Eastern rosella

Eastern rosella
P. e. diemenensis (male)
P. e. diemenensis (female)
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Psittaciformes
Family:	Psittaculidae
Genus:	Platycercus
Species:	P. eximius
Binomial name
Platycercus eximius (Shaw, 1792)

The eastern rosella (Platycercus eximius) is a parrot native and endemic to south-eastern Australia. It was first introduced to New Zealand in cages, which then both intentionally released and accidentally escaped into the wild^[2] and has been found establishing mainly in the North Island^[3] (notably in the northern half of the island, Taranaki, Waikato and in the Hutt Valley) and in the hills around Dunedin in the South Island^[4][5] since the early 20th century.^[6]

P.eximius (Eastern Rosella) is located under the genus Platycercus and subgenus Violania along with other three species members: P.venustus (Northern Rosella), P.adscitus (Pale-headed Rosella) and P.icterotis (Western Rosella).^[7] An early analysis of rosella phylogeny stated that the taxa of eastern rosella and pale-headed rosella are most closely related to each other compared to the other two rosella species.^[7][8] Then, the hybrids of the two taxa have been recorded in northeastern New South Wales and southeastern Queensland, as both species have been recorded habituating in the same ecological area ranges, differ from the other two species^[8] However, a mitochondrial study published in 2017 found that the eastern rosella was the earlier offshoot of the lineage that split into the pale-headed and northern rosellas and those non-sister taxa were hence able to hybridize.^[7]

The three subspecies of eastern rosella are:

• P. e. eximius, which is mainly found in Victoria and southern New South Wales, Australia. The black feathers on the back have green margins, and its rump is pale green.
• P. e. elecica, which is found in northeast New South Wales and southeast Queensland. For males, the black feathers on the back have golden-yellow margins, but greenish yellow in the female. For both sexes the rump is bluish-green. This subspecies is also called the golden-mantled rosella, often abbreviated to GMR.
• P. e. diemenensis, mostly found in eastern Tasmania. White cheek patches are larger and the red on the head is darker.^[9]

The length of eastern rosella is 30 cm (12 in). Its cheeks are white, and it has a red colored head. The beak is white, and the irises are brown. Its upper breast is red, and its lower breast is yellow and fades to pale green over the abdomen. The black feathers on the back and shoulders have yellowish and greenish margins which gives the scalloped look that differs between the sexes and subspecies. Moreover, the wings and lateral tail feathers are bluish while the tail is dark green. Meanwhile, their legs are grey. For the females, it is the same with males which is duller in coloration and has an underwing stripe, but is not present in the adult male. The colour of their young is duller than the females and has an underwing stripe.^[9]

The eastern rosella (Platycercus eximius) has become naturalised in New Zealand.^[3] Its first introduction occurred around 1910, when a small shipment of eastern rosellas, as well as a few crimson rosellas (P. elegans), was prohibited entry into New Zealand by the Customs Department. The shipment was released off Otago Heads by the ship returning to Sydney.^[10] There were approximately 12 birds escaped in Dunedin when their cages were damaged in a gale.^[11]

By the 1970s, the population of eastern rosella had become well-established throughout Auckland, Northland, and the far north, extending into western Waikato as far south as Kawhia and Te Kuiti, and east to the Coromandel Peninsula. The species also seen in the Wellington-Hutt Valley Region, and also started colonizing the foothills of the Tararua Range, extending east to Eketahuna, and west to Ōtaki by 1985.^[12] Sightings also have been reported in the areas like New Plymouth, Taupo, Gisborne, Tiritea, Banks Peninsula, Nelson area, and Stewart Island.^[13] In Otago which located in the South Island, the eastern rosella population has remained relatively small, in contrast to North Island populations, which have widely distributed and currently covering most of the Island. On top of that, it has been reported that the meta-population of eastern rosella in New Zealand arose from three main sites of establishment: Dunedin, Auckland, and Wellington.^[2]

Eastern rosellas was well-distributed in Dunedin by the 1930s, and between 1940s and 1950s, they have been sighted to spread across Otago. However, from 1950 to 1970s, the sightings of eastern rosella in Otago decreased, as the population was reported to be in decline^[2][11] The decrease of the population number attributed to the poisoning of rabbits with strychnine and grain, and also due to manmade traps for aviaries.^[11] Nevertheless, since 1980s, there has been an increase in the sightings of the species, which reflects a recovery of eastern rosella population in Dunedin.^[2]

