Yes I think they know full well how hard they can bite if they want to. Mitzi sometimes goes through the motions of biting if I am doing something she doesn't want me to (such as spraying her) she doesn't really want to bite me but she lets me know that she could.
Somewhere in another universe, dear brother, you got saved.
If I am doing something Chy doesn't like, she warns me verbally. She says, "No, don't. Stop it. Go away". If I keep on, she will then say, "Ouch" meaning if I don't stop, I will be saying ouch. She is quite a character.
Max, CAG (In my heart forever) Taz, Tiel (Rest in peace my sweet girl) Chyloe, CAG
Ruby has done something similar to me when she is on the outside of her cage and I walk past. She'll give me a bite for no reason, but it's not hard. I hadn't thought of it as a "reminder" bite but could very well be. Also a reminder that this is her house and don't forget it - she is super protective of her cage!
Also would say that, over time, her "bites" are almost always of the reminder type. It's been a long time since either me or my g/f got really tagged. We've learned to read her body language and she has learned to control the strength of her beak, so it would seem!
You guys are so lucky, I really need to watch- Sid of course does it also once in a while if I walk too close to the cage and he is in a fun mood, but he does break the skin and bruises me. He does it in fun, but how do I get him to ease off a bit? He even laughs afterwards. Little stinker.