Wildlife Society Bulletin (Dec 2024)
Effective range of auditory frightening devices based on hearing capabilities and antipredator responses of nuisance blackbirds
Abstract
Abstract A variety of acoustic strategies have been implemented to disperse wildlife from areas of human‐wildlife conflict. Propane cannons are a popular tool; however, their efficacy based on avian behavior has yet to be fully explored. We collected sound attenuation data for a propane cannon, compared to a rifle and shotgun, with reference to hearing capabilities in birds. We evaluated the behavioral responses of red‐winged blackbirds (Agelaius phoeniceus, RWBL) and brown‐headed cowbirds (Molothrus ater, BHCO) to detonations of a cannon. We placed birds in individual enclosures, void of visual stimuli, at 15–495 m from a cannon and evaluated responses (i.e., relaxed, vigilant, startled) to cannon blasts using 2 approaches: 1) incremental, where individual birds were exposed to a series of detonations at decreasing distances and 2) random assignment, where individual birds were randomly assigned distances and exposed to 2 series of 4 cannon blasts. We found behavioral responses of birds significantly decreased at greater distances (χ2(1) = 127, P < 0.001), regardless of species (χ2(1) = 0.74, P = 0.389), when incrementally approached. The probability of startling (i.e., flinch, wing flap, feather compression, or flight) was greater than vigilance (i.e., increased head turning, sudden head‐up, or neck extension) within 64 m for BHCO and 136 m for RWBL. We found a significant effect of distance (χ2(1) = 97.8, P < 0.001), between species (χ2(1) = 19.6, P < 0.001), and blast number (χ2(3) = 17.6, P < 0.001) when birds were randomly assigned a distance from the cannon. With the first cannon blast, the probability of startling was greater than vigilance or relaxed within 334 m for BHCO and 153 m for RWBL. With subsequent blasts the probability of startling was greater than vigilance and relaxed within 204–221 m of the cannon for BHCO, but startling was never greater than vigilance for RWBL. We note that the estimated range of the cannon is conservative given birds are contained with limited flight ability. Nevertheless, information on effective range and avian responses to repeated blasts informs managers on the potential interstimulus timing and distribution of propane cannons to protect resources from birds.
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