In 1960s, eastern rosellas mainly spread across the mid until the upper of Northland areas. Then, by 1970s this species have been reported to spread around Waikato, followed by Coromandel, the Bay of Plenty and Taranaki. Plus, during 1975-76 the records of eastern rosella in the areas of mid-Coromandel and Waiheke Island suggest that they are most likely spread to the Coromandel Peninsula from Waikato. Plus, during the early colonisation in Taranaki, this species was more commonly seen in Waikato compared to Manawatu, which suggests that the eastern rosella population in Taranaki expanded southward from Auckland, with recent observations that shows a continuous presence in the western North Island.^[2]

The increase in the population of eastern rosella in Wellington led to further spread into northern Wellington, Manawatu and Waitapa, which was reflected by their establishment and common sightings. However, in Mana Islands and Kapiti, there were no species of eastern rosella that has been sighted.^[2] 12/2024: There is a good wild population around the Waikanae area, breeding sites especially near the beach in bush areas.

Generally, eastern rosella appears to live in lower strata instead of higher areas.^[14] In New Zealand, they occupy along the edges or remnant patches in open woodland and forest areas, surrounding the shelter belts, gumlands, and also in orchards. Plus, eastern rosella also frequently observed in cultivated exotic crops and town areas.^[15] They also prefer inhabiting well-maintained lawns such as at the gardens and golf courses.^[14] In Wellington, they are regularly spotted in open areas in the cities as well as agricultural lands, which are same favourable areas reported in both New Zealand and Australia.^[15][2]

Being an arboreal bird, the eastern rosella mostly feed on grass seeds, buds, flowers, nectars, fruits, as well as insects and their larvae.^[2] Their diet composed wide range of food, and it was outlined that eastern rosella feeds on 50 different plant species as well as 15 species of animals, including a wide range of on-ground food items.^[16] As eastern Rosellas forage across variety of food types, they are capable of having numerous of foraging positions or more likely to be an ambidextrous.^[17] Across these varied diets, it includes both native and non-native plant species in New Zealand such as eucalypts (Eucalyptus spp.), ngaio (Myoporum laetum), willow (Salix spp.), poplar (Populus spp.), and karaka (Corynocarpus laevigatus). Nevertheless, foraging on these food resources expose eastern rosella to harmful compounds such as toxins, which are being produced in the plants as their defence mechanisms.^[2][18] Despite having the ability to avoid food which contains high level of toxins, there is still a measurable concentration of toxins in the diet of Eastern Rosella.^[19] This appears to be a trade off between meeting their nutritional needs through the plants while encountering those harmful compounds.^[18] Eastern rosella consumption of non-food substance like charcoal, or a type of geophagy, often relates to immobilising the toxic compounds such as phenol, while enabling the process the absorption and digestion of protein at the same time.^[20][21]

In Australia, eastern rosella usually breeds from August to January–February.^[22] As eastern rosella is known as a cavity nester, they often build their nests mainly in the hollows of tree trunks, limbs, fallen logs or tree stumps, gateposts, and nest boxes. Occasionally, they also nest in other locations like wall cavities in buildings as well as rabbit burrows. Female eastern rosella will lay 5 to 6 eggs on average, at intervals of 1 to 3 days.^[10] The eggs are usually laid in mid-November and mid-December and soon after they are laid, they will be incubated for about 18 to 22 days, until they reach the fledging period, which happens about 30 to 33 days.^[10][23] The fledging period usually begins in early December and ends in early February.^[23] Usually, female eastern rosellas are said to lay two broods, with up to twelve offspring in every season.^[24]

In urban areas, eastern rosella were reported to face higher disturbances from other cavity-nesting birds, that leads them to infrequently visit to their nests, for instance, in the form of nest boxes.^[25] Less frequent of nests visits are often relates to higher predation rate, thus contributing to higher nest failures and lower breeding success.^[26][27] The rate of nest attendance is also influenced by the diet of the young.^[28] Other than predation rates, lower nest visitations could be explained by the ability of eastern rosella to feed on many food items during each visit, before returning to their young and transferring the partially ingested food.^[29]

Nevertheless, the presence of additional nesting sites could support the spread of the eastern rosella population and their establishment in urban areas. When provided with additional artificial nesting boxes over multiple period of breeding seasons, eastern rosellas were observed to occupy more of these particular nesting sites. As a result, this could be a way to improve the breeding success of eastern rosella and protect this endangered parrot species in Australia.^[30]

