The site and physiologic mechanism(s) responsible for the generation of odontocete biosonar signals have eluded investigators for decades. To address these issues we subjected postmortem toothed whale heads to interrogation using medical imaging techniques. Most of the 40 specimens (from 19 species) were examined using x-ray computed tomography (CT) and/or magnetic resonance imaging (MR). Interpretation of scan images was aided by subsequent dissection of the specimens or, in one case, by cryosectioning. In all specimens we described a similar tissue complex and identified it as the hypothetical biosonar signal generator. This complex includes a small pair of fatty bursae embedded in a pair of connective tissue lips, a cartilaginous blade, a stout ligament, and an array of soft tissue air sacs. Comparing and contrasting the morphologic patterns of nasal structures across species representing every extant odontocete superfamily reveals probable homologous relationships, which suggests that all toothed whales may be making their biosonar signals by a similar mechanism.

Functional morphology and homology in the odontocete nasal complex: implications for sound generation

Recordings of underwater vocalizations and behavioural observations were collected from 16 photographically identified resident pods of killer whales (Orcinus orca) off Vancouver Island, British Columbia, during 1978–1983. Vocalizations recorded during 43 days spent with three representative pods were analyzed for each of five activity states: foraging, travelling, group-resting, socializing, and beach-rubbing. The whales produced three types of sounds that were assumed to be social signals: discrete calls, variable calls, and aberrant calls. Discrete calls dominated vocalization in most contexts. An increase in production of variable and aberrant calls was observed during socializing and beach-rubbing activities. Each resident pod had a group-specific repertoire of 7–17 discrete call types (mean = 10.7) that was consistent over a number of years. The relative use of different calls varied with activity, but no call type was correlated exclusively with any behaviour or circumstance that could be identifie...

Acoustic behaviour of resident killer whales (Orcinus orca) off Vancouver Island, British Columbia

https://www.econscience.org/val/pubs/orca_refs/barrett-lennard%2B96.pdf

The mixed blessing of echolocation: differences in sonar use by fish-eating and mammal-eating killer whales

About 70 million years ago, the terrestrial ancestors of whales and dolphins reentered the ocean where life originally began. Not only did this require dramatic shifts in locomotion for swimming and in respiration for diving, but the ocean also presented a very different sensory environment. The explosive way in which cetaceans breathe reduced the usefulness of olfaction, which has limited utility underwater. Light propagates great distances rapidly in air, which makes vision particularly useful for sensing distant objects on land or in air, but light does not propagate well in water. Few objects can be seen underwater at ranges of more than a few tens of meters. By contrast, sound travels particularly well underwater. The potential for the acoustic modality to sense distant sources of sound is highlighted by recent discoveries that we can detect low-frequency calls of whales at ranges of hundreds and sometimes thousands of kilometers (Costa 1993; Clark 1994b, 1995).

Communication and Acoustic Behavior of Dolphins and Whales

Killer whale (Orcinus orca) audiograms were measured using behavioral responses and auditory evoked potentials (AEPs) from two trained adult females. The mean auditory brainstem response (ABR) audiogram to tones between 1 and 100 kHz was 12 dB (re 1 μ Pa) less sensitive than behavioral audiograms from the same individuals (±8 dB). The ABR and behavioral audiogram curves had shapes that were generally consistent and had the best threshold agreement (5 dB) in the most sensitive range 18–42 kHz, and the least (22 dB) at higher frequencies 60–100 kHz. The most sensitive frequency in the mean Orcinus audiogram was 20 kHz (36 dB), a frequency lower than many other odontocetes, but one that matches peak spectral energy reported for wild killer whale echolocation clicks. A previously reported audiogram of a male Orcinus had greatest sensitivity in this range (15 kHz, ∼35 dB). Both whales reliably responded to 100-kHz tones (95 dB), and one whale to a 120-kHz tone, a variation from an earlier reported high-frequency limit of 32 kHz for a male Orcinus. Despite smaller amplitude ABRs than smaller delphinids, the results demonstrated that ABR audiometry can provide a useful suprathreshold estimate of hearing range in toothed whales.

Killer whale (Orcinus orca) hearing: auditory brainstem response and behavioral audiograms.

A new technique for recording dolphin echolocation signals during target‐discrimination tests is described. The technique utilizes sensors attached to the animal. A brief description of the sensors is provided. A short color film of dolphin echolocation tests performed using the attached sensors is shown. Problems in recording the transient‐like dolphin echolocation signals are discussed. A short summary of analyses of echolocation signals of two dolphins—an Atlantic bottlenose dolphin, Tursiops truncatus, Montagu, and an Amazon river dolphin, Inia geoffrensis—is presented. [This work was performed under contract with NURDC, San Diego, California.]

/pdf/recording-and-analysis-of-dolphin-echolocation-signals-p6ec65bnxl.pdf

Recording and Analysis of Dolphin Echolocation Signals

Problems in acquisition, storage, and analysis of delphinid echolocation signals are described and illustrated. It is shown that adequate bandwidth is the prime requisite for validity in measurement. However, idiosyncracies of the detector and recorder may alter the signal and, therefore, its derived characteristics. Uncertainty about the signal leads to ambiguous results in analysis.

R. T. Trochta

Papers

Recording and Analysis of Dolphin Echolocation Signals

Delphinid sonar: measurement and analysis