The Diverse Sensory Specializations of Cetacea

Abstract

Cetaceans (whales, including dolphins and porpoises) have many unique sensory adaptations that enable them to perceive and respond to stimuli underwater. These adaptations include audition, vocalization, vision, balance, chemoreception, and somatosensation.Cetaceans generate and receive sounds at both ends of the frequency spectrum, and use these sounds for both communication and echolocation. Toothed whales (odontocetes) specialize in high frequency sounds, while baleen whales (mysticetes) focus on low frequency sounds. High frequencies have short wavelengths, and thus enable odontocetes to detect minute features in the reflected echoes related to geometry, texture, density, vector, velocity, etc. Nasal structures generate two different frequencies simultaneously (stereo echolocation). Sounds are received in jaw fats and transmitted to the ears. These features help odontocetes target and catch prey, but can also be used for short‐range navigation and communication.The mysticete larynx generates low frequency sounds. Echoes from these large wavelengths can reveal large features at a distance, facilitating navigation through the ocean landscape during migration. As low frequencies also attenuate more slowly, they can be used for long distance communication. Low frequencies present a hearing dilemma, as wavelengths can be larger than the whale! However, using the large skull as an antenna allows mysticetes to perceive change along most of the wavelength, and relay that information through bony conduction to the ear. Males use highly patterned vocalizations (songs) that advertise sexuality. Songs can be shared with and repeated by new whale groups, thus indicating sophisticated cultural exchange.Vision is another sense that is adapted to life underwater. Cetacean eyes allow visual acuity both above and below water. These include changes to the lens and retina that accommodate light filtering at various depths, and differences in the refraction of light in water versus air. The sclera is also thickened, and may be an adaptation that prevents the eye from deforming under high pressures during diving.Much less is known about the senses of touch, balance, smell, or taste. Cetacean skin is very sensitive, but little is known about its specific somatosensory detection abilities (vibration, water flow, pressure, electromagnetic fields, etc.). Balance seems essential for navigating in three‐dimensional space, yet paradoxically, cetacean semicircular canals are reduced. Smell and taste appear useless to a predator that feeds underwater and swallows prey whole, yet olfactory bulbs and taste buds appear to persist at least in baleen whales. These unique features present open areas of inquiry in cetacean sensory ecology.