Update: We've had two showers together now. Yesterday I didn't expect him to want to be with me, but he wasn't content with being on the ledge of the shower. he drank a bit and got some water droplets on his chest. But this morning

he didn't even wait for a step up command and tried to fly straight to my shoulder, to which he promptly slipped, but is fine - and full on stood under the water for a good minuet or so, and leaning to get the water under his wings - and flapping them about when he was out of the water

I'm so proud! - of cause, he had plenty of options to move further up my arm if he didn't want to be under the water, and it was quickly apparent when hed had enough, so we got out then, but I'm so happy for him!! The only issue is the temp of the water - it was a bit warmer then warm, but not too hot. Is this a major issue, or should it be cool to mildly warm?
I also bought a harness for him yesterday, and he doesn't seem afraid of it at all, and wore the collar for a few seconds at a time with treats. I also got him a couple of forging toys, which i don't think hes had before. Its amazing, this feeling, knowing from his behavior that being with me has truely made his life better and more full with enrichment, even if i do make a couple of mistakes here and there.
I'm so happy
