Morton, Eugene S., and Jake Page
Eugene S. Morton: Ornithologist and researcher in animal vocalization and the evolutionary relationships of birds and plants at the Smithsonian Institution and adjunct professor at the University of Maryland teaching graduate and postdoctoral students courses in animal behavior and ecology.

Jake Page: Former editor of Natural History and science editor of Smithsonian. The author of more than a dozen books and many natural history articles and essays in a variety of periodicals.

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. . . with few exceptions, the vocalizations of animals&endash;the songs and calls of birds, the grunts and roars and purrs of animals, the croaks of toads and frogs, the cricket's chirp, the astonishing array of underwater clicks and booms emitted by fish&endash;all these sounds evolved for purposes that had nothing to do with mankind. Animal Talk, 1992

What we think of as intellect has to have a biological function or it wouldn't have come into existence at all. Ibid.

In the tropics, bird song tends to be fairly constant throughout the year, unlike in the temperate north. Ibid.

The mockingbird also draws attention . . . to the fact that some singing birds learn new songs or variations of songs throughout life . . . Ibid.

A tilled field full of soft, furrowed earth has a profoundly different effect on sound traveling over it than, say, an asphalt parking lot. Ibid.