Why a duck?

"There's a duck in the back yard!" said Thomas, earlier today.  Well, duh! I thought, but no, he meant besides Pretzel and Zachary.  And indeed there was.  An actual mallard - smaller and prettier than either of ours, and presumably capable of flight, otherwise how did it get there?

He seemed a bit confused.  Maybe he saw the other ducks while passing and assumed this is where everyone was hanging out.  It's not even as if we have a pond at the moment, as we're draining it prior to re-structuring.  Clearly he got bored, though, because he's gone now.