I'm an ornithologist and bird ringer and have a question about moulting, which I can't find any clear answer to elsewhere.
For those who are not familiar with the experession, moulting is the replacement of fur, skin, exoskeleton or, in a birds case, feathers.
Most birds moult all of their feathers once a year, and many species also have a second moult which in most cases is a partial one (replacement of body feathers and some wing coverts but not flight feathers). Feathers can also be shed/lost by accident, especially common is a release of some or all tail feathers when a bird is attacked by a predator. These feathers are then replaced immediately, but this is not defined as true moult.

For most species each moult (at least up to a certain age) results in a different plumage than the previous one - some changes are very obvious, like male mallards that switch from a somewhat extravagant drake plumage in the breeding season to a more female like, camouflaged plumage in summer/autumn, while other changes are more subtile, and only recognisable at close range, sometimes only in the hand.
For example, among passerines (sparrows, finches, warblers, tits, buntings etc.) one can usually tell adults apart from the birds born the same year by looking at the shape of the tail feathers. Adult tail feathers are generally more rounded and somewhat broader than the more pointy juvenile ones. However, if a juvenile looses a tail feather, then the next feather to grow out is of an adult shape, i.e. the feather that was due to develop and grow out first after next years breeding season.

My question:
All my litterature says that accidentally lost feathers are replaced immediatley, but is that really (and always) true regarding body feathers?

Will a lost body feather always be replaced immediately, and will the replacement feather be the "next in line feather", or will it be identical to the previous one? - Or, will lost body feathers not be replaced until regular moult?
In case of "next in line" development, then it should be theoretically possible to accelarate e.g. a herring gulls apparence to have adult plumage allready by it's first winter. (Herring gulls has many plumage stages, and adult plumage is first achived at the age of three.)

Furthermore: If a male mallard looses one of his drake plumage feathers by accident in winter/spring, will it be replaced by an eclipse feather (the next feather in line), by a new identical drake feather, or not replaced until the annual moult?
(I can't remember having seen a drake duck in early spring with admixed eclipse feathers, but I haven't really been looking for it either...)

By the way, any article about hormonal control regarding feather moult would be of great interest!

Regards from Norway

Bjørn Frostad

great questions but sadly I don't think we have an expert ornithologist who is on the site at the moment. what i can tell you (as an endocrinologist) having looked at the literature is that the hormonal control of moulting is VERY poorly studied and little of significance is know about it.