Knock, knock knocking on heaven's

 Actually,

 it was also knocking on my computer!

Ja, to remove the bugs.

So he asked me what I did - I answered "astronomy, and you?" 

" I am an ornithologist"

 

 

 Me: Oh, really? Knock, knock!
Ornithologist: Who’s there?
Me: Woodpeckers.
Ornithologist: Woodpeckers who?
Me: No, that’s the owl. And you call yourself an ornithologist?

 

 

Now whoo is a wise old bird?

 

 

WOB