Why are some birds able to talk?

Songbirds and parrots are the two groups of birds who can learn and mimic by human speech. Pet birds can also be taught to speak by their owners by mimicking their voices. The young of some birds learn to communicate vocally by social learning, imitating their parents, as well as the dominate birds of their flock.

Birds can't talk. Unless, of course, you include chirping that sounds like certain words.