Eastern Rosella

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). 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. 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.

The eastern rosella (Platycercus eximius) has become naturalised in New Zealand. 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 Kūiti, 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 Eketāhuna, and west to Ōtaki by 1985. Sightings also have been reported in the areas like New Plymouth, Taupō, Gisborne, Tiritea, Banks Peninsula, Nelson area, and Stewart Island. 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.

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

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 Manawatū, 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.

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

Being an arboreal bird, the eastern rosella mostly feed on grass seeds, buds, flowers, nectars, fruits, as well as insects and their larvae. 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. 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. 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. This appears to be a trade off between meeting their nutritional needs through the plants while encountering those harmful compounds.

In Australia, eastern rosella usually breeds from August to January–February. 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. 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. The fledging period usually begins in early December and ends in early February.

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. Less frequent of nests visits are often relates to higher predation rate, thus contributing to higher nest failures and lower breeding success. The rate of nest attendance is also influenced by the diet of the young. 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. 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. Availability of nesting boxes could help this species to compete with the introduced common myna.

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. 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. 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. 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. 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. 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. Additionally, having a few unutilized nests around decreases the chance of the predator locating the right nest. However, poor alternative nesting sites of eastern rosella like burrows, gate posts and tree stumps which are usually located in lower areas, do expose themselves to flooding. It has been found that dominant female eastern rosellas would destroy the subordinate females' eggs to avoid them from having a successful breeding.

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. However, their activities are limited and influenced by the surroundings of the nests. 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. 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.

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. 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.