(Still, an uninspiring limerick, albeit an archetypical one of Lear’s.)

Thanks Hihoba for the elucidation of the function of “on vacation” in 12a; I’d assumed that NT was the enclitic form “-n’t” of “not” – but yours seems the better reading.

I really enjoyed this one, despite the howler at 42A, which I hadn’t even spotted as I solved the clue and read about only subsequent to solving on the Crossword Centre Message Board.

I saw E LEAR in the middle of the grid early on and guessed we were looking for some of his Nonsense Verse. Alas, there were a lot of unchecked letters in the top half of the grid in particular, which meant that, frustratingly, I just didn’t have enough letters in the grid to be able to identify the verse in question, despite knowing it, without a helping hand from Mr Google. For a long time, I had been barking up the wrong tree, having spotted the tawny o(wl) and so thinking that the reference must be to The Owl and the Pussycat.

I agree with you that the title was inspired, tying in as it did with the mournfulness and with the initial letters of the birds referred to in the limerick (?) – that was a quite inspired find on the part of Charybdis! I also very much liked the positioning of the nests in the grid to give the impression of the beard.

My only minor grumble is that the birds were a little bit on the obscure side, even for one with an ornithological bent – I’ve never come across horn owl for horned owl, not to mention the emu wren. However, they are all verifiable in Chambers, and, of course, I understand the constraints that the setter was working within to find birds with the right initial letters that could also be rearranged into the beard shape.