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7 hypothesis for reduced predation rates in flocks relates to HARASSMENT, REPELLENT, AND DETERRENT increased vigilance for predator detection. Flock members TECHNIQUES can warn other birds of the presence of the predator using alarm calls or visual cues (Charnov and Krebs 1975). Harassment, repellents, and deterrents encompass a wide range of techniques and methods used to manipulate behavior We use an example to place the aforementioned ecological of birds to shift use away from an area or resource (Werner and concepts and flocking behavior into an airport management Clark 2003). The use of a method or device must be coupled context. Merlins may use airport properties as a consequence with an understanding the mode of behavior response; simply of songbirds foraging in grasslands. These songbirds may pre- stated, the tool must of match the task, as shown in Figure 3. fer to forage in taller grass because of more abundant prey; Essentially, two types of repellents exist--primary and sec- thus under ideal free distribution we would expect higher ondary (Clark 1998). Primary repellents cause involuntary abundance of songbirds in tall grass areas. Mowing areas of withdrawal or escape behavior in an animal usually through high grass closer to runways for aircraft safety would leave taste, odor, or irritation (Clark 1998). Secondary repellents fewer areas of tall grass, further concentrating songbirds. induce an undesirable physiological effect for the animal, These flocks may reduce foraging efficiency for merlins, thus such as gastric malaise. The goal of airport biologists is to reducing overall merlin use of airports and associated risk to create avoidance behavior such that the animal will discon- aircraft. However, the larger flocks of songbirds would pose a tinue occupying an area or to reduce ease of foraging for food greater risk to aircraft. As individual songbirds pose little risk in a given patch (Werner and Clark 2003). The periodicity of to aircraft, management actions would not likely be directed repellents is also an important determinant of their effective- toward these individuals. However, larger flocks of these ness. Devices used to repel, haze, and generally frighten ani- birds may well trigger implementation of control measures. mals can be periodic, random, or motion activated (Gilsdorf As Figure 2 shows, understanding ecological relationships et al. 2002). The timing of the stimuli has a direct impact within and between species, and how these species interact on effectiveness. Random or animal-activated devices may with their environment, is critical for maximizing efficiency reduce habituation and increase the time of protection over and effectiveness of control measures. nonrandom (i.e., systematic) devices (Koehler et al. 1990). FIGURE 2 Integrated pest management (Source : Werner and Clark 2003).