Kiwi Bird

Kiwi is any of five species of kiwi flightless birds that belong to the genus Apteryx are found in New Zealand. This term is the Maori word referring to the male's shrill call. Kiwis are grayish-brown birds, and they are the size of a chicken and are related to the extinct moas. Kiwis are most unusual in several respects: vestigial wings are hidden within the plumage; nostrils are at the tip (rather than the base) of the long and flexible bill; the feathers that have no aftershafts are hair-like and soft; the legs are muscular and stout, and each of the four toes contains a large claw.

Kiwi Bird Description

Their adaptation to terrestrial life is more extensive: they lack the keel on the sternum that connects the anchor wing muscles, as do all other ratites (emu, ostrich, cassowary, and rhea). The vestigial wings are so little that they are hidden behind the bristly, two-branched feathers that resemble hair. While many adult birds have bones with hollow insides to minimize weight and make flight practicable, Kiwi holds marrow, like mammals and the young of the other birds.

With no constraints on weight because of flight requirements, brown kiwi females carry and lay the single egg that can weigh 450 g (16 oz) on the highest case. Like most of the other ratites, they have no uropygial gland (or the preen gland). Their bill is pliable, long, sensitive to touch, and their eyes have a reduced pecten. Their feathers lack aftershafts and barbules, and they have large vibrissae up to the gape. They hold 13 flight feathers, small pygostyle with no tail. Their caecum is long and narrow, and their gizzard is weak.

The below representation (Clockwise from left - brown kiwi (Apteryx australis), a little spotted kiwi (Apteryx owenii), and the great spotted Kiwi (Apteryx haastii) at Auckland War Memorial Museum).

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In all avian species, the Kiwi's eye is the smallest in terms of body mass, resulting in the narrowest visual field. The eye has small specializations for a nocturnal lifestyle, but Kiwi relies more heavily on their other senses (auditory, olfactory, and somatosensory system). The Kiwi's vision is so poor that blind animals have been found in the wild, demonstrating how little they rely on sight for life and foraging.

One-third of an A. rowi population in New Zealand with minimal environmental stress experienced ocular lesions in one or both eyes, according to one experiment. The same experiment looked at three individual specimens that were completely blind and discovered that, except for ocular abnormalities, they were in fair physical condition. Despite their enormous size, the Kiwi's closest ancestors, the extinct elephant birds, shared this feature, according to a 2018 study.

Unlike virtually every other palaeognath that is generally small-brained by the bird standards, Kiwi contains proportionally large encephalization quotients. Hemisphere proportions are very similar to those of songbirds and parrots, though there is no piece of evidence of similarly complex behaviour.

Etymology

The Māori language term kiwi is generally accepted to be "of imitative origin" from the call. However, a few linguists derive the term from Proto-Nuclear Polynesian *kiwi that refers to Numenius tahitiensis, the bristle-thighed curlew, which is a migratory bird that winters in the tropical Pacific islands region. With its brown body and long decurved bill, the curlew resembles the Kiwi. So whenever the first Polynesian settlers arrived, they could have applied the word Kiwi to the new-found bird. The genus name Apteryx has derived from an Ancient Greek "without wing": a-, "not" or "without"; pterux, "wing."

This name is normally not capitalised, and the plural is either the anglicised "kiwis" or "kiwi" without a "s" in Mori.

Taxonomy and Systematics

Although it was long presumed that Kiwi was closely related to some other New Zealand ratites, the moa, some recent DNA studies have identified its closest relative since the extinct elephant bird of Madagascar, and among the extant ratites, the Kiwi is very closely related to the cassowaries and emu than to the moa.

Research, which is published in 2013 on an extinct genus, Proapteryx, which is known from the Miocene deposits of the Saint Bathans Fauna, had found that it was smaller and probably capable of flight by supporting the hypothesis, which the Kiwi's ancestor reached New Zealand independently from that of moas that were already flightless and large by the time kiwi appeared.

Species

There are five known species of Kiwi and a number of subspecies as well. They are given below.

