[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.
[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.
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.
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.
[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.
[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.
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.
[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.
[29] Nevertheless, the presence of additional nesting sites could support the spread of the eastern rosella population and their establishment in urban areas.
[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.
[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.
[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.
[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] 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.
[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.
Then, they often fly to feeding sites to forage in a pair, resulting to noticeable wider spacing among small groups within the larger flock.