Characteristic features of parrots include a strong, curved bill, an upright stance, strong legs, and clawed zygodactyl feet. Many parrots are vividly coloured, and some are multi-coloured. Most parrots exhibit little or no sexual dimorphism in the visual spectrum. They form the most variably sized bird order in terms of length. The most important components of most parrots' diets are seeds, nuts, fruit, buds, and other plant material. A few species sometimes eat animals and carrion, while the lories and lorikeets are specialised for feeding on floral nectar and soft fruits. Almost all parrots nest in tree hollows (or nest boxes in captivity), and lay white eggs from which hatch altricial (helpless) young.
Parrots, along with ravens, crows, jays, and magpies, are among the most intelligent birds, and the ability of some species to imitate human voices enhances their popularity as pets. Trapping wild parrots for the pet trade, as well as hunting, habitat loss, and competition from invasive species, has diminished wild populations, with parrots being subjected to more exploitation than any other group of birds. Measures taken to conserve the habitats of some high-profile charismatic species have also protected many of the less charismatic species living in the same ecosystems.
Psittaciform diversity in South America and Australasia suggests that the order may have evolved in Gondwana, centred in Australasia.[3] The scarcity of parrots in the fossil record, however, presents difficulties in confirming the hypothesis, and there is currently a higher amount of fossil remains from the northern hemisphere in the early Cenozoic.[4] Molecular studies suggest that parrots evolved approximately 59 million years ago (Mya) (range 66–51 Mya) in Gondwana. The three major clades of Neotropical parrots originated about 50 Mya (range 57–41 Mya).[5]
A single 15 mm (0.6 in) fragment from a large lower bill (UCMP 143274), found in deposits from the Lance Creek Formation in Niobrara County, Wyoming, had been thought to be the oldest parrot fossil and is presumed to have originated from the Late Cretaceous period, which makes it about 70 million years old.[6] However, other studies suggest that this fossil is not from a bird, but from a caenagnathid oviraptorosaur (a non-avian dinosaur with a birdlike beak), as several details of the fossil used to support its identity as a parrot are not actually exclusive to parrots, and it is dissimilar to the earliest-known unequivocal parrot fossils.[7][8]Living species range in size from the buff-faced pygmy parrot, at under 10 g (0.4 oz) in weight and 8 cm (3.1 in) in length,[21]:149 to the hyacinth macaw, at 1 m (3.3 ft) in length,[27] and the kakapo, at 4.0 kg (8.8 lb) in weight.[28] Among the superfamilies, the three extant Strigopoidea species are all large parrots, and the cockatoos tend to be large birds, as well. The Psittacoidea parrots are far more variable, ranging the full spectrum of sizes shown by the family.[28]
The most obvious physical characteristic is the strong, curved, broad bill. The upper mandible is prominent, curves downward, and comes to a point. It is not fused to the skull, which allows it to move independently, and contributes to the tremendous biting pressure the birds are able to exert. A large macaw, for example, has a bite force of 35 kg/cm2 (500 lb/sq in), close to that of a large dog.[29] The lower mandible is shorter, with a sharp, upward-facing cutting edge, which moves against the flat portion of the upper mandible in an anvil-like fashion. Touch receptors occur along the inner edges of the keratinised bill, which are collectively known as the "bill tip organ", allowing for highly dexterous manipulations. Seed-eating parrots have a strong tongue (containing similar touch receptors to those in the bill tip organ), which helps to manipulate seeds or position nuts in the bill so that the mandibles can apply an appropriate cracking force. The head is large, with eyes positioned high and laterally in the skull, so the visual field of parrots is unlike any other birds. Without turning its head, a parrot can see from just below its bill tip, all above its head, and quite far behind its head. Parrots also have quite a wide frontal binocular field for a bird, although this is nowhere near as large as primate binocular visual fields.[30]
Parrots have strong zygodactyl feet with sharp, elongated claws, which are used for climbing and swinging. Most species are capable of using their feet to manipulate food and other objects with a high degree of dexterity, in a similar manner to a human using their hands. A study conducted with Australian parrots has demonstrated that they exhibit "handedness", a distinct preference with regards to the foot used to pick up food, with adult parrots being almost exclusively "left-footed" or "right-footed", and with the prevalence of each preference within the population varying by species.[31]
Cockatoo species have a mobile crest of feathers on the top of their heads, which they can raise for display, and retract.[32] No other parrots can do so, but the Pacific lorikeets in the genera Vini and Phigys can ruffle the feathers of the crown and nape, and the red-fan parrot (or hawk-headed parrot) has a prominent feather neck frill that it can raise and lower at will. The predominant colour of plumage in parrots is green, though most species have some red or another colour in small quantities. Cockatoos, however, are predominately black or white with some red, pink, or yellow.[33] Strong sexual dimorphism in plumage is not typical among parrots, with some notable exceptions, the most striking being the eclectus parrot.[21]:202–207 However it has been shown that some parrot species exhibit sexually dimorphic plumage in the ultraviolet spectrum, normally invisible to humans.[34][35]
