Cross-posting from the other thread on same topic....
Start from the cage, not away from the cage. I learned that same advice 16 years ago. Now? I believe it's just bad advice!
I also don't believe that a bird *needs* to be clipped in order to tame them.
Millet or other favorite treats can go a long way into earning their trust!
Most birds are probably cage aggressive because they don't have good experience with hands around their cages. It's not because they are trying to be "dominant", or they're being "territorial" over their cage (which that can indeed happen!). A lot of birds also find safety in their cage, so if they feel the need to go back to their cage, let them. This tells them that it's ok to be with you if you wont hold them back. You just need to convince them that spending time with you is a reward in itself. If the bird is happy being on you when you stand next to the cage (and the bird is not being restricted from going back to their cage), that's a great sign!
If they still feel the need to be at their cage, that's ok, too! Don't force him away from the cage if you don't have to. Make it his choice to leave his cage, but make it rewarding! This will create a stronger bond and trust between you and him.
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Keep training sessions short! It's better to do multiple 30 second to 5 minute training sessions a day rather than 30-60 minute training sessions once or twice a day! When I was feeding my budgies by hand, it was maybe 15 minutes max once a day, every day. I wasn't trying to train any specific behaviors though, such as step up. Nor was I actually trying to "tame" them, in the sense that most people use. It was merely a social interaction and trust forming type of 'training'.
I also don't believe that the birds need to be separated in order to tame them. Monkey see, monkey do. If one bird watches the interaction of another with a human, it's possible to tame two (or more) birds together. Because I was working with 5 adult, flighted budgies, I ended up working with 5 adult cockatiels, most flighted. At least two were ex-breeders, too! One probably parent raised, the others hand raised and then ignored and neglected or unknown. If I kept this behavior up with my current cockatiels, I could probably earn the trust of a wild caught african ringneck as well! When I fed the cockatiels by hand, she showed interest. She would fly over, scaring the cockatiels off, but then once the cockatiels were gone, she would lose what confidence she had and would fly off herself.
The first cockatiel was Sunshine. Her previous owner had bred her parents then hand raised her and kept her as one of their pets. Only, he was a kid that grew up and "forgot" about her and her family. After watching me feed the budgies by hand, she decided she wanted that same interaction with me, and ended up following me around the room waiting to be fed. It took me two weeks to figure out what it was that she wanted!!!
The next cockatiel, following Sunshine's lead, is Faye. Although I don't know Faye's full history, I'm sure she was hand raised and loved at some point in time, but ended up becoming neglected and passed around from home to home. She's been in at least 3 homes prior to mine and the last one was pretty horrible! You can see in the first video how hesitant and unsure she is. Likewise, behind and below her, there's food. She doesn't *have* to eat from my hands, but she's choosing to!
Which leads to the next video, where you can see her behavior is completely different than the first video! Also, I'm feeding her pellets by hand instead of seeds!
Which leads to the third video... (ignore the third cockatiel, Casey! she climbed up my arm!) This video shows Pistachio (plucked head 'tiel), Sunshine's father. He used to be a *very* skittish bird, to the point that I couldn't get anywhere close to him without him freaking out. He's still a skittish bird, but not like he used to be. In fact, if I offer food or treats by hand, he's either the first or second cockatiel to come to me! The other cockatiel, Tomi Girl (looks like a healthy male but it is fact a female!) is another cockatiel from a bad home as well.
Taming a bird doesn't have to be that difficult, and it certainly doesn't need to take more than a few minutes a day! The main goal should be to keep *every* interaction with a bird a positive one! If the bird is avoiding you, "growling" or "hissing" at you, possibly even biting you, then it's not a positive experience for the bird. If this is happening, then you need to reevaluate your training techniques and try to figure out how to go at the bird's pace, so it can be a great experience for both of you!