Budgie very quiet, fluffed and lethargic, but eats a lot
Our budgie - which is between 7 or 8 years old - has been very off in his behavior for the last two to three months. Normally he is very chatty and sociable and would come out to visit with the family early in the morning before work and in the evening as we settled in after dinner.
Sometime in October or November (approximately three months ago) his behavior started to change. At first we noticed that he spent a lot of the day sleeping, or at least resting with his head tucked under his wing; this was new behavior, but we though it might just be because he was getting older.
Then he stopped coming out of his cage much. Previously he would come out of his cage to fly around and visit, or just to scamper around on his cage, at least a dozen times a day. Now if he comes out once or twice it's an unusual event.
Then we noticed that our usually chatty budgie, who had quite a wide vocabulary, had stopped making much noise at all. He'll still occasionally chatter or burble, but he almost never talks.
When he's not sleeping, he spends most of his time hunched up and fluffy near the back of his cage. His droppings are runny and green. What's odd is that he hasn't lost his appetite. The time I see him most active is when I go to feed him. He descends on his seed dish like a starving man. He spends much more time eating now than he did prior to becoming ill; and not just his seed. Any food we give him -- millet, molting conditioner, his cuttlebone -- he gobbles like mad. He also drinks more water now than he used to.
We've taken him to the avian vet twice. They took blood and found nothing wrong. Then they took x-rays and found nothing wrong. At his initial visit, when they took blood, they found that he was a little dehydrated and had slightly elevated uric acid, but nothing extreme. He'd also lost a little weight since his last checkup earlier in the year. He's clearly not a well budgie, but they don't know what is causing it.
Since he clearly still has an appetite I keep wondering if it's something missing from his diet, but I don't know what it could be. Despite his appetite, he's always been a picky eater. He won't eat anything sticky, like fruit, or leafy, like lettuce. I've considered sneaking some egg food into his seed to give him some more protein, but I'm scared he'll notice it and stop eating entirely rather than eat something he doesn't want.
I hope you can help!