Assertion: hummingbird's trait | /r/AtLocation | only two other groups of birds
Facets:
Source sentences:
text: 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).