I actually think you could genuinely just "float" the bird in the branchy block. No need to cache it and make it disappear. As long as it's a leaf block that has branches, just have the little guy literally float in it and do an animation (e.g. singing, resting, nesting etc?) in the block? Maybe even set up a system similar to bees when it comes to bird nests? If birds keep to one tree long enough, there will be a x chance for a birds nest to spawn? Or x chance that a tree may spawn with a nest. Containing eggs, extra twigs, grass etc. Some birds may attack you for messing with their nests.
Branchy Leaf/Leaf blocks are already somewhat transparent, so maybe it's a decent placeholder until further bird behaviors and tree/branch solutions are found? You could still have *most* of the bird watching experience hehe.
Genuinely, cannot wait for birds to be added. Going to add so much to the game