Haastii

This is the largest species that stands up to 45 cm (18 in) high and weighs up to 3.3 kg (7.3 lb) (males about 2.4 kg (5.3 lb)). It holds grey-brown plumage with lighter bands. The female lays only one egg that both parents then incubate. Their population is estimated to be around 20,000, distributed through the more mountainous parts of the northern West Coast, northwest Nelson, and the Southern Alps.

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Owenii

The small little spotted Kiwi, which is unable to withstand predation by the introduced pigs, cats, and stoats that have led to its extinction on the mainland. Up to 1350 remain completely on Kapiti Island. Also, it has been introduced to the other predator-free islands and appears to be becoming established with up to 50 'Little Spots' on every island.

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Australis

The southern brown Kiwi is a relative kiwi's common species. Approximately it is the size of the great spotted Kiwi and also the same in appearance as the brown Kiwi, but its plumage will be lighter in colour.

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Rowi

In 1994, the Okarito kiwi, which was first identified as a new species, is slightly smaller, with a greyish tinge to the plumage and, at times, white facial feathers (white kiwi bird). Females lay as many as three eggs in the season, each one in a different nest. Both male and female incubate.

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Mantelli

The North Island brown kiwi, Apteryx or Apteryx Mantelli australis before 2000 (and still in a few sources), is widespread in the northern two-thirds of the North Island and, with up to 35,000 remainings, is given as the most common Kiwi. Females stand up to 40 cm (16 inches) high, and the males weigh about 2.2 kg (4.9 lb) and females about 2.8 kg (6.2 lb).

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Behaviour and Ecology

In the 13th century or earlier, before the arrival of humans, the only endemic mammals of New Zealand were three species of bat, and the ecological niches in the other parts of the world were filled by creatures as diverse as wolves, horses, and mice were taken up by the birds (and, to a lesser extent, insects, reptiles, and gastropods).

Kiwi's mostly nocturnal habits can be a result of habitat intrusion by predators, including humans. In New Zealand, areas where introduced predators have been removed, such as sanctuaries, Kiwi are often seen in the times of daylight. They usually prefer subtropical and beech forests and temperate podocarp, but they are being forced to adapt to multiple habitats, such as tussock grassland, sub-alpine scrub, and the mountains. Kiwi contains a highly developed sense of smell, which is unusual in a bird, and they are the only birds with nostrils at the end of their long beaks.

Kiwi eats seeds, small invertebrates, grubs, and several varieties of worms. Also, they can eat fruit, eels, small crayfish, and amphibians. Due to this reason, their nostrils are located at the end of their long beaks; Kiwi may locate worms and insects underground with the help of their keen sense of smell, without actually feeling or seeing them.

This sense of smell is because of a highly developed olfactory chamber and the surrounding regions. It is also a common belief that Kiwi relies solely on their sense of smell to catch prey, but this has not been observed scientifically. Various lab experiments have suggested that A. australis may rely on olfaction alone, but it is not consistent under natural conditions. Instead, the Kiwi can rely on auditory and/or vibrotactile cues.

The below figure is the 1860s drawing of Apteryx, which illustrates its distinctive features, including short legs, long beaks, and claws, and dark hair-like feathers.

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Once bonded, a female and male Kiwi tend to live their entire lives as a monogamous couple. In the mating season, from June to March, the pair call to each other at night and meet in the nesting burrow every three days. These relationships can last for around 20 years. They are unusual among the other birds in that, along with a few raptors, they contain a functioning pair of ovaries. (In platypuses and in most birds, the right ovary never matures, so that only the left is given as functional). Kiwi eggs may weigh up to one-quarter compared to the weight of the female.

Usually, just one egg is laid per one season. Kiwi lays one of the largest eggs in proportion to the size of any bird across the world, so even though the Kiwi is up to the size of a domestic chicken, it can be able to lay eggs, which are about six times the size of chicken's egg. These eggs are smooth in texture, and they are greenish-white (white kiwi bird) or ivory. The male usually incubates the egg, except for the great spotted Kiwi, A. haastii, where both parents are involved.

The incubation period is given as 63–92 days. Producing the huge egg places significant physiological stress on the female; it takes thirty days to grow the fully developed egg, the female should eat three times her normal food amount. Either two to three days prior to the egg being laid, there is little space left inside the female for its stomach, and it is forced to fast.

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