From the Ears of Whales – Part I

 

w3Ahab pursued one in Moby Dick. The biblical Jonah was swallowed by one. As children we were awed by Geppetto being swallowed by one.  Nowadays, millions of people hop on a boat or gather on shore just to see one. Indeed, whales, those mammoth sea creatures that roam the ocean deep from the tip of South Africa to the edges ow7f the Arctic, continue to capture our imagination and fill us with awe.  In Europe, North America, South Africa, Hawaii, and elsewhere around the world, whale watching is a favorite sport   Seeing the tail or the breaking of water by a whale is a spectacular sight.

Many whales are very acrobatic, even breaching (jumping) high out of the water and then slapping the water as they come back down – the splash can be heard for up to a kilometer. Sometimes whales twirl around while breaching. Breaching may be done purely for play, though it may also be used to loosen skin parasites, to express some social meaning, or to communicate with other whales.   Most species of whales are known to breach at times. Humpback whales are especially acrobatic and known for their energetic breaching, as are gray whales and right whales. Humpbacks breach more frequently when the seas are rough (and their normal vocalizations are less likely to be hw2eard over the roar of the seas). This suggests that the noise of breaching may be used as a signal

Our knowledge of these creatures has increased substantially since thwe days of Moby Dick, Jonah and the fairy tales of Pinocchio.  There are about 86 species of whales, dolphins and porpoises in the Order Cetacea, which is further divided into two sub-orders, the Odontocetes, or toothed whales, and the Mysticetes, or baleen whales. Cetaceans can differ greatly in their appearance, distribution, behavior and, to some degree in their hearing according to the species.

Whales inhabit all of the world’s major oceans, from the Arctic and Antarctic Oceans to the tropical waters in and w1around the center of the equator.  Depending on species and migration patterns, some whales are particularly abundant in some locations while completely absent from others.  Factors such as food supply, the whale’s overall size (which affects the climate the whale can comfortably survive in), and mating grounds may also affect the location of a particular species of whale.  For example, killer whales (actually, part of the dolphin family) can be found in all of the major oceans, but are more concerned with migrating to where their food supply goes than where they mate. Therefore their prey plays a large role in where the killer whale lives.  Humpback whales, on the other hand, travel thousands of miles from the colder polar regions they inhabit to warmer tropical climates during migration periods to find a mate and bear offspring.

How do Whales Hear?

Whales hear a bit w4differently from other mammals, and their sense of hearing has evolved over millions of years to enable them to hear in water as opposed to hearing through the air.   Newly described fossils, with tiny ear bones intact, reveal for the first time how the ancestors of whales and dolphins developed their finely tuned underwater hearing.

Hearing is the most important sense in modern whales.  Toothed whales, such as dolphins, rely on their auditory sense when hunting prey by echolocation.  The whale ear, initially designed for hearing in air, became adapted for hearing underwater in less than ten million years of evolution. Fossil studies suggest that w5evolution of underwater hearing in cetaceans, focused on changes in sound transmission mechanisms.

While sounds travel farther and faster underwater, hearing in the marine environment presents a different set of challenges from hearing on land.   On land, sound vibrations strike the mammalian eardrum through an air-filled, outer ear canal. But when a typical land mammal is submerged, water filw6ls that ear canal, diminishing the ability of the eardrum to transmit sound.  An additional challenge to underwater hearing is distortion: sound easily transfers from water through an animal’s body, arriving at the ears via the bone and tissue of the head.  As a result, sound strikes both ears simultaneously, making it impossible to detect the sound’s direction of origin.  Whales also have specialized soft tissue sound conduction paths with a 50% greater octave spans than most land mammals, and two to three-fold the auditory neural densities of any other known mammal.  Current anatomical data show that whale ears are predominantly ultrasonic adapted and should therefore have relatively poor sensitivities to lower frequencies; some species, such as beaked whales, have unusually well-developed vestibular structures which may anomalously enhance beaked whale sensitivities to intense, low frequency sounds.  The auditory map (above) for whales is interesting in that they are most sensitive to signals around 40,000 Hz. While this map is interesting only about 13% of the whale species have really been studied for hearing.  Some speculation is that many of whales can tell the differences in areas of the world by the differences in ocean waters and how they conduct sound.

Now what can we learn from the ears of whales? 

You will be surprised! 

Next week’s

Hearing International looks at what the ears of whales tell scientists about the changes in the world.

About Robert Traynor

Robert M. Traynor, Ed.D., MBA is the CEO and practicing audiologist at Audiology Associates, Inc., in Greeley, Colorado with particular emphasis in amplification and operative monitoring, offering all general audiological services to patients of all ages. Dr. Traynor holds degrees from the University of Northern Colorado (BA, 1972, MA 1973, Ed.D., 1975), the University of Phoenix (MBA, 2006) as well as Post Doctoral Study at Northwestern University (1984). He taught Audiology at the University of Northern Colorado (1973-1982), University of Arkansas for Medical Sciences (1976-77) and Colorado State University (1982-1993). Dr. Traynor is a retired Lt. Colonel from the US Army Reserve Medical Service Corps and currently serves as an Adjunct Professor of Audiology at the University of Florida, the University of Colorado, and the University of Northern Colorado. For 17 years he was Senior International Audiology Consultant to a major hearing instrument manufacturer traveling all over the world providing academic audiological and product orientation for distributors and staff. A clinician and practice manager for over 35 years, Dr. Traynor has lectured on most aspects of the field of Audiology in over 40 countries. Dr. Traynor is the current President of the Colorado Academy of Audiology and co-author of Strategic Practice Management a text used in most universities to train audiologists in practice management, now being updated to a 2nd edition.