OMG, I’m so sorry about Riley! That’s how our sweet Mae went, too, though we knew she had a tumor and she was being treated. I hope your vet can do a necropsy, though at that age it may not be a question that needs answering. I’m so sorry for your loss and how traumatic it is to feel so helpless as a bird passes right before your eyes. You gave him a great life. Glad he was so content.