爱华网What Do Whales Feel? An examination ofthe functioning of the senses in cetaceans, the |
Some of thesenses that we and other terrestrial mammals take for granted areeither reduced or absent in cetaceans or fail to function well inwater. For example, it appears from their brain structure thattoothed species are unable to smell. Baleen species, on the otherhand, appear to have some related brain structures but it is notknown whether these are functional. It has been speculated that, asthe blowholes evolved and migrated to the top of the head, theneural pathways serving sense of smell may have been nearly allsacrificed. Similarly, although at least some cetaceans have tastebuds, the nerves serving these have degenerated or arerudimentary. The sense of touch has sometimes been described as weak too, butthis view is probably mistaken. Trainers of captive dolphins andsmall whales often remark on their animals’ responsiveness to beingtouched or rubbed, and both captive and freeranging cetaceanindividuals of all species (particularly adults and calves, ormembers of the same subgroup) appear to make frequent contact. Thiscontact may help to maintain order within a group, and stroking ortouching are part of the courtship ritual in most species. The areaaround the blowhole is also particularly sensitive and captiveanimals often object strongly to being touched there. The sense of vision is developed to different degrees in differentspecies. Baleen species studied at close quarters underwater –specifically a grey whale calf in captivity for a year, andfree-ranging right whales and humpback whales studied and filmedoff Argentina and Hawaii – have obviously tracked objects withvision underwater, and they can apparently see moderately well bothin water and in air. However, the position of the eyes so restrictsthe field of vision in baleen whales that they probably do not havestereoscopic vision. On the other hand, the position of the eyes in most dolphins andporpoises suggests that they have stereoscopic vision forward anddownward. Eye position in freshwater dolphins, which often swim ontheir side or upside down while feeding, suggests that what visionthey have is stereoscopic forward and upward. By comparison, thebottlenose dolphin has extremely keen vision in water. Judging fromthe way it watches and tracks airborne flying fish, it canapparently see fairly well through the air–water interface as well.And although preliminary experimental evidence suggests that theirin-air vision is poor, the accuracy with which dolphins leap highto take small fish out of a trainer’s hand provides anecdotalevidence to the contrary. Such variation can no doubt be explained with reference to thehabitats in which individual species have developed. For example,vision is obviously more useful to species inhabiting clear openwaters than to those living in turbid rivers and flooded plains.The South American boutu and Chinese beiji, for instance, appear tohave very limited vision, and the Indian susus are blind, theireyes reduced to slits that probably allow them to sense only thedirection and intensity of light. Although the senses of taste and smell appear to have deteriorated,and vision in water appears to be uncertain, such weaknesses aremore than compensated for by cetaceans’ well-developed acousticsense. Most species are highly vocal, although they vary in therange of sounds they produce, and many forage for food usingecholocation. Large baleen whales primarily use the lowerfrequencies and are often limited in their repertoire. Notableexceptions are the nearly song-like choruses of bowhead whales insummer and the complex, haunting utterances of the humpback whales.Toothed species in general employ more of the frequency spectrum,and produce a wider variety of sounds, than baleen species (thoughthe sperm whale apparently produces a monotonous series ofhigh-energy clicks and little else). Some of the more complicatedsounds are clearly communicative, although what role they may playin the social life and ‘culture’ of cetaceans has been more thesubject of wild speculation than of solid science. |
WhatDoWhalesFeel? what makes feel safe
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