There's a little round robin
and a little round wren
the wren is rounder than the robin
but the robin's redder than the wren
some say the robin is a sweeter tweeter
but the wren's the doyen of song
she's a round yo-yo of feathers
she's a little bomb of sound
You can see I've been messing around with little alterations. It's sound and rhythm I'm trying to get right - well, not 'right' but pleasing to my ear, at least.
I'd like an extra syllable in the first 2 lines. And I'm not sure about yo-yo. Our wren hops up and down a lot but perhaps not qute like a yo-yo. A yo-yo has the roundness I want, that's why it occurred to me. Sometimes you end up compromising...