Social group signatures in hummingbird displays provide evidence of co-occurrence of vocal and visual learning

Vocal learning, in which animals modify their vocalizations based on social experience, has evolved in several lineages of mammals and birds, including humans. Despite much attention, the question of how this key cognitive trait has evolved remains unanswered. The motor theory for the origin of vocal learning posits that neural centers specialized for vocal learning arose from adjacent areas in the brain devoted to general motor learning. One prediction of this hypothesis is that visual displays that rely on complex motor patterns may also be learned in taxa with vocal learning. While learning of both spoken and gestural languages is well-documented in humans, the occurrence of learned visual displays has rarely been examined in non-human animals. We tested for geographic variation consistent with learning of visual displays in long-billed hermits (Phaethornis longirostris), a lek-mating hummingbird that, like humans, has both learned vocalizations and elaborate visual displays. We foun...