Directional sound transmission and reception of the beluga whale ( <i>Delphinapterus leucas</i> )

The biosonar system of odontocetes enables directional sound transmission and reception. Beluga whales (<i>Delphinapterus leucas</i>) are notable among odontocetes as they can alter the shape of their fatty melon during sound transmission, potentially suggesting distinct acoustic capabilities. In this study, we developed a biosonar model of a beluga whale using computed tomography scanning and structural reconstruction to examine directional transmission and reception in this species. This model could modulate sounds into a directional beam using either single or dual sources. Across frequencies from 5 to 60 kHz, the directivity indices for the left and right sound sources ranged from 4.83 to 15.2 dB and 4.81-14.7 dB, respectively. When both sound sources were used simultaneously, there was an average increase of at least 2.26 dB in energy and 0.68 dB in the directivity index compared to using a single source. Additionally, beam steering was achieved in the dual-source transmission by introducing a timing difference between the two sources. The simulations indicated that sound reception was frequency-dependent, with the greatest sensitivity to lateral sounds at low frequencies and to forward sounds at high frequencies. These results suggested that both transmission and reception in beluga whales were directional and frequency-dependent.