Communication & Echolocation
Sound in the Sea
- Sound waves travel through water at a speed of about 1.5 km/sec
(0.9 mi/sec), which is four-and-a-half times as fast as sound traveling through air.
- Killer whales probably rely on sound production and reception to navigate, communicate, and hunt in dark or murky waters. Under these conditions, sight is of little use.
- Killer whales produce sounds for two overlapping functions: communicating and echolocating.
- Killer whales produce whistles, echolocation clicks, pulsed calls, low-frequency pops, and jaw claps.
- Killer whales produce clicks and sounds that resemble moans, trills, grunts, whistles, squeaks, and creaking doors. They make these sounds at any time and at all depths. The sounds vary in volume, wavelength, and pattern.
- A killer whale makes sounds by moving air between nasal sacs in the blowhole region.
- In contrast, a human makes sound by forcing air through the larynx. The vocal cords in the larynx vibrate as air flows across them, producing sounds. Our throat, tongue, mouth and lips shape these sounds into speech. The larynx of a killer whale does not have vocal cords.
- A tissue complex in a toothed whale's nasal region, called the dorsal bursa, is the site of sound production. This complex includes "phonic lips" (sometimes called "monkey lips")—structures that project into the nasal passage. Toothed whales make at least some sounds by forcing air through the nasal passage and past the phonic lips: the surrounding tissue vibrates, producing sound.
- During some vocalizations, killer whales actually release air from the blowhole, but these bubble trails and clouds are probably a visual display. Releasing air isn't required for sound production.
- A killer whale can produce sound from at least two separate sources in its complex of nasal sacs.
- The frequency of killer whale whistles ranges from about 0.5 to 40 kHz, with peak energy at 6 to 12 kHz. Studying northern resident killer whales, researchers found that the whales produced more whistles when they were close to other individuals and only sporadically emitted them when the whales were dispersed over larger areas.
- Pulsed calls are the most common vocalization of killer whales.
- Experts think these calls function in group recognition and coordination of behavior.
- Killer whales make these calls at frequencies of about 0.5 to 25 kHz, with peak energy at 1 to 6 kHz.
- Calls that sound the same time after time are called stereotyped calls. All a killer whale's stereotyped calls make up that whale's repertoire.
- The individuals of any particular pod share the same repertoire of calls, a vocalization system called a dialect.
- Although scientists have noted that there is some type of structure to the calls, a dialect is not the same thing as a language.
- Analysis of killer whale call patterns has demonstrated substantial differences between the dialects of different pods.
- Pods that associate with one another may share certain calls ("clans").
- No two pods share the entire repertoire. Thus, each pod has its own unique dialect. In fact, the vocal repertoires of each pod remain distinct enough that scientists can identify pods by the sounds they make.
- Killer whales that are separated by great geographical distances have completely different dialects. An analysis of Icelandic and Norwegian killer whale pods revealed that the Icelandic population made 24 different calls and the Norwegian whales made 23 different calls, but the two populations did not share any of the same calls.
- A calf is most likely to develop calls like those of its mother. Vocal development studies at SeaWorld have determined that a calf learns its repertoire of calls selectively from its mother, even when other killer whales may be present and vocalize more frequently than the mother.
- A calf can vocalize within days of birth, but sound production is shaped with age. A calf's first vocalizations are "screams"-loud, high-pitched calls that bear no resemblance to adult-type calls.
- At about two months, a calf produces its first pulsed calls with similarities to adult-type calls.
- Vocal behavior appears not to be genetically predetermined. Calves learn which calls to make and under what circumstances.
- From two to six months, a calf's repertoire increases. Calves continue to learn calls until puberty.
- Like many other animals, toothed whales may also communicate using a variety of postures and gestures. Some behaviors, such as head-butting and jaw-snapping, are usually assumed to communicate aggression. The purpose of other behaviors, including breaching and pec-slapping, is not clearly understood.
- Bioacoustic studies can be an important means of tracking pod movements. If they provide a reliable index of genetic variability, they can also become a useful management tool.
- The term echolocation refers to an ability that odontocetes (and some other marine mammals and most bats) possess that enables them to locate and discriminate objects by projecting high-frequency sound waves and listening for echoes.
- A killer whale echolocates by producing clicks and then receiving and interpreting the resulting echo.
- The echolocating killer whale produces directional, broadband clicks in rapid succession, called a train. Each click lasts less than one millisecond. Killer whale echolocation clicks can be up to about 35 kHz, with their peak energy at about 12 to 25 kHz.
- The click trains pass through the melon (the rounded region of a killer whale's forehead), which consists of lipids (fats). The melon acts as an acoustical lens to focus these sound waves into a beam, which is projected forward into water in front of the whale.
- The sound waves produced by a killer whale bounce off objects in the water, and their echoes return to the killer whale.
- Echoes are probably received and conducted through the lower jaw to the ear. See Senses.
- An echolocating killer whale can determine the size, shape, speed, distance, direction, and even some of the internal structure of objects in the water.
Killer whales echolocate by producing high frequency clicks that pass
through the melon, then receiving and interpreting the resulting echo.
Relationship to Feeding Habits
- In the eastern North Pacific Ocean, resident whales vocalize more and echolocate more than transient whales, and they have a wider sound repertoire.
- Transient killer whales, which prey on marine mammals, probably rely more on passive listening than on echolocation to help them find prey.
- Scientists theorize that these differences in sound production are related to the whales' feeding habits. Transient killer whales, which prey mainly on marine mammals, keep quiet to avoid detection. The excellent hearing of a marine mammal might alert it to an echolocating or vocalizing killer whale, giving it the opportunity to flee.