Re. dead bird, I don't think that's it...
Think it was more that Creeky had seen the dead bird under the attic window sill, which is where it should have been, which lead him
away from solving it earlier. It was only when he saw the gardener dealing with another dead bird (who commented that they were very frequent) that he realised the bird under the attic sill could well have been coincidence.
It was entertaining enough, three annoying things though:
1) Well, not so annoying, but... did anyone else think it was majorly boob-centric, or is it just my mind?!

Seemed like there was some kind of cleavage shot every 2 minutes. But I didn't appreciate the whole 3D porn thing - JC has always been reliable family viewing, why they had to introduce something you're going to be uncomfortable watching with your grandparents puzzles me.
2) Usually with Jonathan Creek there is one big mystery (often "the mechanics"), then a few little social or sub-mystery mysteries. I thought these were particularly cr@p in this episode. Once the secret of the room has been revealed, the stuff about the throat-slitting was an anti-climax (i.e. it actually happened, as observed) and the stuff about the newspaper was just boring.
3) And finally, what was the painting about? After all those dramatic shots, it's just a personal symbol of a wrongful decision?! Come on!