I've finally made it back to my yellow birds today, and had quite a productive morning.
I grew my last sun block until it fitted with its fellows.
then I added them all onto the big piece I'd already done.
Then, for the umpteenth time I laid out my remaining yellow birds, changed my mind twice and ended up with the chunk that is now in the bottom right corner. All I need to do now is attach the top bird and then this side can be added on.
The remaining birds are not so much a well thought out set as the ones I haven't wanted anywhere else, so I'm hoping that they will not take this amiss and that I can piece them together without too much difficulty. If that goes smoothly then I can think about what next.