Delivery rates and prey use of mountain bluebirds in grassland and clear-cut habitats

Abstract

Clear-cutting of forests results in early successional stages that resemble grasslands, and grassland birds such as Mountain Bluebirds (Sialia currucoides) may settle in these anthropogenically created habitats to breed. Our objective was to determine if parent bluebirds provisioned offspring differently, in terms of amount and quality of prey, in clear-cuts versus grasslands, and how this related to fledgling production. We placed microcameras inside 92 nestboxes during two breeding seasons to film parental food deliveries at sites in central British Columbia. At the young nestling stage (< 5 d old), there were no significant differences in terms of provisioning rate or the type of prey delivered. Neither the abundance of perches in the habitat nor parental traits such as age or plumage brightness were associated with provisioning. When nestlings were older, parents in clear-cuts delivered slightly larger prey and diets with proportionately more larvae and spiders, the most nutritious taxa. However, delivery rates were 21% higher in grasslands than in clearcuts. Fledglings in clear-cuts had lighter body mass than those in grasslands, suggesting that the high nutrient content of prey in clearcuts could not compensate for the lower deliveries. Thus, parents in grasslands seem more able to meet the energy demands of large nestlings by incorporating diverse insect taxa into their diet.