Why has it been thought that the tropical regions are deficient in birds of song?

Because, from the abundance of the piece tribe, such as parrots, and some others of harsh note, it is probable that their sounds, in the tropical woods, often overpower and confound the more soft and sweet modulations of the warbler tribe. Still, it is a very unfounded notion that in the New World the brilliant hues of the birds take the place of the power of song. On the contrary, it would appear, from Wilson's American Ornithology, that the American song-birds are infinitely more numerous than those of Europe, and many of them superior to our most celebrated songsters.