Behavioral response of reindeer (Rangifer tarandus) to acoustic stimuli

Abstract: Scare systems based on acoustic stimuli have been tested on several ungulates in recent years. The aim has been to investigate whether the method can be useful in situations where the animals must quickly be displaced from a specific site, for example, to prevent wildlife accidents. The method is based on inducing so-called anti-predator behaviors (flight and vigilance) by simulating predator presence via acoustic stimuli. However, there is a lack of research on how reindeer respond behaviorally to different acoustic stimuli, something that could be a useful method to keep animals away from critical infrastructure in the future. Therefore, the aim of this study was to investigate how reindeer react behaviorally to four acoustic stimuli: a predator (bear), white noise impulses (a wheezing sound), human voices, and sirens. A silent control was also included in the experiment to ensure that the reindeer were not disturbed by the equipment used for data collection. The experiment was conducted at three Sámi reindeer herding communities winter pastures in northern Sweden, with total seven study sites. The main questions before the study were: (1) How does the behavior change in reindeer when exposed to different acoustic stimuli? (2) What proportion of the observed reindeer react with a flight response as a result of being exposed to the different sounds? (3) Is there an appreciable difference between the four acoustic stimuli tested in the experiment when considering the two aforementioned questions? In the results of this study, reindeer reacted most strongly to sounds from predator and the white noise impulses. The change in behavior was evident as the animals shifted from predominantly foraging before the sound started to predominantly running when the sound was played. A similar trend was observed when comparing the flight response to the different sounds. The flight response differed significantly between stimuli, 92.0%, fled in response to predator stimuli, followed by noise impulses at 81.9%, human voices at 75.8%, and sirens at 46.5%. Reindeer never exhibited a flight response when exposed to the silent control. Furthermore, all evaluated acoustic stimuli resulted in a reduced foraging behavior compared to the silent control, where reindeer primarily foraged throughout the entire observation period. These findings indicate that sounds from predators (bear) and noise impulses elicited the most pronounced behavioral changes in reindeer during the study. Therefore, these sounds could be useful in the future for effectively removing and keeping reindeer at a distance, particularly in critical areas where preventing wildlife accidents is crucial.