French moult is the colloquial name for a condition that results in the loss of feathers in young budgerigars. Also known as budgerigar fledgling disease, French Moult can be caused by 2 different viruses: avian circovirus (also known as psittacine beak and feather disease) and avian polyomavirus. In this article we will address avian polyomavirus as that is the most common cause of French Moult in New Zealand and is usually what is meant when the term is used.

Polyomavirus is present in almost every budgerigar aviary in New Zealand due to the fact that it can lay dormant in otherwise healthy birds. Birds tend to shed the virus when they are experiencing stressors that can lower their immune system (such as breeding or being rehomed into a new aviary). If this happens during breeding, young birds with naïve and immature immune systems are exposed to these shedding birds and this is when we see the familiar loss of tail and flight feathers, and death in fledglings. The key to keeping it dormant and preventing it from spreading to birds, with a compromised or immature immune system, is in our management of our stock. In this article I will provide methods in preventing French Moult through animal management:

It takes about 4 months for an adult Budgie to contract polyomavirus, mount an immune response, and clear it. Thus one of the first things to do when getting in new birds is to quarantine them for 1-2 months. This is to ensure that the new bird is not carrying any disease that the stress of moving will bring out of dormancy. It also gives us time to treat the bird for illness and parasites before being introduced to our current flock, allowing us to extend our quarantine time if necessary.

Birds that are apparently healthy and have been through quarantine can then be introduced to the other birds. However, it is best not to breed from them for 16 weeks (4 months) minimum. This is so that if your current flock is carrying polyomavirus your new bird has time to contract it and get over it, or vice versa, thus they are less likely to shed during breeding. Most birds should have stopped shedding after 4 months, however they can shed the virus for up to 6 months .

This quarantine rule also applies to birds that have been shown. As bird shows are very common places for polyomavirus to spread.

Birds with missing feathers should not be bred as these birds are more likely to be continuously shedding the virus. It is best to wait for them to regrow the feathers before considering breeding them.

If possible fledglings should not be released into an aviary where new birds or affected birds are being housed. It is best to keep them separate until they are about 6 months old, whereby their immune systems are mature.

Breeding birds should be in top condition when entering the cages and free from parasites.

Provide good high energy foods during breeding, such as; pellets, a good quality seed mix, fruit and vegetables, soft foods, and appropriate supplements.

Do not exhaust your birds by allowing them to have too many clutches, eggs, or chicks in a season. A good rule would be 2 clutches of 4 chicks a season per pair.

Make sure to breed in a well-ventilated area and keep dust levels down. Vacuum cleaning is the most effective as it actively removes the dust without throwing it into the air.  Hygiene is important because polyomavirus is transmitted through feather dust and faecal matter.

Give birds a good break between seasons and allow them to recover properly. I like to breed my birds for one season a year which means a good 6 month break for them yearly.

These are the general rules that I follow in managing my flock. If you wish to read up further on the topic I recommend you read Dr Rob Marshall’s article on the disease, its cause, and its management after an outbreak.


Article with thanks, from: Taryn Hutt, BVSc




Schmidt, R. E. (2003) Pathology of pet and aviary birds Wiley-Blackwell

Thomas, D. (2007) Infectious diseases of wild birds John Wiley and Sons