It looks like Pretty Boy may be having a reaction to something causing the redness. External parasites such as mites, excessive itching, and rubbing on cage bars may all cause redness or loss of feathers. Infections from bacteria or fungus may also cause feather loss and redness. It is best to have the area looked at by your vet, who can recommend treatment such as a mite medication or antifungal to help the area clear up. It can take some time for the feathers to regrow, so even after treatment it may take a little time for the area to return to normal.