamics in between birds and nest predators in yards. Bird feeders were positively associated with diurnal activity of two nest predators, but the relationship among birdfeeders, nest predators, and nest survival was complex. Nest survival for robins declined with increasing number of bird feeders but only where American crows (Corvus brachyrhynchos) were most frequently detected. For cardinals, nest survival rates showed no association with either feeder availability or predator activity.
For the final component of my work, I examined the extent to which nest sites in the residential matrix may offer protection from predation by testing the ability of vegetation characteristics of nest sites and features unique to the urban environment (i.e. roads, buildings, and anthropogenic foods) to predict nest survival. I found that nest site characteristics failed to predict nest survival for cardinals and height was the only significant predictor of robin nest survival. I suggest that the lack of relationship between nest site characteristics and nest fate stem from a diverse predator community that effectively precludes any nest site from being predictably safe for birds breeding in the suburban matrix.