Plumage Problems

Parrots as a group are most susceptible feather complaints, and French molt has been a serious problem for Budgerigar breeders for over a century. It typically affects young birds as they leave the nest.
The flight and tail feathers are more fragile than normal, and break off, impairing the bird's ability to fly. Not all chicks in a nest will be affected, but the disease sometimes reaches epidemic proportions.

Viral Diseases

It is now clear that French molt caused by a virus, but its effects may be influenced by other factors, such as nutrition. The virus is present in the nest, presumably being excreted in the droppings or from the feathers, so you should take particular care when cleaning an affected nestbox. Use a separate brush, and avoid mixing these chicks with healthy ones in a temporary container. Such birds are best sold as pets, rather than being kept to form part of a breeding program.
Routine disinfection in the bird room will help to overcome this disease, as will an ioniser. There have been reports of a similar problem being encountered in other species, notably in Peach-faces. Lovebirds and Ring-necked Parakeets, but it does not seem widespread at present. Psittacine beak and feather disease is undoubtedly the most serious viral disease identified in recent years. From its origins in cockatoos, it has been confirmed in at least 36 different species. Efforts are being made to market a means of testing affected birds, and ultimately to produce a vaccine. At present,however, affected birds pose a serious risk to others. The virus is present in their droppings, feather dust, and crop, which suggests that chicks can acquire the infection.
"French Molt : This feather disease, caused by a virus, affects Budgerigars and other species, and other species, and results in stunted plumage. "