I literally saw a swan do exactly that to a seagull.
Had a loaf of bread, was tossing pieces to a pair of swans just paddling their way through, only as soon as a piece would hit the water, a seagull would seemingly materialise out of hyperspace like Right There and swallow it before the swans could even react. I could tell one swan was getting particularly annoyed.
I tossed a nice big piece practically right in front of Pist-Off Swan, a seagull swooped in and grabbed and swallowed it, and next thing I see, the swan grabs the seagull’s whole head in his beak, and literally pulls the seagull out of the water and flings him a dozen feet away.
I’m standing there with my mouth hanging open, like, “Did I just see that??”, and a nearby seagull is now getting a staredown by Pist-Off Swan, and I could almost hear the “gulp!” as POS is giving him this Chung Li type “You are next!” look.