 Consisting of chirps, squeaks, whistles and buzzes, hummingbird songs originate from at least seven specialized nuclei in the forebrain.In a genetic expression study, it was shown that these nuclei enable vocal learning (ability to acquire vocalizations through imitation), a rare trait known to occur in only two other groups of birds (parrots and songbirds) and a few groups of mammals (including humans, whales and dolphins and bats).Within the past 66 million years, only hummingbirds, parrots and songbirds out of 23 bird orders may have independently evolved seven similar forebrain structures for singing and vocal learning, indicating that evolution of these structures is under strong epigenetic constraints possibly derived from a common ancestor.