He's lucky that pigeon isn't from Chelsea.

LOL, I love how he has to break character for a moment to laugh when he first sees the plastered pigeon.

That moment of genuine, uncontainable hilarity makes this for me.

It's a terrible David Attenborough accent, but when he first sees the pigeon is genuinely hilarious.

I imagined him rehearsing this little intro over and over again as quickly as he could before the bird might have woken up, and then filming and finally turning around to see the pigeon, confirming that, yes, it's still passed out in the exact same spot.
That nailed me in the funnies too.

Yeah, I'm fairly sure he saw the pigeon before, like @artician says, just that he was overly amused by the fact the bird was still there. Even practiced comedians sometimes have problems delivering a line, let alone somebody who likely was making things up on the spot. I imagine it as him seeing the pigeon and after confirming it was alive, and seeing the apples, made something up on the spot and delivered it as best as he could. I'd probably have assumed it was dead rather than drunk.