Ducks or Pigeons

This morning I looked out from my second floor bathroom window to the roof of the house next door.  And what did I see but Mr. and Mrs. Duck on the roof!

I ran downstairs to get my camera.  When I'd come back up, Mr Duck was standing and Mrs. Duck was still lying down.  She soon got up and they both flew off.

What are ducks doing on the roof of a three story building?!