Birds have been shown to provide effective pest removal services in many agricultural systems, but the majority of those studies have taken place in “wildlife friendly” or tropical agriculture where bird density and/or diversity tends to be high. Most agriculture in the US, however, consists of industrialized monocrop systems, which often do not harbor high bird diversity. Nevertheless, birds do make use of these fields, especially when they are adjacent to source habitat such as grasslands or prairies. While insectivorous and omnivorous birds may provide services by eating pest insects, they can provide disservices directly by eating or damaging crops, or indirectly by eating “beneficial” arthropods such as arthropod predators. Very few studies have examined whether birds provide net services or disservices in these industrialized monocrop systems. I conducted a series of experiments to quantify bird services and disservices in the two most commonly grown crops in the Midwest, corn and soybeans. I conducted these experiments on fields adjacent to prairies or grasslands. I used exclosures to examine the overall indirect effects of birds on crop damage and yield, and a fecal DNA diet analysis to characterize the arthropod prey of birds caught on or near the cropped fields.
Results/Conclusions
I found that birds provided significant pest control services in a corn field in 2016, but significant disservices in the adjacent soy field. In 2017, I found that birds again provided disservices in soy when measured by soybean leaf damage, but there was no resulting effect on crop yield. I also found that birds were consuming major corn pests, including Northern and Western corn rootworms (Diabrotica barberi and D. vergifera). The results of this research suggest that birds may have significant indirect effects even in industrial monocrop systems. Whether those indirect effects become services or disservices may depend on a variety of factors, including which pest species cause the most economic damage. Because the dominant crop pest species change over time, I suggest a need for further research on bird services and disservices on large-scale industrialized farms.