It's sad to see your beautiful, colorful bird become raggedy-looking and naked. It's even harder when you don't quite know the cause. For many birds, excessive feather loss is not uncommon and unless the cause is found and tackled, the feathers may not return to their full glory. Here are some common reasons why your bird could be losing large chunks of feathers and what you can do about it.
This is fairly common in members of the parrot family. These birds require a large amount of stimulation, especially oral stimulation, to keep their minds occupied. Birds kept alone in cages for long periods with little to do may begin to chew or pull out their feathers for the simple need of social interaction and the need to chew or gnaw. Part of the problem is that once the bird gets into the habit of pulling out his feathers, it is very hard to get him to stop.
Social feather pulling:
Sometimes, birds aggressively pull out their mate's feathers, or groom them aggressively. This is common not only in caged birds, but poultry as well. With chickens, there's a tendency to peck at a wound and this may involve pulling out the surrounding feathers. In ducks, feather pulling during disagreements is not uncommon, especially pulling feathers around the tail area. Ducks may also pull head feathers during breeding season. Generally, the behavior is only temporary and works itself over time. However, if you find your bird is getting increasing bald, then you may want to separate the offending feather-puller.
Viruses and parasites:
Viruses can frequently cause a bird to lose all its feathers. This is what happened to Rhea, the lovebird, when a virus called Psittacine beak and feather disease attacked her. Unfortunately, as in the case of Rhea, sometimes the feathers don't grow back even when the bird gets better. Mites and other feather parasites may cause feathers to fall out, or the bird may scratch or pull the feathers out due to the irritation they can cause. Fortunately, though, in the case of parasites, getting rid of the bugs may allow the feathers to come back.
Another common reason for a bird becoming bald is a bad molt, but this is no cause of alarm as this can happen once in a while and they usually all grow back. As for the other three problems listed above, you may want to talk to your veterinarian about solutions to keep your bird from becoming completely bald and to rule out viruses and other medical reasons so the bird can be treated before every feather falls out.