Chemical Repellents for Reducing Blackbird Damage on Mature Sunflowers: The Importance of Plant Structure and Avian Behavior in Field Applications

Abstract

Across North America, blackbirds (Icteridae) depredate high-energy crops, such as sunflower (Helianthus annuus), placing an economic burden on producers. Chemically-defended crops, in the form of human-applied repellents, may induce birds to forage elsewhere if a learned aversion can be established. However, repellent deployment must be feasible for producers at the scale of commercial agriculture. Thus, my main objective was to evaluate the efficacy of anthraquinone-based repellents applied to ripening sunflower for reducing blackbird damage. I conducted concentration response (no-choice) and preference tests (two-choice) to evaluate repellent efficacy on captive blackbirds using application strategies practical for agricultural producers. I evaluated field application strategies to assess the potential for broad-scale application using new drop-nozzle technology. Additionally, I describe behavior of captive blackbirds as they interact with ripening sunflower to further inform repellent application. Our results support the conclusion that application of anthraquinone-based repellents is not currently a feasible option for ripening sunflower.