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Tecumseh Fitch on vocal length & larynx size

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  • Marc Verhaegen
    Because the length of the vocal folds determines the lowest frequency at which the folds can vibrate, and long folds are thus able to produce lower
    Message 1 of 1 , Aug 1, 2010
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      Because the length of the vocal folds determines the lowest frequency at
      which the folds can vibrate, and long folds are thus able to produce lower
      frequencies, one might expect that a low fundamental would provide a
      reliable indication of large body size.
      This is indeed true if we look across a large range of spp (mice have high
      fundamentals relative to dogs, elephants very much lower), but the size of
      the larynx is not tightly constrained by body size. Thus, a huge larynx has
      independently evolved in many mammal spp, probably in response to selection
      for low-pitched voices, eg, in howler monkeys Alouatta, the larynx & hyoid
      have grown to fill the space between mandible & sternum, giving these small
      monkeys remarkably impressive low-pitched voices. The most extreme example
      is seen in the hammerhead bat Hypsignathus monstrosus, in which the larynx
      of males expands to fill the entire thoracic cavity, pushing the heart,
      lungs & trachea down into the abdomen.
      A similar though less impressive increase in larynx dimensions is observed
      in human males and is responsible for their voice change at puberty.
      Even without greatly enlarging the larynx, a transformation of the vocal
      folds into massive vocal pads in large cats & other mammals makes the
      production of very low-pitched roars possible in some large mammals.
      Not surprisingly, the lowest pitched voices are possessed by the largest
      animals, which can produce infra-sound. Because low frequencies can travel
      further than high frequencies in some environments, infrasonic vocalizations
      probably represent the most widely broadcast animal signals in existence.
      Elephants produce & hear extremely low frequency rumbles & other infrasonic
      vibrations. In certain environments (eg, open savannah with Tp inversions),
      such sounds are able to carry more than 10 km, leading to unusu.large
      vocally mediated communication networks in African elephants. But even these
      long-distance communication systems are dwarfed by those of the large baleen
      whales : both fin- & blue whale males Balaenoptera physalis & musculus
      produce low-frequency vocalizations with 20 Hz fundamental frequencies ;
      under ideal conditions a vocalization from a single animal can fill an
      entire ocean basin. The mechanism by which these low-frequency sounds are
      produced is unknown, but baleen whales possess a large larynx with a massive
      vocal fold & a laryngeal sac that allows air recirculation, making it
      possible that the aero-dynamic/myo-elastic theory applies even to these
      infrasonic vocalizations.
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