Effects of a Combination of Auditory and Visual Stimuli on Crow Deterrence

Auditory stimuli, such as distress calls, are highly effective for controlling crows, but it has also been suggested that exposure to a single stimulus leads to habituation. In this study, we conducted an experiment on captive large-billed crows (Corvus macrorhynchos) to investigate the effects when a visual stimulus (a mirror) is added to the crow's distress call. Eight large-billed crows were divided into two groups; their foraging behaviours in the test cage were compared between a group only subjected to the auditory stimulus and a group subjected to both auditory and visual stimuli (combined stimuli). Both groups delayed the time to start feeding (i.e., latency time) compared with no stimulation (control condition). The group receiving only the auditory stimulus did not differ from the control condition in the number of landings on the food patch or total time spent at the food patch during the experiment. In contrast, when the combined stimuli were provided, the total time spent at the food patch during the experiment was less than in the control condition. This finding suggests that the combined stimuli were more effective at preventing the approach of crows and contributed to the long-term deterrence of crows compared with a single stimulus.