A Sonic Net reduces damage to sunflower by blackbirds (Icteridae): Implications for broad-scale agriculture and crop establishment

Blackbirds, such as red-winged blackbirds (Agelaius phoeniceus), are notorious agricultural pests and damage crops at multiple stages of growth. Our aim was to test a novel deterrent, the use of sound designed to mask communication among birds (termed a “Sonic Net”), to deter blackbirds (Icteridae) from target areas of maturing sunflower crops. The Sonic Net masks communication of a target species by delivering “pink noise” that overlaps with the frequencies that the species uses for acoustic communication. If birds cannot hear predators or conspecific warning calls their perceived predation risk increases, and they relocate to an area with lower predation risk. Working with local sunflower producers in North Dakota, USA we set up experimental sites in three sunflower fields that were actively used by mixed-species blackbird flocks. In each field, we established two 0.2 ha plots and measured the initial area of damage for 63 individually-marked sunflowers. We applied the Sonic Net treatment to one of the paired plots in each field. At the end of the 20-day treatment period, we measured the total area damaged on the individually-marked sunflowers from each plot to calculate the change in damage for each sunflower. In all three fields, Sonic Net treatments substantially reduced percent damage to sunflowers, by 28.6% (95% CI: 12.5–41.7%), 63.6% (57.2–69.0%) and 22.6% (16.6–28.1%) for fields in Burleigh, McIntosh, and Emmons, respectively. In addition, sunflowers with a higher initial area of available seed experienced higher damage. We predict that the effect of the Sonic Net treatment may be greater in other crop phases and types, such as in the establishment phase or ground cover crops. During crop establishment there is a relative lack of tall, three-dimensional vegetational structure, which would allow for more effective spread of the Sonic Net sound and offer fewer physical refugia for birds to lower their perceived predation risk. We suggest both larger scale agricultural tests of the Sonic Net and efficacy tests for protecting crops at early growth stages to further explore the usefulness of this technology for crop protection.