This ALWAYS happens with owls...even if they are not starving. If there is one much older and one young enough, the small one will get eaten. It happens on almost every owl nest.
There’s no recusing it. That will only scare the mom off. Like the last person said, this happens a lot. When there are four owlets in a nest and food isn’t plentiful, being the fourth owlet is a death sentence for you. These babies are starving, would you really let that baby starve to death? What’s happening to that chick is basically mercy from a slow agonizing death that they’re all experiencing. It’s sad but it’s what happens in nature. When the other chicks die mom will feed them to the surviving chick, if there was one.