Kākāpō
The kākāpō, sometimes known as the owl-parrot, is a species of large, nocturnal, ground-dwelling parrot of the superfamily Strigopoidea. It is endemic to New Zealand.
Kākāpō can be up to long. They have a combination of unique traits among parrots: finely blotched yellow–green plumage, a distinct facial disc, owl-style forward-facing eyes with surrounding discs of specially textured feathers, a large grey beak, short legs, large blue feet, relatively short wings and a short tail. It is the world's only flightless parrot, the world's heaviest parrot, and also is nocturnal, herbivorous, visibly sexually dimorphic in body size, has a low basal metabolic rate, and does not have male parental care. It is the only parrot to have a polygynous lek breeding system. It is also possibly one of the world's longest-living birds, with a reported lifespan of up to 100 years. Adult males weigh around ; the equivalent figure for females is.
The anatomy of the kākāpō typifies the tendency of bird evolution on oceanic islands. With few predators and abundant food, kākāpō exhibit island syndrome development, having a generally robust torso physique at the expense of flight abilities, resulting in reduced shoulder and wing muscles, along with a diminished keel on the sternum. Like many other New Zealand bird species, the kākāpō was historically important to Māori, the indigenous people of New Zealand. It appears in Māori mythology. Heavily hunted in the past, it was used by the Māori both for its meat and for its feathers.
The kākāpō is critically endangered; the total known population of living individuals is Known individuals are named, tagged and confined to four small New Zealand islands, all of which are clear of predators; however, in 2023, a reintroduction to mainland New Zealand was accomplished. Introduced mammalian predators, such as cats, rats, ferrets, and stoats almost wiped out the kākāpō. All conservation efforts were unsuccessful until the Kākāpō Recovery Programme began in 1995.
Taxonomy
The kākāpō was formally described and illustrated in 1845 by the English ornithologist George Robert Gray. He created a new genus and coined the binomial name Strigops habroptilus. Gray was uncertain about the origin of his specimen and wrote, "This remarkable bird is found in one of the islands of the South Pacific Ocean." The type location has been designated as Dusky Sound on the southwest corner of New Zealand's South Island. The generic name Strigops is derived from the Ancient Greek, genitive , and , while its specific epithet habroptilus comes from , and .In 1955 the International Commission on Zoological Nomenclature ruled that the genus name Strigops was feminine. Based on this ruling many ornithologists used the form Strigops habroptila but in 2023 James L. Savage and Andrew Digby argued that under the current ICZN rules the specific epithet should be habroptilus. This view was accepted by ornithologists and in 2024 the International Ornithological Congress Checklist and the eBird/Clements Checklist changed the spelling of the binomial name back to Strigops habroptilus. The species is monotypic, as no subspecies are recognised.
The name kākāpō is Māori, from kākā + pō ; the name is both singular and plural. "Kākāpō" is increasingly written in New Zealand English with the macrons that indicate long vowels. The correct pronunciation in Māori is ; other colloquial pronunciations exist, however. These include the British English , as defined in the Chambers Dictionary in 2003.
The kākāpō is placed in the family Strigopidae together with the two species in the genus Nestor, the kea and the kākā. The birds are endemic to New Zealand. Molecular phylogenetic studies have shown that the family Strigopidae is basal to the other three parrot families in the order Psittaciformes and diverged from them 33–44 million years ago. The common ancestor of the kākāpō and the two Nestor species diverged 27–40 million years ago.
Earlier ornithologists felt that the kākāpō might be related to the ground parrots and night parrot of Australia due to their similar colouration, but this is contradicted by molecular studies; rather, the cryptic colour seems to be adaptation to terrestrial habits that evolved twice convergently.
Description
The kākāpō is a large, rotund parrot. Adults can measure from in length with a wingspan of. Males are significantly heavier than females with an average weight of compared with just for females. Kākāpō are the heaviest living species of parrot and on average weigh about more than the largest flying parrot, the hyacinth macaw.The kākāpō cannot fly, having relatively short wings for its size and lacking the keel on the sternum, where the flight muscles of other birds attach. It uses its wings for balance and to break its fall when leaping from trees. Lighter females are able to perform short glides across gaps in the canopy. Unlike many other land birds, the kākāpō can accumulate large amounts of body fat.
