Effects of Supplemental Feeding on Nesting Success in Eastern Bluebirds, Sialia sialis

Graduate #63
Discipline: Ecology Environmental and Earth Sciences
Subcategory: Ecology

Danielle C. Perryman - Oklahoma State University
Co-Author(s): Jennifer L. Grindstaff, Oklahoma State University, OK

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Although humans have well-documented negative impacts on wildlife populations, anthropogenic effects may sometimes benefit wildlife. A potential positive effect is the provision of supplementary food through bird feeders. Problem Statement: Use of supplemental feeders is a direct impact humans may have on wildlife. As a common pastime, there is a disproportionately small amount of research done on the physiological effects bird feeding has on birds. This study fills gaps in knowledge about effects of bird feeding on stress physiology and nesting success through research on a common songbird, the Eastern Bluebird (Sialia sialis). Supplemental food was manipulated in bluebirds by installing feeding cups inside artificial nest boxes prior to the breeding season. Nestboxes were assigned at random to one of three treatment groups. The first experimental group (FULL) was given mealworms from the nest completion stage through the fledging stage for each breeding attempt. The second experimental group (PART) was given mealworms from the nest completion stage until the hatching stage. Upon hatching, no further mealworms were added during that breeding attempt. When additional breeding attempts were initiated in nest boxes, mealworms were again added to the FULL and PART groups, with the PART group again not receiving mealworms after hatching. The control (CTRL) did not receive mealworms at any point. All three groups were visited on the same schedule. I then collected data on nesting success in each group by recording hatching success, clutch size, and nestling growth. Additionally, I collected blood samples to assess stress physiology. Results from the study indicate that there were no significant effects of supplemental feeding on hatching success or offspring sex ratios. In the analyses I have conducted to date, supplemental feeding does not appear to impact the birds either positively or negatively. Further analyses of the effects of supplemental feeding are still needed, particularly analysis of potential effects on stress physiology. In my future research, I will evaluate two of these indirect measures: the steroid hormone corticosterone (CORT), which is the main glucocorticoid in birds, and changes in the leukocyte profile, particularly the ratio of heterophils to lymphocytes (H:L ratio). I anticipate that adding supplemental food will reduce stressors associated with foraging and by doing so, is predicted to reduce CORT levels and H:L ratios.

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Funder Acknowledgement(s): Funding for this research is provided by the OK-LSAMP Bridge to the Doctorate Fellowship Program, Southwestern Association of Naturalists, Oklahoma Ornithological Society, Oklahoma State University Women’s Faculty Council, and funding from the Department of Integrative Biology at Oklahoma State University provided to Dr. Jennifer Grindstaff.

Faculty Advisor: Jennifer Grindstaff, jen.grindstaff@okstate.edu