Understanding spatiotemporal effects of food supplementation on host-parasite interactions using community-based science

Abstract

Supplemental feeding can increase the overall health of animals but also can have variable effects on animals dealing with parasites. Furthermore, the spatial and temporal effects of food supplementation on host-parasite interactions remain poorly understood, likely because large-scale, coordinated efforts are difficult. Here, we introduce the Nest Parasite Community Science Project (hereafter “Project”), which is a community-based science project that coordinates studies with bird nest box “landlords” from the public and scientific community. The Project was established to understand broad ecological patterns between box-nesting birds and their nest parasite community. The goal of this study was to use data collected by the Project to determine the effect of food supplementation on Eastern Bluebirds (Sialia sialis) and their nest parasite community across the geographic range of the bluebirds from 2018-2020. Nest box landlords either fed their bluebirds mealworms or not, then followed the nesting success of the birds (number of eggs, percent hatched, percent fledged). Nests were sent to our lab where we identified and quantified all nest parasite taxa. Birds from the western range laid more eggs than the eastern range, but this spatial effect was not observed for hatching success. However, food supplementation increased hatching success across years and the study area. We primarily found parasitic blow flies and fleas in the nests, which were restricted to northern latitudes. Within this geographic area, food supplementation affected blow fly abundance, but this effect varied across years, with abundances increasing, decreasing, or not changing, depending on the year. Interestingly, more landlords at southern latitudes fed bluebirds compared to northern latitudes, which contradicted the results of other community-based science projects. Our study demonstrates the importance of coordinated studies across years and locations to understand the effects of environmental heterogeneity on host-parasite dynamics.