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1.5.12Why Do Birds Sing? Sexual Selection in Birds and Other Animals
Darwin noted (correctly) that in many species of birds and mammals, males vocalize (“sing”) and females don’t—or not nearly as much. Moreover, male vocalization occurs mainly in breeding season. The best singers have the best mating success. This is a form of sexual selection. The same sexual selective pressure gave rise to the capacity for music in humans.
There are more than 9,000 species of birds, of which about 4,000 sing. In birds, songs evolved to attract mates or to repel rivals for mates. Sexual selection in birds results in females choosing males with the most elaborate and varied repertoires of songs. Once the female and male have set up house, the male stops singing (sadly). Unless, for some reason, the male loses his mate. Then he goes nuts with singing again (hurrah!).
Male humpback whales sing competitively to attract females. Humpback whales even seem to improvise, like jazz musicians. They sing extended pieces lasting up to half an hour, anytime female humpbacks are in the neighbourhood—not only during mating season.
To be a sexually selected adaptation, music would have to confer reproductive benefits. According to the sexual selection hypothesis, music arose as a courtship display, evident in birdsong, for example. Most animals only ever produce calls during breeding season: birds, frogs, toads, insects, and many other species. And it’s almost always males vocalizing to attract females.