The upper parts of the kākāpō have yellowish moss-green feathers barred or mottled with black or dark brownish grey, blending well with native vegetation. Individuals may have strongly varying degrees of mottling and colour tone and intensity – museum specimens show that some birds had completely yellow colouring. The breast and flank are yellowish-green streaked with yellow. The belly, undertail, neck, and face are predominantly yellowish streaked with pale green and weakly mottled with brownish-grey. Because the feathers do not need the strength and stiffness required for flight, they are exceptionally soft, giving rise to the specific epithet habroptila. The kākāpō has a conspicuous facial disc of fine feathers resembling the face of an owl; thus, early European settlers called it the "owl parrot". The beak is surrounded by delicate feathers which resemble vibrissae or "whiskers"; it is possible kākāpō use these to sense the ground as they walk with its head lowered, but there is no evidence for this. The mandible is variable in colour, mostly ivory, with the upper part often bluish-grey. The eyes are dark brown. Kākāpō feet are large, scaly, and, as in all parrots, zygodactyl. The pronounced claws are particularly useful for climbing. The ends of the tail feathers often become worn from being continually dragged on the ground.
Females are easily distinguished from males as they have a narrower and less domed head, narrower and proportionally longer beak, smaller cere and nostrils, more slender and pinkish grey legs and feet, and proportionally longer tail. While their plumage colour is not very different from that of the male, the toning is more subtle, with less yellow and mottling. Nesting females also have a brood patch of bare skin on the belly.
The kākāpō's altricial young are first covered with greyish white down, through which their pink skin can be easily seen. They become fully feathered at approximately 70 days old. Juvenile individuals tend to have duller green colouration, more uniform black barring, and less yellow present in their feathers. They are additionally distinguishable because of their shorter tails, wings, and beaks. At this stage, they have a ring of short feathers surrounding their irises that resembles eyelashes.
Like many other parrots, kākāpō have a variety of calls. As well as the booms and chings of their mating calls, they will often loudly skraark.
The kākāpō has a well-developed sense of smell, which complements its nocturnal lifestyle. It can distinguish between odours while foraging, a behaviour reported in only one other parrot species. The kākāpō has a large olfactory bulb ratio indicating that it does, indeed, have a more developed sense of smell than other parrots. One of the most striking characteristics of the kākāpō is its distinct musty-sweet odour. The smell often alerts predators to the presence of kākāpō.
As a nocturnal species, the kākāpō has adapted its senses to living in darkness. Its optic tectum, nucleus rotundus, and entopallium are smaller in relation to its overall brain size than those of diurnal parrots. Its retina shares some qualities with that of other nocturnal birds but also has some qualities typical of diurnal birds, lending to best function around twilight. These modifications allow the kākāpō to have enhanced light sensitivity but with poor visual acuity.
Internal anatomy
The skeleton of the kākāpō differs from other parrots in several features associated with flightlessness. Firstly, it has the smallest relative wing size of any parrot. Its wing feathers are shorter, more rounded, less asymmetrical, and have fewer distal barbules to lock the feathers together. The sternum is small and has a low, vestigial keel and a shortened spina externa. As in other flightless birds and some flighted parrots, the furcula is not fused but consists of a pair of clavicles lying in contact with each coracoid. As in other flightless birds, the angle between the coracoid and sternum is enlarged. The kākāpō has a larger pelvis than other parrots. The proximal bones of the leg and wing are disproportionately long and the distal elements are disproportionately short.The pectoral musculature of the kākāpō is also modified by flightlessness. The pectoralis and supracoracoideus muscles are greatly reduced. The propatagialis tendo longus has no distinct muscle belly. The sternocoracoideus is tendinous. There is an extensive cucularis capitis clavicularis muscle that is associated with the large crop.
Genetics
Because kākāpō passed through a genetic bottleneck, in which their world population was reduced to 49 birds, they are extremely inbred and have low genetic diversity. This manifests in lower disease resistance and infertility problems: 61% of kākāpō eggs fail to hatch. Beginning in 2015, the Kākāpō 125+ project has sequenced the genome of all living kākāpō, as well as some museum specimens. The project is a collaboration led by Genomics Aotearoa and a collaboration with a team of international collaborators.A DNA sequence analysis was performed on 35 kākāpō genomes of the surviving descendants of an isolated island population, and on 14 genomes, mainly from museum specimens, of the now extinct mainland population. An analysis of the long-term genetic impact of small population size indicated that the small island kākāpō population had a reduced number of harmful mutations compared to the number in mainland individuals. It was hypothesized that the reduced mutational load of the island population was due to a combination of genetic drift and the purging of deleterious mutations through increased inbreeding and purifying selection that occurred since the isolation of this population from the mainland about 10,000 years ago. Purging of deleterious mutations occurs when there is selection against recessive or partially recessive detrimental alleles as they are expressed in the homozygous state.