Adult Eastern Rosellas have a single post-breeding moult each year, from December to May. This moult is complete except in some bids, mostly females, that defer moult of outer primaries until the following year. Birds fledge in juvenile plumage, pass into pre-adult plumage when two to six months old with a moult of the head and body feathers and pass into adult plumage when twelve to eighteen months old with a complete moult. Replacement of primaries starts with middle primaries and progresses inwards and outwards from this focus. Average duration of primary moult is 114 days. A major difference between Eastern Rosellas and the taxonomically related Budgerigar Melopsittacus undulatus is that Eastern Rosellas moult regularly after breeding, while Budgerigars moult continuously, even when breeding. Budgerigars moult into pre-adult and adult plumages at a younger age than do Eastern Rosellas.