HOW WHALES FEEL?
HOW WHALES FEEL?
Some of the senses that we and other terrestrial mammals
take for granted are either reduced or absent in cetaceans or fail to function
well in water. For example, it appears from their brain structure that toothed
species are unable to smell. Baleen species, on the other hand, appear to have
some related brain structures but it is not known whether these are functional.
It has been speculated that, as the blowholes evolved and migrated to the top
of the head, the neural pathways serving sense of smell may have been nearly
all sacrificed. Similarly, although at least some cetaceans have taste buds, the
nerves serving these have degenerated or are rudimentary.
The sense of touch has sometimes been described as weak too,
but this view is probably mistaken. Trainers of captive dolphins and small
whales often remark on their animals’ responsiveness to being touched or
rubbed, and both captive and freeranging cetacean individuals of all species
(particularly adults and calves, or members of the same subgroup) appear to
make frequent contact. This contact may help to maintain order within a group,
and stroking or touching are part of the courtship ritual in most species. The
area around the blowhole is also particularly sensitive and captive animals
often object strongly to being touched .
The sense of vision is developed to different degrees in
different species. Baleen species studied at close quarters underwater –
specifically a grey whale calf in captivity for a year, and free-ranging right
whales and humpback whales studied and filmed off Argentina and Hawaii – have
obviously tracked objects with vision underwater, and they can apparently see
moderately well both in water and in air. However, the position of the eyes so
restricts the field of vision in baleen whales that they probably do not have
stereoscopic vision.
On the other hand, the position of the eyes in most dolphins
and porpoises suggests that they have stereoscopic vision forward and downward.
Eye position in freshwater dolphins, which often swim on their side or upside
down while feeding, suggests that what vision they have is stereoscopic forward
and upward. By comparison, the bottlenose dolphin has extremely keen vision in
water. Judging from the way it watches and tracks airborne flying fish, it can
apparently see fairly well through the air–water interface as well. And
although preliminary experimental evidence suggests that their in-air vision is
poor, the accuracy with which dolphins leap high to take small fish out of a
trainer’s hand provides anecdotal evidence to the contrary.
Such variation can no doubt be explained with reference to
the habitats in which individual species have developed. For example, vision is
obviously more useful to species inhabiting clear open waters than to those
living in turbid rivers and flooded plains. The South American boutu and Chinese
beiji, for instance, appear to have very limited vision, and the Indian susus
are blind, their eyes reduced to slits that probably allow them to sense only
the direction 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 are
more than compensated for by cetaceans’ well-developed acoustic sense. Most
species are highly vocal, although they vary in the range of sounds they
produce, and many forage for food using echolocation1. Large baleen whales
primarily use the lower frequencies and are often limited in their repertoire.
Notable exceptions are the nearly song-like choruses of bowhead whales in
summer 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 (though the sperm whale apparently
produces a monotonous series of high-energy clicks and little else). Some of
the more complicated sounds are clearly communicative, although what role they
may play in the social life and ‘culture’ of cetaceans has been more the
subject of wild speculation than of solid science.
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