Indeed, Rankinswood. I think the discussion is largely hypothetical; Smojo hasn't got his wood yet and is looking ahead, I'm currently plastered and doing very little for the next few weeks. I'd hope to be able to do brushcutting in a while, but am well aware of the birdies;
I should be able to use the brushcutter on the brambles and follow up by spot squirting any regrowth with SBK. (Got to consider nesting birdies though)
I'd guess most fledglings should have flown by now, seeing them in the garden and everything is earlier this year. That does raise the possibility though of them having a second brood, which could take us up to August.
Think the answer is care and observation before disturbing undergrowth at this time of year, or just leave till a bit later.