A review of the scientific evidence on the impact of biologically salient frightening devices to protect crops from avian pests

Abstract Many avian species are considered agricultural pests and cause severe and costly damage to crops worldwide. Crop producers use several methods to reduce damage by birds, with frightening devices serving among the most popular approaches. Biologically salient frightening devices, such as broadcast of conspecific alarm calls or placing predator models in fields, are considered particularly effective because they can trigger antipredator behaviors that reduce foraging activities or abundances of target birds locally. However, it remains unclear which type of biologically salient frightening device is most effective and whether some work best against certain bird species or on certain types of crops. We reviewed the published scientific literature to fill in these knowledge gaps about using biologically salient frightening devices for crop protection against avian pests. We found 48 experiments evaluating the impact(s) of biologically salient frightening devices. However, only 28 experiments statistically tested their results from which to draw conclusions. We found that alarm call playbacks, eye-spot balloons, or automated flying vehicles (UAVs) reduced avian abundance in all experiments. All experiments using alarm call playbacks, eye-spot balloons, hawk-kites, or UAVs effectively reduced crop damage. However, only experiments on passerine birds and in row crops were well-represented in these studies. We discuss potential biases in the literature that may limit our understanding of how birds respond to biologically salient frightening devices and suggest future directions that researchers might take to fill knowledge gaps.