Urbanization can fundamentally change the ecology of an area and impact breeding bird populations. For example, increased human disturbance has been shown to negatively affect the fitness of several bird species. Therefore, predicting how urbanization will lead to changes in anthropogenic disturbance regimes is an important component of understanding how human-altered environments will impact natural bird populations. Here, we investigated whether impervious surface cover predicts patterns of anthropogenic disturbance and variation in house wren (Troglodytes aedon) fitness at sites around Williamsburg, VA. We collected temporal and spatial disturbance data at 57 bird nest boxes and generated multivariate measures of these disturbance regimes using Principal Components Analysis. Using GIS, we digitized impervious surface cover within 100 meters of each box (i.e. the breeding territory around each box). Impervious surface area strongly predicted overall temporal disturbance. In addition, several types of impervious surface (e.g. buildings, roads, pathways) predicted specific types of disturbance (e.g. vehicles, pedestrians, cyclists). For 20 of the 57 boxes we studied, we also recorded three fitness-related parameters of the house wrens: brood condition, brood growth rate, and number of chicks fledged (i.e. productivity). These fitness parameters were related to types of impervious surface cover in a reasonably intuitive manner. For example, bicycle and pedestrian disturbance negatively correlated with brood condition. Similarly, total parking surface area was negatively related to number of chicks fledged. Therefore, our study indicates that relatively straightforward measures of impervious surface cover can predict impacts of human development on bird populations. We intend to extend this approach to house wrens in different localities as well as to other avian species.
For additional documentation Louise Gava and Pacifica Summers provided a PowerPoint Presentation entitled "Quantifying Relationships Between Impervious Surface Cover, Disturbance, and Breeding Productivity in Troglodytes aedon" provided here in PDF form.