When did scientists first identify bird vocal learning?

Researchers in the 20th century showed that many birds, especially songbirds, learn their vocalizations rather than producing them purely by instinct. This was a major discovery because it linked bird song to learning, memory, and brain development. Studies in the 1950s and later helped establish birds as important models for studying vocal learning. The findings also influenced neuroscience by showing that complex learned communication is not unique to humans.