His diet is not good. He needs access 24/7 to a nutritionally balanced feed. I use game bird maintenance for my birds (hens have oyster shell available 24/7 to supply the necessary additional calcium). I would also immediately add nutritional supplements to his water since he's struggling. It takes a bit of time to get these things to arrive by ordering on line so move fast if you can as he is in trouble and you may not have much time- Avia Charge 2000 is the one I use (google and it'll come up). Some folks use Rooster Booster.
While waiting for arrival of one of these, you can give him 3 drops Polyvisol liquid children's vitamins daily, administered via dropper gently along his beak line, so he swallows on his own and doesn't choke. The stuff tastes like crud so follow with some kind of tasty treat, e.g. cut up blueberries. If he is adverse to handling you may be able to get a poultry vitamin supplement at the feed store that can be used in drinking water till the more well rounded Avia arrives - I use Avia every single day in their water, at light iced tea color strength and my birds really look good. You can also get some baby parrot feeding formula to help build his strength.
As noted above, check him carefully for parasites. he may need to be wormed but I am concerned about doing this if he doesn't have worms as it is yet another stressor to their systems. However, if he has a heavy worm load, it would be essential (vets can test a stool sample if you want to check first).
The difficulty crowing is likely just a symptom of overall weakness. The sleeping, loss of feathers - all indicators that he is greatly compromised. So glad you posted - thank you - please hurry to get him what he needs so he can hopefully rebuild strength in time. To help cheer him while he's feeling so dreadful, see if you can get mealworms at a feed store or somewhere. He may also enjoy black oil sunflower seeds. But definitely right away get the nutritionally complete food too. Any feed store that tells you scratch is that food should be shut down - scratch is just a treat.
JJ
