Avian Ecosystem Services and Disservices Within a Mixed Landscape of Intensive Agriculture and Grassland

Much of the Midwest region of the United States is farmed intensively for corn and soybeans. Grasslands and prairies, once abundant in this landscape, are now found in small patches embedded within the agricultural matrix. These grasslands provide habitat for populations of birds, which forage both in natural and nearby cultivated habitats. Birds provide ecosystem services in this system by consuming herbivorous pest arthropods, or disservices by consuming beneficial predatory arthropods that would otherwise consume pests. I conducted a series of experimental and observational studies to examine the pest control services and disservices provided by birds within this study system. First, I conducted exclosure experiments using cages to exclude birds from corn and soybean crops adjacent to a prairie. I found that birds provided significant net services in corn, but significant net disserves in the adjacent soybean crops. The next year, I again conducted exclosure experiments in soybeans, and measured the effect of birds on both leaf damage by pests and soybean grain yield. I found that exclosure plots had lower levels of leaf damage by pests than control plots, but there was no resulting effect on crop yield. I also found that sites with higher bird species richness had lower levels of leaf damage by pests. Finally, I further examined the diets of grassland/soybean field bird communities via DNA barcoding. I compared the diets of different bird species and birds captured at different sites. I found that the bird community consumed a wide variety of prey species, and that diets differed by both bird species and capture site. I also found that birds consumed more herbivorous than predatory arthropods. My findings suggest that birds responded opportunistically to prey availability, and are likely able to respond quickly to pest outbreaks. The combined results of this dissertation suggest that birds have the potential to provide surprisingly large economic effects within an intensively farmed corn and soybean landscape. Grassland and prairie habitat near farmland provides a source population of birds that provide these top-down trophic interactions. Furthermore, birds provide services beyond those provided by beneficial arthropod natural enemies, while disservices are limited.