Distribution and habitat
Parrots are found on all tropical and subtropical continents and regions including Australia and Oceania, South Asia, Southeast Asia, Central America, South America, and Africa. Some Caribbean and Pacific islands are home to endemic species.[36] By far the greatest number of parrot species come from Australasia and South America.[37] The lories and lorikeets range from Sulawesi and the Philippines in the north to Australia and across the Pacific as far as French Polynesia, with the greatest diversity being found in and around New Guinea.[36] The subfamily Arinae encompasses all the neotropical parrots, including the amazons, macaws, and conures, and ranges from northern Mexico and the Bahamas to Tierra del Fuego in the southern tip of South America.[38] The pygmy parrots, tribe Micropsittini, form a small genus restricted to New Guinea and the Solomon Islands.[39] The superfamily Strigopoidea contains three living species of aberrant parrots from New Zealand.[40] The broad-tailed parrots, subfamily Platycercinae, are restricted to Australia, New Zealand, and the Pacific islands as far eastwards as Fiji.[41] The true parrot superfamily, Psittacoidea, includes a range of species from Australia and New Guinea to South Asia and Africa.[36] The centre of cockatoo biodiversity is Australia and New Guinea, although some species reach the Solomon Islands (and one formerly occurred in New Caledonia),[42] Wallacea and the Philippines.[43]
Several parrots inhabit the cool, temperate regions of South America and New Zealand. Three species—the Thick-billed parrot, the Green parakeet, and the now-extinct Carolina parakeet—have lived as far north as the southern United States. Many parrots have been introduced to areas with temperate climates, and have established stable populations in parts of the United States (including New York City),[44] the United Kingdom,[45] Belgium,[46] Spain[47][48] and Greece.[49] These birds can be quite successful in introduced areas, such as the non-native population of red-crowned amazons in the U.S. which may rival that of their native Mexico.[50] The only parrot to inhabit alpine climates is the Kea, which is endemic to the Southern Alps mountain range on New Zealand's South Island.[51]
Few parrots are wholly sedentary or fully migratory. Most fall somewhere between the two extremes, making poorly understood regional movements, with some adopting an entirely nomadic lifestyle.[52] Only three species are migratory – the orange-bellied, blue-winged and swift parrots.[53]
Behaviour
Numerous challenges are found in studying wild parrots, as they are difficult to catch and once caught, they are difficult to mark. Most wild bird studies rely on banding or wing tagging, but parrots chew off such attachments.[52] Parrots also tend to range widely, and consequently many gaps occur in knowledge of their behaviour. Some parrots have a strong, direct flight. Most species spend much of their time perched or climbing in tree canopies. They often use their bills for climbing by gripping or hooking on branches and other supports. On the ground, parrots often walk with a rolling gait.[30]
Diet
The diet of parrots consists of seeds, fruit, nectar, pollen, buds, and sometimes arthropods and other animal prey. The most important of these for most true parrots and cockatoos are seeds; the large and powerful bill has evolved to open and consume tough seeds. All true parrots, except the Pesquet's parrot, employ the same method to obtain the seed from the husk; the seed is held between the mandibles and the lower mandible crushes the husk, whereupon the seed is rotated in the bill and the remaining husk is removed.[52] They may use their foot sometimes to hold large seeds in place. Parrots are granivores rather than seed dispersers, and in many cases where they are seen consuming fruit, they are only eating the fruit to get at the seed. As seeds often have poisons that protect them, parrots carefully remove seed coats and other chemically defended fruit parts prior to ingestion. Many species in the Americas, Africa, and Papua New Guinea consume clay, which releases minerals and absorbs toxic compounds from the gut.[54]
Geographical range and body size predominantly explains diet composition of Neotropical parrots rather than phylogeny.[55]
Lories, lorikeets, hanging parrots, and swift parrots are primarily nectar and pollen consumers, and have tongues with brush tips to collect it, as well as some specialised gut adaptations. Many other species also consume nectar when it becomes available.[56][57]
Some parrot species prey on animals, especially invertebrate larvae. Golden-winged parakeets prey on water snails,[58] the New Zealand kea can, though uncommonly, hunts adult sheep,[59] and the Antipodes parakeet, another New Zealand parrot, enters the burrows of nesting grey-backed storm petrels and kills the incubating adults.[60] Some cockatoos and the New Zealand kaka excavate branches and wood to feed on grubs; the bulk of the yellow-tailed black cockatoo's diet is made up of insects.[61]
