Most of the inside of little birds is packed with their organs, leaving very little space for producing their loud songs. R. Haven Wiley discusses the mystery of how they manage to:
Although how it is accomplished is not yet completely understood, a male Hooded Warbler barely a half ounce (15 grams) in mass produces a song with an intensity of 80-90 decibels (in relation to the minimal intensity for human hearing) measured one meter from its bill. These intensities are typical for the long-distance songs of songbirds. The Screaming Piha of South American rainforests (a suboscine songbird) is one of the loudest birds in the world. Its vocalization, sounding something like a human “wolf whistle,” reaches 100 decibels (dB) one meter away. In contrast, normal human speech is only about 70 dB or less (100 times less power that 90 dB and 1,000 times less than 100 dB) and even an extremely loud shout by a human hardly reaches 90 dB. Yet humans have more than 1,000 times the overall mass (and presumable the muscle mass) of a warbler.
(Quoted from page 34 of Noise Matters: The Evolution of Communication, by R. Haven Wiley. Harvard University Press, 2015.)
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