The crimson rosella (Platycercus elegans) is a parrot native to eastern and south eastern Australia which has been introduced to New Zealand and Norfolk Island. It is commonly found in, but not restricted to, mountain forests and gardens. The species as it now stands has subsumed two former separate species, the yellow rosella and the Adelaide rosella. Molecular studies show one of the three red-coloured races, var. nigrescens is genetically more distinct.
Platycercus elegans is a medium-sized Australian parrot at 36 cm (14 in) long, much of which is tail. There are seven subspecies, three of which are actually crimson. The red is replaced by yellow in the case of var. flaveolus and a mixture of red, orange and yellow in the Adelaide rosella. Adults and juveniles generally show strikingly different colouration in south-eastern populations, with predominantly greenish-olive body plumage on the juvenile, most persistent on the nape and breast. Juveniles are said to 'ripen' as they get older and turn from green to red. All races have blue cheeks and black-scalloped blue-margined wings and predominantly blue tail with predominantly red coloration. The crimson rosella’s blue tail feathers are one of the favourite decorations of the satin bowerbird. The bill is pale grey and the iris dark brown. There is very little sexual dimorphism in crimson rosellas. The most noticeable difference between genders is that males are up to 15% larger, and have a relatively larger and wider beak.
Nesting sites are hollows greater than 1 metre (3.3 feet) deep in tree trunks, limbs, and stumps. These may be up to 30 metres (98 feet) above the ground. The nesting site is selected by the female. Once the site is selected, the pair will prepare it by lining it with wood debris made from the hollow itself by gnawing and shredding it with their beaks. They do not bring in material from outside the hollow. Only one pair will nest in a particular tree. A pair will guard their nest by perching near it at chattering at other rosellas that approach. They will also guard a buffer zone of several trees radius around their nest, preventing other pairs from nesting in that area. The breeding season of the crimson rosella lasts from September through to February, and varies depending on the rainfall of each year; it starts earlier and lasts longer during wet years. The laying period is on average during mid- to late October. Clutch size ranges from 3–8 eggs, which are laid asynchronously at an average interval of 2.1 days; the eggs are white and slightly shiny and measure 28 x 23 mm. The mean incubation period is 19.7 days, and ranges from 16–28 days. Only the mother incubates the eggs. The eggs hatch around mid-December; on average 3.6 eggs successfully hatch. There is a bias towards female nestlings, as 41.8% of young are male. For the first six days, only the mother feeds the nestlings. After this time, both parents feed them. The young become independent in February, after which they spend a few more weeks with their parents before departing to become part of a flock of juveniles. Juveniles reach maturity (gain adult plumage) at 16 months of age.