Great find for this challenge, it DOES look like the duck (?) stepped back from the line. I am wishing for better clarity, though, this looks like a crop at the expense of loosing detail.
I'll be curious to see where this was taken. Black bellied whistleing ducks. I live in North Texas and it's very rare to see them there but we had some on our private lake last year. The are beautiful ducks. Very nice shot!
Wonderful sense of combat here. I don't think, however, that the negative space adds to the photo, rather the opposite: a close-up focusing on the expressions would have been more powerful.