If I were an evil emperor in a fantasy world, I would have a an enormous aviary full of exotic birds that are exceptionally well cared for. They would be from a distant enough land that there would be very few people in my kingdom that knew much about them, they would be a friendly but not overly territorial species, and moderately intelligent. Like puffins. They would not, crucially, be able to imitate sounds and 'speak', but they would be very trainable and curious. Occasionally importing new birds for my aviary would be the Big Frivolous Indulgence that my political enemies make fun of.
I will also have a sorceror in my employ. When a hero or a renegade or a political rival is in a situation where I can safely kill them, they will instead be turned into a bird and added to my aviary. I would not brag about this; it would be a complete secret, known only to me and my sorceror. In situations where I capture multiple people working together, only one would go in the aviary;the others can be imprisoned or killed or whatever. If they escape and I reacquire them later, another one can go in the aviary. The point here is that nobody going in the aviary can safely assume that another bird in there is their teammate.
Because I would be trickling real birds in there, too. And I would train some of them to do 'intelligent' things like tap out prime numbers or scratch shapes into the dirt with their beaks. I would train some of them to pick at the locks and bars as if they were trying to escape. I would not train them all the same way, or train many of them at all.
Sometimes, a new bird goes into the aviary -- fellow revolutionary? Or just a bird? Is it trying to communicate to you that it's human, or just being friendly and imitating you because that's what smart friendly birds do? People would develop opinions and theories over time. They'd amass in a group of the smartest ones, pretty sure that they're closest four or five friends are humans, are using their invented little language of wing-flaps and trills with a human mind behind it... but can they ever really be sure?
Most people, when going into the aviary, would assume that all of the birds are captured enemies. So why are some of them hard to have ongoing communication with, to learn about, to plan with? Are these the natural communication barriers of someone in a bird body, or does being a bird make them stupider over time? Will that happen to them also?
Sometimes, if I capture a pair, I'll imprison them separately, then turn one into a bird and put them in the aviary at the same time as a real bird that's trained to have a couple of their partner's mannerisms.
When I interact with the birds, even in private, I won't secretly mock them or make clever veiled references to their past or act at all like I remember that they were once human. They are my birds, that I imported at great expense. And I've brought a treat for them; some fresh fruit, and another friend to share it with! A new bird!
