雅思阅读中的那些鲸鱼

 雅思阅读中的那些鲸鱼

  Sperm whale skeleton.Richard Lydekker,1894.

  The whale ear has specific adaptations to the marine environment.In humans,the middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance.In whales,and other marine mammals,there is no great difference between the outer and inner environments.Instead of sound passing through the outer ear to the middle ear,whales receive sound through the throat,from which it passes through a low-impedance fat-filled cavity to the inner ear.[41]The whale ear is acoustically isolated from the skull by air-filled sinus pockets,which allow for greater directional hearing underwater.[42]Odontocetes send out high frequency clicks from an organ known as a melon.This melon consists of fat,and the skull of any such creature containing a melon will have a large depression.The melon size varies between species,the bigger the more dependent they are of it.A beaked whale for example has a small bulge sitting on top of its skull,whereas a sperm whale's head is filled up mainly with the melon.[43][44][45][46]

  The whale eye is relatively small for its size,yet they do retain a good degree of eyesight.As well as this,the eyes of a whale are placed on the sides of its head,so their vision consists of two fields,rather than a binocular view like humans have.When belugas surface,their lens and cornea correct the nearsightedness that results from the refraction of light;they contain both rod and cone cells,meaning they can see in both dim and bright light,but they have far more rod cells than they do cone cells.Whales do,however,lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals.[47]Most whales have slightly flattened eyeballs,enlarged pupils(which shrink as they surface to prevent damage),slightly flattened corneas and a tapetum lucidum;these adaptations allow for large amounts of light to pass through the eye and,therefore,a very clear image of the surrounding area.In water,a whale can see around 10.7 metres(35 ft)ahead of itself,[citation needed][need quotation to verify]but,of course,they have a smaller range above water.They also have glands on the eyelids and outer corneal layer that act as protection for the cornea.[48][49]

  The olfactory lobes are absent in toothed whales,suggesting that they have no sense of smell.Some whales,such as the bowhead whale,possess a vomeronasal organ,which does mean that they can"sniff out"krill.[50]

  Whales are not thought to have a good sense of taste,as their taste buds are atrophied or missing altogether.However,some toothed whales have preferences between different kinds of fish,indicating some sort of attachment to taste.The presence of the Jacobson's organ indicates that whales can smell food once inside their mouth,which might be similar to the sensation of taste.[51]

  Communication

  Whale vocalization is likely to serve several purposes.Some species,such as the humpback whale,communicate using melodic sounds,known as whale song.These sounds may be extremely loud,depending on the species.Humpback whales only have been heard making clicks,while toothed whales use sonar that may generate up to 20,000 watts of sound(+73 dBm or+43 dBw)[52]and be heard for many miles.

  Captive whales have occasionally been known to mimic human speech.Scientists have suggested this indicates a strong desire on behalf of the whales to communicate with humans,as whales have a very different vocal mechanism,so imitating human speech likely takes considerable effort.[53]

  Whales emit two distinct kinds of acoustic signals,which are called whistles and clicks:[54]Clicks are quick broadband burst pulses,used for sonar,although some lower-frequency broadband vocalizations may serve a non-echolocative purpose such as communication;for example,the pulsed calls of belugas.Pulses in a click train are emitted at intervals of~35–50 milliseconds,and in general these inter-click intervals are slightly greater than the round-trip time of sound to the target.Whistles are narrow-band frequency modulated(FM)signals,used for communicative purposes,such as contact calls.

  Intelligence

  Whales are known to teach,learn,cooperate,scheme,and grieve.[55]The neocortex of many species of whale is home to elongated spindle neurons that,prior to 2007,were known only in hominids.[56]In humans,these cells are involved in social conduct,emotions,judgement,and theory of mind.Whale spindle neurons are found in areas of the brain that are homologous to where they are found in humans,suggesting that they perform a similar function.[57]

  雅思阅读中的那些鲸鱼

  Bubble net feeding

  Brain size was previously considered a major indicator of the intelligence of an animal.Since most of the brain is used for maintaining bodily functions,greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks.Allometric analysis indicates that mammalian brain size scales at approximately the?or?exponent of the body mass.Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalisation quotient that can be used as another indication of animal intelligence.Sperm whales have the largest brain mass of any animal on earth,averaging 8,000 cubic centimetres(490 in3)and 7.8 kilograms(17 lb)in mature males,in comparison to the average human brain which averages 1,450 cubic centimetres(88 in3)in mature males.[58]The brain to body mass ratio in some odontocetes,such as belugas and narwhals,is second only to humans.[59]

  Small whales are known to engage in complex play behaviour,which includes such things as producing stable underwater toroidal air-core vortex rings or"bubble rings".There are two main methods of bubble ring production:rapid puffing of a burst of air into the water and allowing it to rise to the surface,forming a ring,or swimming repeatedly in a circle and then stopping to inject air into the helical vortex currents thus formed.They also appear to enjoy biting the vortex-rings,so that they burst into many separate bubbles and then rise quickly to the surface.[60]Some believe this is a means of communication.[61]Whales are also known to produce bubble-nets for the purpose of foraging.[62]

  雅思阅读中的那些鲸鱼

  A southern right whale sailing

  Larger whales are also thought,to some degree,to engage in play.The southern right whale,for example,elevates their tail fluke above the water,remaining in the same position for a considerable amount of time.This is known as"sailing".It appears to be a form of play and is most commonly seen off the coast of Argentina and South Africa.Humpback whales,among others,are also known to display this behaviour.[63]