Hearing abilities and sound reception of broadband

Authors: T Aran Mooney WeiCheng Yang HsinYi Yu Darlene R Ketten IFan Jen

Publish Date: 2015/04/30

Volume: 201, Issue: 8, Pages: 751-761

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Abstract

While odontocetes do not have an external pinna that guides sound to the middle ear they are considered to receive sound through specialized regions of the head and lower jaw Yet odontocetes differ in the shape of the lower jaw suggesting that hearing pathways may vary between species potentially influencing hearing directionality and noise impacts This work measured the audiogram and received sensitivity of a Risso’s dolphin Grampus griseus in an effort to comparatively examine how this species receives sound Jaw hearing thresholds were lowest most sensitive at two locations along the anterior midline region of the lower jaw the lower jaw tip and anterior part of the throat Responses were similarly low along a more posterior region of the lower mandible considered the area of best hearing in bottlenose dolphins Left and rightside differences were also noted suggesting possible left–right asymmetries in sound reception or differences in ear sensitivities The results indicate best hearing pathways may vary between the Risso’s dolphin and other odontocetes measured This animal received sound well supporting a proposed throat pathway For Risso’s dolphins in particular good ventral hearing would support their acoustic ecology by facilitating echodetection from their proposed downward oriented echolocation beamThe authors would like to express their gratitude to the administration training staff and veterinary group of the Farglory Ocean Park for their support of this project including providing animal access and care training schedule flexibility and assistance with data collection They also thank Dr Jiang Ping Wang and Dr Lien Siang Chou for their contributions during the planning stages and their assistance in Taiwan Various portions of this work were funded by a WHOI Interdisciplinary Award the Office of Naval Research and Farglory Ocean Park We thank them for their support This study was conducted with the approval of the Woods Hole Oceanographic Institution’s Animal Care and Utilization Committee protocol number DRK 3

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