The Distinctive Forehead Cleft of the Risso’s Dolphin (Grampus griseus) Hardly Affects Biosonar Beam Formation
Journal
Animals
Journal Volume
12
Journal Issue
24
Date Issued
2022-12-01
Author(s)
Abstract
The Risso’s dolphin (Grampus griseus) has a distinctive vertical crease (or cleft) along the anterior surface of the forehead. Previous studies have speculated that the cleft may contribute to biosonar beam formation. To explore this, we constructed 2D finite element models based on computer tomography data of the head of a naturally deceased Risso’s dolphin. The simulated acoustic near-field signals, far-field signals, and transmission beam patterns were compared to corresponding measurements from a live, echolocating Risso’s dolphin. To investigate the effect of the cleft, we filled the cleft with neighboring soft tissues in our model, creating a hypothetical “cleftless” forehead, as found in other odontocetes. We compared the acoustic pressure field and the beam pattern between the clefted and cleftless cases. Our results suggest that the cleft plays an insignificant role in forehead biosonar sound propagation and far-field beam formation. Furthermore, the cleft was not responsible for the bimodal click spectrum recorded and reported from this species.
Subjects
biosonar beam formation; CT scan; echolocation; finite element model; forehead cleft; Risso’s dolphin
Type
journal article