Some extinct parrots had carnivorous diets. Pseudasturids were probably cuckoo- or puffbird-like insectivores, while messelasturids were raptor-like carnivores.[14]
Breeding
With few exceptions, parrots are monogamous breeders who nest in cavities and hold no territories other than their nesting sites.[52][62] The pair bonds of the parrots and cockatoos are strong and a pair remains close during the nonbreeding season, even if they join larger flocks. As with many birds, pair bond formation is preceded by courtship displays; these are relatively simple in the case of cockatoos. In Psittacidae parrots' common breeding displays, usually undertaken by the male, include slow, deliberate steps known as a "parade" or "stately walk" and the "eye-blaze", where the pupil of the eye constricts to reveal the edge of the iris.[52] Allopreening is used by the pair to help maintain the bond. Cooperative breeding, where birds other than the breeding pair help raise the young and is common in some bird families, is extremely rare in parrots, and has only unambiguously been demonstrated in the El Oro parakeet and the golden parakeet (which may also exhibit polygamous, or group breeding, behaviour with multiple females contributing to the clutch).[63]
Only the monk parakeet and five species of lovebirds build nests in trees,[64] and three Australian and New Zealand ground parrots nest on the ground. All other parrots and cockatoos nest in cavities, either tree hollows or cavities dug into cliffs, banks, or the ground. The use of holes in cliffs is more common in the Americas. Many species use termite nests, possibly to reduce the conspicuousness of the nesting site or to create a favourable microclimate.[65] In most cases, both parents participate in the nest excavation. The length of the burrow varies with species, but is usually between 0.5 and 2 m (1.6 and 6.6 ft) in length. The nests of cockatoos are often lined with sticks, wood chips, and other plant material. In the larger species of parrots and cockatoos, the availability of nesting hollows may be limited, leading to intense competition for them both within the species and between species, as well as with other bird families. The intensity of this competition can limit breeding success in some cases.[66][67] Hollows created artificially by arborists have proven successful in boosting breeding rates in these areas.[68] Some species are colonial, with the burrowing parrot nesting in colonies up to 70,000 strong.[69] Coloniality is not as common in parrots as might be expected, possibly because most species adopt old cavities rather than excavate their own.[70]
The eggs of parrots are white. In most species, the female undertakes all the incubation, although incubation is shared in cockatoos, the blue lorikeet, and the vernal hanging parrot. The female remains in the nest for almost all of the incubation period and is fed both by the male and during short breaks. Incubation varies from 17 to 35 days, with larger species having longer incubation periods. The newly born young are altricial, either lacking feathers or with sparse white down. The young spend three weeks to four months in the nest, depending on species, and may receive parental care for several months thereafter.[71]
As typical of K-selected species, the macaws and other larger parrot species have low reproductive rates. They require several years to reach maturity, produce one or very few young per year, and do not necessarily breed every year.[72]:125
Intelligence and learning
Some grey parrots have shown an ability to associate words with their meanings and form simple sentences. Along with crows, ravens, and jays (family Corvidae), parrots are considered the most intelligent of birds. The brain-to-body size ratio of psittacines and corvines is comparable to that of higher primates.[73] Instead of using the cerebral cortex like mammals, birds use the mediorostral HVC for cognition.[74] Not only have parrots demonstrated intelligence through scientific testing of their language-using ability, but also some species of parrots, such as the kea, are also highly skilled at using tools and solving puzzles.[75]
Learning in early life is apparently important to all parrots, and much of that learning is social learning. Social interactions are often practised with siblings, and in several species, crèches are formed with several broods. Foraging behaviour is generally learnt from parents, and can be a very protracted affair. Generalists and specialists generally become independent of their parents much quicker than partly specialised species who may have to learn skills over long periods as various resources become seasonally available. Play forms a large part of learning in parrots; play can be solitary or social. Species may engage in play fights or wild flights to practice predator evasion. An absence of stimuli can delay the development of young birds, as demonstrated by a group of vasa parrots kept in tiny cages with domesticated chickens from the age of 3 months; at 9 months, these birds still behaved in the same way as 3-month-olds, but had adopted some chicken behaviour.[52] In a similar fashion, captive birds in zoo collections or pets can, if deprived of stimuli, develop stereotyped and harmful behaviours like self-plucking. Aviculturists working with parrots have identified the need for environmental enrichment to keep parrots stimulated.[76]
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