The gorilla baby, Koko, was even better at using sign language. Today, as an adult, Koko is still learning. The learning of songbirds has been studied in the laboratory, as well as in the wild. Amazingly enough, canaries were found to grow entirely new brain cells, every year, during their molt. While molting male canaries sing very quietly, new glial cells are forming, which migrate to the learning centers of the brain.
Canaries can learn new songs by hearing tapes during the molt.
I've talked with some song canary breeders who were unaware of this change in the brain, yet have told me that this explained to them why some of their champions had poor songs the next season. The birds had forgotten what they'd learned. This research has important medical applications. When a mammal has a head injury, it can't regrow new brain cells. If we can learn what makes canary brain cells grow, maybe we can regenerate human cells as well.