My dad owned a cockatiel a number of years ago and after some work it was very friendly, would come when called, perch on your hand/shoulder, and was generally a real pal. Then he made the mistake of taking in a second one and instantly the bird turned into a rotten *******. Completely antisocial with people.
I suspect many birds are this way. My Campbell's went from timid to virtually wild first week out of the brooder. Today their favorite game is "run away". They are enjoying their life in their new run by the stream with each other and are good about going in their box at night so as long as they give me eggs they can do what they like IMO. It's a shame since they're really a great looking bird, butt perhaps next year I'll grab half a dozen of another breed that's reported to be friendlier. Being able to lead them around the yard for bug hunting would be really sweet. My chickens are pretty good about following me and letting me pick them up, though not nearly as cool looking as the ducks.