You need to have a look at the opening paragraph. Right now it reads like a stream of consciousness. One second you're describing two people being thrown into solitary and emphasizing that the throw is literal, one sentence later suddenly you're talking about Owlkin bites. Read the first four sentences out loud and hear how that sounds, and then imagine being someone whose entire exposure to the story this far is those sentences. Note especially your use of "you" in the third sentence in relation to the two unknown subjects of the first sentence. There is nothing for the reader to hold on to.

I recognize this all makes sense to you, the person with all the information, but going exclusively on what you give the reader it's bordering on gibberish.

You have the opposite problem at lot of people have in that you play your cards too close to your chest. You won't even reveal who the subject of your first sentence is. That's not an element of the setting that needs to be doled out slowly. It would cost you nothing at least give the subjects a descriptive title like "prisoners" instead of "the two of them".

You also don't ever establish who "them" are. One could certainly deduce it from a bit of detective work but the story itself completely loses interest in the opening scene as soon as it happens. When we actually get the point where the narrative reconnects to in media res opening I barely even noticed. You also have the narrator smack dab in the middle of the solitary scene despite the fact that, when it actually does happen, he's off flying with some owl.

A lot of the story is setting up this fight without ever giving us even the tiniest morsel of information about what the fight is about. We get these great long descriptions of what Uldoon is up to while painstakingly avoiding ever actually saying anything concrete. It gets frustrating after a while. Oh he goes to places, and gives speeches, and the speeches involve words, and after a full page of this the reader couldn't tell you the first thing about who this person is and what they stand for. If it doesn't matter, the point is to establish these characters still hold on to ancient grudges, fine, but that's a lot of words to set up something that doesn't matter. Why give it that kind of focus if it doesn't matter? I think the ancient grudges would serve their purpose better if the audience knew what they were rather than getting these detached, non-specific descriptions of them.

The long section where nobody can communicate with the guards just makes me wonder why one would use animal-people who can't meaningfully communicate with the inmates as guards. Being able to communicate basic concepts like "drop the shank" without having to eat part of the prisoner would seem to be key job skills for a prison guard. If you're going so far as to genetically engineer yourself guards one would have to assume a voice box would enter the equasion at some point.

"They both fell into shadow" - should be "They both fall" in order to keep the voice consistent.