Alsup, Steve E. – Productivity and habitat features of Swainson’s Hawks (Buteo swainsoni) nesting in suburban and agricultural areas of Southwest Idaho. 2012.
I compared nesting success and productivity of Swainson’s Hawks nesting in suburban and agricultural areas in southwest Idaho to assess the effects of land use change on Swainson’s Hawk reproduction. I also evaluated habitat parameters and land use patterns around nesting areas to determine if nest site, habitat, and/or landscape features were related to reproductive success in Swainson’s Hawks. I recorded habitat characteristics, nest tree characteristics, distances to four habitat features, and disturbance types, as well as land use patterns within a 1500m radius around nest trees to assess any differences in nest site characteristics, habitat features, and/or landscape features between Swainson’s Hawk territories in suburban and agricultural areas. During 2007 and 2008, I monitored nesting success and productivity of 74 breeding attempts. For both years combined, nesting success was higher in suburban areas (88.9%) than in agricultural areas (71.1%), and the difference approached significance. I found no significant difference in the number of young fledged per laying pair between the two areas; however, brood size at fledging was significantly higher in agricultural areas. Separate univariate logistic regression models for both nesting success and productivity showed negative associations with increased percent of uncultivated land within the nesting buffer, increased distance to water, and increased distance to dwelling. AICc model selection indicated that a model with the single predictor variable (distance to water) was the best predictor of nesting success. Distance to water was included in the top 14 models produced by the model selection process, and after evaluating other predictor variables included in the top models, I found that including additional variables did not increase the predictive power.
My results indicate that Swainson’s Hawks are able to reproduce successfully in suburban areas despite reductions in foraging areas due to human development. However, pairs nesting in suburban areas may suffer from reduced brood size at fledging, indicating that there are some reproductive constraints associated with nesting in suburban environments, such as increased energetic demands associated with increased distance to foraging areas, lower prey delivery rates, and the possibly of brood reduction.