The kagu or cagou (Rhynochetos jubatus) is a crested, long-legged, and bluish-grey bird endemic to the dense mountain forests of New Caledonia. It is the only surviving member of the genus Rhynochetos and family Rhynochetidae, although a second species has been described from the fossil record. Measuring 55 cm (22 in) in length, it has pale grey plumage and bright red legs. Its nasal corns are a unique feature not shared with any other bird. Almost flightless, it spends its time on or near the ground, where it hunts its invertebrate prey and builds a nest of sticks on the forest floor. Both parents share incubation of a single egg and rearing the chick. It has proven vulnerable to introduced predators and is threatened with extinction.
Etymology
The name kagu is derived from the Melanesian names for the species. The species is variously known as the kavu or kagou in the Kanak languages, and as the cagou in French (also used as an alternative spelling in English).
Taxonomy and systematics
The generic name Rhynochetos and the family name Rhynochetidae are derived from the Greek ῥίς rhis meaning "nose" and χαίτη khaitē meaning "long hair", referring to its long, stiff hairs over the nostrils. The specific name jubatus is derived from the Latin iubātus meaning crested. The kagu's affinities are not well resolved. It was long one of the most enigmatic birds and in more recent times is usually affiliated with the Gruiformes. It was initially classed as a member of the clade Ardeae because of the presence of powder down, similarities in plumage colour and internal anatomy, the colour of the chicks and eggs, and the change in colouration of the chick as it grows. When seen as a gruiform, the kagu is generally considered related to the extinct adzebills from New Zealand and the sunbittern from Central and South America. Recent studies do indicate that the sunbittern is the closest living relative of the kagu. For example, Fain & Houde found these to be certainly sister taxa. They and the mesites did not group with traditional Gruiformes in their study, but instead with their proposed clade Metaves, which also includes the hoatzin, pigeons, nightjars, flamingos, tropicbirds, Apodiformes, sandgrouse, and grebes. The internal structure of this group was not well resolvable by their data, although later studies confirmed a close relationship between the kagu and sunbittern. The kagu and sunbittern, and possibly the adzebills, seem to form a distinct Gondwanan lineage of birds, either as one order or possibly more. Although the relationships between them and groups previously considered related, such as the mesites and the "core" Gruiformes are not yet resolved. The sunbittern and the mesites, notably, possess powder down, too, whereas the "core" Gruiformes do not. The ancestors of the kagu are believed to have diverged from the sunbittern in the Oligocene, 45 to 17 million years ago, and colonized New Caledonia 60 to 25 million years ago. In the absence of terrestrial predators, it eventually became flightless. While the kagu is the only living species in the Rhynochetidae, a larger species, the lowland kagu (Rhynochetos orarius), has been described from Holocene subfossil remains. The measurements of this species were 15% bigger than R. jubatus, with no overlap in measurements except those of the forelimbs. Given that the sites from which R. orarius remains have been recovered are all lowland sites, and that no fossils of R. jubatus have been found in these sites, the scientists who described the fossils have suggested that they represent highland and lowland species, respectively. R. orarius is one of many species to have become extinct in New Caledonia after the arrival of humans. The validity of the species has been questioned by some authors, but accepted by others.
Description
The kagu is a ground-living bird, 55 cm (22 in) in length. The weight can vary considerably by individual and by season, ranging from 700–1,100 g (25–39 oz). Its plumage is unusually bright for a bird of the forest floor; ash-grey and white coloured. Little sexual dimorphism is seen beyond a difference in the amount of barring in the primary feathers. It possesses powder down, which helps keep it dry and insulates it in the extremes of New Caledonia's tropical climate. The crest, which is used to display to other members of the species, is barely noticeable when at rest, but can be erected and fanned out. It is nearly flightless, using its wings for displays (its primary wing feathers are patterned) and moving quickly through the forest. It can also use them to glide when fleeing danger. The wings are not reduced in size like in most other flightless birds, and have a span around 77.5 cm (30.5 in), but they lack the musculature for flight. These wings are also used for a "broken-wing" display, a behaviour shared with its relative sunbittern, used to fake an injury and draw the attention of a predator away from its chick. It possesses bright red legs which are long and strong, enabling the bird to travel long distances and run quickly. It has large eyes, positioned so that they give good binocular vision, which is helpful in finding prey in the leaf litter and seeing in the gloom of the forest. It possesses nasal corns, structures covering its nostrils, which are a feature not shared by any other bird. These are presumed to prevent particles entering the nostrils when probing in soil during feeding. Another unique characteristic of the species is that it has only one-third as many red blood cells and three times more hemoglobin per red blood cell than is usual in birds.
… excerpt ends here. Continue reading the full article.
