Frequency sensitivity in Northern saw-whet owls (Aegolius acadicus)

• Published in: Journal of Comparative Physiology Vol. 204; no. 2; pp. 145 - 154
• Main Authors: Beatini, Julia R., Proudfoot, Glenn A., Gall, Megan D.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-02-2018; Springer Nature B.V
• Subjects: Aegolius acadicus; Animal Physiology; Biomedical and Life Sciences; Bird migration; Brain stem; Frequency dependence; Life Sciences; Neurosciences; Original Paper; Owls; Phylogeny; Prey; Sensitivity; Sensitivity analysis; Species; Thresholds; Zoology; Hearing; Peripheral auditory processing; Northern saw-whet owl; Communication
• ISSN: 0340-7594; 1432-1351
• DOI: 10.1007/s00359-017-1216-2

Northern saw-whet owls (
Aegolius acadicus
) are known for their unique asymmetrical ear structure and ability to localize prey acoustically, yet few attempts have been made to explore the auditory capabilities of this species. In this study, we evoked auditory brainstem responses (ABRs) with tonebursts to assess three main hypotheses regarding the evolution of auditory sensitivity: sender-receiver matching, ecological constraints, and phylogenetic/morphological constraints. We found that ABR amplitude increased with increasing stimulus level, which is consistent with results in other avian species. ABR amplitudes, latencies, and thresholds indicate that the hearing range of Northern saw-whet owls extends from 0.7 to 8.6 kHz, with an extended frequency range of best sensitivity between 1.6 and 7.1 kHz. Sensitivity fell off rapidly above and below these frequencies. The average audiogram was structurally similar to those found in other species of owls, suggesting that phylogeny or morphology may be constraining the frequency range of auditory sensitivity. However, ABR thresholds were 10–25 dB lower than those of Eastern screech-owls (
Megascops asio
), with thresholds below 0 dB SPL in some individuals. The lowest thresholds were at frequencies not found in the vocalizations of Northern saw-whet owls, suggesting ecological constraints rather than conspecific vocalizations are driving absolute sensitivity.