The characteristic of eastern rosella as a cavity nester contributes to its successful breeding, as they will minimize the amount of energy they spend while building their nest and thermoregulation activity. Cavity-nesting tends to result in a bigger clutch size and less predator threats.^[31] Nevertheless, being an introduced species in New Zealand, the establishment of eastern rosella as a cavity nester affects the native cavity-nesting species as the distribution of these types of species depends on the availability of nest sites.^[32] Presently, eastern rosella and other widely distributed cavity-nesting species in New Zealand such as common myna (Acridotheres tristis) appear to be a threat to native ones, due to expansion and geographical distribution.^[33] In Northland of New Zealand, eastern rosella was outlined as the most distributed parrot, which results in a great competition in nest cavities and food resources with kākāriki species. Moreover, from the 1950s to 1960s, the reduction in the number of yellow-crowned parakeet (Cyanoramphus aurlceps) that habituated in some forests in the Northlands was said to be the result of the arrival of eastern rosella in that particular area which outcompete the nesting sites and food resources.^[34]

When choosing a suitable location to breed, the presence of water sources close to the nesting site is one of the preferences for eastern rosella. Being near the water sources is advantageous for them not only to ease them to get access to water, but also to minimize their energy expenditure and time spent searching for it.^[35] In addition, the eastern rosella prefers nesting in areas with presence of other accessible nests, as this increases the probability of finding the right breeding site.^[35] The availability of several nests in the same area serves as alternatives, making it easier for them to rebuild a new nest if the old one is damaged or taken over.^[36] Additionally, having a few unutilized nests around decreases the chance of the predator locating the right nest.^[37] However, poor alternative nesting sites of eastern rosella like burrows, gate posts and tree stumps^[15] which are usually located in lower areas, do expose themselves to flooding.^[32] This affects the growth of their chicks and sometimes could lead to death.^[15]

However, when the nests are too close in proximity from one breeding pair to another, there is a high chance that it leads to agonistic interactions and fights. Hence, rosellas will defend zone around their nests, for example including nearby trees to make sure that no other pairs settled within the particular area.^[38] It has been found that dominant female eastern rosellas would destroy the subordinate females' eggs to avoid them from having a successful breeding.^[39]

The nestling period of eastern rosella chicks is quite short, which followed by fledging period after 28 to 30 days, and become fully independent between 45 and 60 days post-hatching.^[40] Approaching the last quarter of nestling period, approximately 20 days after hatching, the chicks are able to stand and exhibit well-coordinated perching. By the end of the nestling period, they can walk properly on even surfaces and perform other activities such as climbing, grooming, and flapping their wings.^[41] However, their activities are limited and influenced by the surroundings of the nests.^[42]

At the beginning of the fledging period, around 29 to 35 days post-hatching, the locomotion of young eastern rosellas develops rapidly. This portrays in the well-performed climbing activity and their ability in turning around from an elevated spot. They also began to practice flying. The development of these activities also have observed for other chicks with different bird species.^[41][43] After improving locomotion, the chicks then further improved to be able to preen their feathers properly, and eventually manage to handle items using their both upper and lower mandibles.^[41]

From day 36 onwards, the birds were considered to be independent, and continue to improve their motor skills related to feeding behaviour, for example in handling items with their beaks and feet. They also manage to perform other activities related to body maintenance, excluding bathing.^[41] In terms of activity related to feeding behaviour, it is necessary for the chicks to do it perfectly, not only for practice, but also would help them under stress conditions, such as when identifying edible items.^[41][44]

Eastern rosella often rest during the day, and scattering among the trees. They often fly in groups of 10 to 20 birds, among the trees up to three acres. In the afternoon, eastern rosellas will usually transition from resting period to maintenance period, performing activities such as preening and urinating. Then, they often fly to feeding sites to forage in a pair, resulting to noticeable wider spacing among small groups within the larger flock. During feeding, aggression could be seen among eastern rosella as they compete for food. There are also alarms ranging from mild level, where they simply keep only their heads up without moving their bodies, to the high level or increase in alarm which usually results in a fight.^[40]

In the evening, eastern rosella would fly to their roosting areas, with the presence of leading alarm. The feeding flocks of eastern rosella then resulting in a bigger number. At night, they then shift from feeding mode to mainly maintenance mode. Plus, calling activity peaks during the night, before they settle down with resting mode. Throughout the night, eastern rosellas exhibit least activity until the morning arrives. As soon as the sun comes out, they fly in small groups and spread among the trees to forage.^[40]

• 
  The eastern rosella may be easily recognised by its distinctive back plumage.
• 
  Juvenile of eastern rosella
• 
  Egg of eastern rosella - MHNT
• 
  Chicks of eastern rosella

• Simpson, K.; Day, N. (2004). Field Guide to the Birds of Australia (7th ed.). Viking. ISBN 0-670-04180-7.

Wikimedia Commons has media related to Platycercus eximius.

Wikispecies has information related to Platycercus eximius.

• "Platycercus (Violania) eximius (Shaw, 1792) Eastern Rosella". Atlas of Living Australia.
• Original description and illustration in Shaw and Nodder's Naturalist's Miscellany.