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A combination of hereditary and environmental factors is believed to determine the sounds that birds are able to produce. A. Although only male chaffinches are able to sing in the wild, Thorpe found that he could teach hand-reared females to copy songs from recordings and live tutors. B. Chaffinches reared in isolation produce songs that differ significantly from those of normal birds, suggesting that some social influence is important for learning a song precisely. C. Birds vary a great deal with respect to both the variety of sounds they are able to learn and the conditions that must be present for them to be able to learn their species' song. D. Chaffinches that are exposed only to other bird species for the first few weeks of their life are likely to learn the songs of those species instead of the chaffinch song. E. Researchers believe that both the circuitry or a bird's brain and its interactions with other birds of the same species may prevent birds from learning the songs of other species. F. The ability of deaf birds to produce their normal species' song suggests that genes play a much greater role than environment in determining the behavior of most bird species.