Birds Online
  Home > Health and diseases > Plumage defects > French moult (Polyoma virus)
  Normal French Molt/BFDThe French moult is a disease that occurs in budgies and some other pet bird species. First symptoms can typically be observed when the birds are still very young. At first, the chicks seem to develop in a normal way. But then the  fledglings (young birds) whose plumage is nearly full-grown suddenly lose all their secondary and tail feathers - these are the longest feathers. In most cases this happens when the birds are about six to eight weeks old. Some birds lose all these large feathers, others are lucky and only lose a a few large feathers. Usually, the small feathers that are covering a bird's of the body, e.g. the belly, are not affected by the disease. In some cases, however, abnormalities of the body plumage is known. Nearly all birds suffering from the French moult are not able to fly for the rest of their lives because their wing feathers which provide the ability to fly either never grow back or - if they do - grow with abnormalities. Most affected birds are able to run very fast, others just hop around.

Plumage defects due to French moult
Plumage defects caused by the French moult

What causes the disease and how is it transmitted?
It's the so-called Polyoma virus that causes the French Molt and another form of the disease called BFD = Budgerigar Fledgling Disease. BFD is often deadly for the affected young birds while the French moult "only" causes disabilities due to the plumage defects.

Until today the way of infection with these viruses it is not known in all its details. Some experts claim that transmission takes place in the nest; the virus is transmitted from the parents to the eggs. Thus, it would be no good idea to knowingly let budgies who suffer from the French moult have chicks! The risk of a new generation of infected birds is too high.

Another big problem is that in some cases adult birds carry the virus without showing symptoms of the disease. They can transmit the pathogenic germ to their chicks and the disease seems to occur out of nowhere. Therefore bird owners who would like to breed should keep this potential danger in mind and let their birds undergo a test that can tell whether they are infected or not.

Can older birds transmit the disease to other adult birds?
Pucki suffers from BFDThe danger to be infected as an adult bird is still discussed by researchers. Some scientists believe infected birds can transmit the disease and healthy, adult con-specifics can become ill as well. In many cases, these adult birds won't lose their plumage but they are "reservoirs" of the viruses for the rest of their lives. As soon as they are breeding, the circle closes and their offspring will most probably suffer from the French moult or BFD - at least in theory. But there are other avian vets who refuse this hypothesis. On their opinion there is no transmission of the virus in adult birds. If this would be true, only young birds would be in danger.

Unfortunately there are no final evidences for both theories. As a bird owner you have to consider properly whether to adopt an infected bird and let it become a member your flock or not. If the first hypothesis would be correct, the complete flock could be infected and therefore would be unsuitable for further breeding.

I'm not able and willing to give a recommendation for keeping infected birds in a "normal" flock at this place. Every bird owner has to decide for herself (or himself) how important ethical aspects are and if she (or he) has any breeding attempts.

Is there any cure?
Until today, no therapy that could heal the French moult is known. Affected birds whose feathers are brittle and weak can be supported by special food supplements and by silica. By adding silica and/or food supplements to a bird's food, you can support the feather growth efficiently. Please discuss the dosage with your avian vet.

Typical symptoms of the French moult in budgies
Harmless French MoltThe French moult doesn't always look the same. There are several typical courses of the disease. Comparatively harmless was the course of disease in Tethys' case, she was one of my birds. The photo on the right shows that only some tail and primary feathers were missing, thus she could hardly fly. Tethys wasn't able to lift herself into the air when she was flapping with her wings. But if I set her to a higher place in the bird room and later she wanted to go back to her favourite branch which as placed on the floor, she spread her wings and fluttered down slowly. She didn't fall down like a stone because with the few secondary feathers that were left, she was able to decrease speed and land softly.

Typical symptoms of the French moult in an adult budgieThe typical symptoms of this disease in an adult budgie who became infected as a chick is shown in the photo on the right. All large feathers on the wings (the primaries) and the tail feathers are missing. The remaining feathers are often broken due to mechanical stress. The reason for this is that the birds often try to fly and then stumble to the ground. You have to make sure that affected birds can't climb up too high because if they would fall, severe injuries like broken bones could occur.

Extreme French MoltIn the rare case of an extreme French moult, birds not only lack the large feathers. They also lose their small feathers and some birds become more or less naked. Medea who lives in my bird flock is shown in the photo on the right. She suffered from an extreme course of the French moult. Her entire body showed patches of bare skin and she of course wasn't able to fly. In winter she loved to perch on a branch which was placed on the floor of my bird room right in front of the heater. People who care for birds like her should provide a room temperature of at least 20 degrees Celsius. Else the birds would feel cold because of the lack of feathers and they are in danger of becoming ill due to the low temperature. They should be brought out of the room while the window is open in winter.

Extreme French MoltThe photo on the right shows the male budgie Fröschlein (this is German and means "little frog") who also suffered from a very extreme form of the French moult. This handicapped bird lived in a large cage together with his beloved fellow called Flöhchen. Their keeper made the cage safe for them because birds without feathers can hurt their skin when they fall off their perches. Therefore the cage floor had been padded to avoid any injury. Please note that the severe form of the French moult is very rare and that most birds who look like Medea or Fröschlein do not suffer from this disease but from PBFD. This disease is even more grave and therefore birds who show patches of naked skin should be tested for Polyoma virus and PBFD. It is impossible to tell the symptoms of these diseases apart by just having a look at a bird.

All photos and the text on this page are protected by the copyright law. In case you'd like to use photos or texts for your own non-commercial purpose, please contact the author.