A common anthropogenic influence on wildlife is the use of supplemental bird feeders. Dependent on abundance and natural food availability, this supplemental food source could influence individual survival and productivity. In this study, supplemental food availability was experimentally manipulated in a wild population of Eastern Bluebirds, Sialia sialis, to examine the influence of bird feeding on nesting success, especially when supplemental feeding is inconsistent. Adult and nestling bluebirds were assigned to one of three groups. In the first group, birds received mealworms (Tenebrionidae larvae) throughout the breeding attempt. In the second group, birds received mealworms from nest completion until nestlings hatched. Birds in the third group received no supplementation but were disturbed at the same frequency as birds in the other two groups. Nestling growth and reproductive success were calculated to examine differences resulting from the experimental manipulation. Finally to determine if differences in habitat quality contributed to the effect of food supplementation on bluebird nest success, data on invertebrate abundance were collected on a subset of territories.
Nestling mass, tarsus, and wing chord length were not significantly affected by experimental treatment. Further, clutch size, hatching success, brood size, and fledging success were not significantly affected by experimental treatment. Invertebrate abundance and richness were similar between years, across grass heights, as well as across nest box trails. Invertebrate abundance and richness were not correlated with any of the nesting success metrics and did not statistically influence nesting success. Experimental manipulation of supplemental feeding did not appear to influence nesting success of Eastern Bluebirds. Supplemental food availability may only have significant effects on nest success in years with low environmental food availability. Although we did not find direct benefits of supplemental feeding for bluebirds, bird feeding can be beneficial to the community, professional scientists and wildlife in general through engagement of the public in science and conservation.