Now I need the bird species to be part of the story. Most songbirds are unable to learn new whistles. Corvids (crows, ravens, magpies, mockingbirds, cat birds, etc.) are a common family that is an exception, but generally they don't come to feeders. If it was a corvid, what was this guy putting in his feeder? Parrots are another major exception, and they will come to feeders, but they aren't native wildlife in many parts of the world. If it was a parrot, where did this guy live?