The western rosella is
endemic to the southwest of Australia, isolated from sister species of the north and east of the country. Moderately common, it is usually sedentary, frequenting forest and many other types of wooded country or
kwongan. It also occurs in farmland or at other feeding opportunities, and is most often observed at sites cleared of vegetation. The captive occurrence in Australia and several other continents began before 1830 in England. '', first depiction of the species by Edward Lear, November to December 1830, entitled "Platycercus Stanleyii / Stanley Parrakeet", named for the patron Lord Stanley The two subspecies are geographically adjacent—
P. icterotis xanthogenys at the
wheatbelt region, inland to the north and east of the range and
P. icterotis icterotis occurring at coastal areas in the south and west. The inland boundary of the species' range extends from the area between the lower part of the
Swan River and the
Arrowsmith River at the western coast. From there it passes to the east and south before
Southern Cross, the Fraser Range,
Esperance,
Stirling Ranges and
Kojonup. The line of demarcation between the inland and coastal subspecies begins east of King George Sound and lies to the northwest via
Mount Barker and the Kojonup region toward the
Bannister River. The species is less common on the
Swan Coastal Plain than in southern areas of the wheatbelt, where it is more frequently observed around
Narrogin and
Katanning at remnant wandoo woodland, They occur throughout the conservation area at
Dryandra Woodland. Authors came to express doubts on the status of the subspecies, and compiled observations show no geographical separation. The historical records of the species indicate it relatively uncommon, although it has been noted more often in southern regions. The northernmost extent of the distribution range is near
Moora, with records extending toward the east around
Norseman. The population of the species has declined significantly since colonisation, especially the inland
P. icterotis xenogenys after the 1970s. It became locally extinct in
shires where it had previously been recorded, these include:
Coorow,
Dandaragan, Moora,
Dalwallinu,
Merredin,
Quairading,
Serpentine-Jarrahdale and the
Shire of Murray. Population declines have also been recorded in the shires of
Swan,
Kalamunda,
Northam, York,
Armadale-Kelmscott,
Capel and
Dumbleyung. This disappearance at northern and eastern parts of the Wheatbelt is the result of habitat removal, and no shires show an increase in records. The adaptation to introduced agricultural crops has been comparatively limited when contrasted with the range of seeds harvested by ringnecks
Barnardius zonarius and others species. This is likely to have restricted their success in migration to or re-population of greatly altered landscapes. The suggested movement after breeding toward the coast during the austral summer, from areas in the north of the range, lacked evidence of large-scale seasonal movement in occurrence data, The distribution of
P. icterotis icterotis is restricted to humid and subhumid regions, an area south of
Dandaragan and lower reaches of the
Moore River, and to the west of:
Wannamal,
Muchea,
Mundaring,
Jarrahdale,
Marrinup,
Collie,
Boyup Brook,
Hay River (upper), and from the ranges of
Porongurups and Green Range. Records for
P. icterotis xanthogenys are from the southern interior of Western Australia, semiarid climatic zones, that formerly included
Wongan Hills and occurrences at:
Kununoppin,
Moorine Rock,
Parker Range,
Yardina Rock and
Ten Mile Rocks. The range extends to the west at:
Toodyay,
Dale River,
Mt Saddleback and
Kojonup and north of the Stirling Range,
Fitzgerald River (lower),
Ravensthorpe,
Frank Hann National Park and
Red Lake. The occurrence farther north is termed casual, the locations are:
Mt Jackson,
Karalee and
Gnarlbine Rock. A significant change in abundance was noted at
Grass Patch, where it was common in the mid-20th century and reappeared after a fifteen-year absence in later decades. The erroneous locations reported by Mathews, Point Cloates and
Shark Bay, were later admitted to have been incorrect by the author; he also identifies the obvious error in Gould's protologue (1837) in extending the range from
King George Sound to "… New South Wales. etc.". The species was later reported by Gould (1848) as only known at the
Swan River Colony, a location where it is now uncommon. They favour woodland habitat with sheoak (
Allocasuarina), wurak (
Eucalyptus salmonophloia) and wandoo (
Eucalyptus wandoo,
et al), but have sometimes flourished at areas cleared for introduced grain crops in the region's Wheatbelt. They also appear at other cleared areas adjoining bushland, such as roadsides, golf courses and reserves, to harvest grasses or weeds. The subspecies occur in differing types of vegetation, living in
communities associated with their woody upper-storey plants. The coastal subspecies
P. icterotis icterotis is seen amongst the eucalypts and paperbarks of the high rainfall area from
Jurien to
Green Range, east of
Manypeaks, namely marri (
Corymbia calophylla), karri (
Eucalyptus diversicolor), moitch (
E. rudis) and the paperbark (
Melaleuca). They are known to feed on the fruit of
Bossiaea linophylla and
Leucopogon obovatus, the flowers of marris and fleshy part of the seed of
Macrozamia riedlei. The subspecies feeds both on the ground and in trees. The wooded scrub of the lower rainfall inland region inhabited by
P. icterotis xanthogenys is generalised as eucalypt and sheoak, the trees moitch, wandoo (
Eucalyptus wandoo), wurak and in tall
mallee country or the habitat at the rock, or sighing, sheoak (
Allocasuarina huegeliana). This subspecies feeds at seeding wandoo,
Acacia huegeliana,
Glischrocaryon flavescens and
Olearia revoluta and flowering
Eucalyptus eremophila and
Melaleuca acuminata. == Behaviour ==