Cagou
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 the family Rhynochetidae, although a second species has been described from the fossil record. Measuring 55 cm (21+1⁄2 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, as well as rearing the chick. It has proven vulnerable to introduced predators and is threatened with extinction.
The generic name Rhynochetos, and the clade name Rhynochetidae, are derived from the Greek rhis meaning nose and chetos meaning corn, referring to the corn-shaped flaps over the nostrils. The specific name jubatus is derived from the Latin iubātus meaning crested. 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).
The kagu is a ground-living bird, 55 cm (21+1⁄2 in) in length. The weight can vary considerably by individual and by season, ranging from 700 to 1,100 g (25–39 oz). Its plumage is unusually bright for a bird of the forest floor; ash-grey and white coloured. There is little sexual dimorphism 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 for moving quickly through the forest. It can also use them to glide when fleeing danger. The wings are not reduced in size like some other flightless birds, and have a span of around 77.5 cm (30+1⁄2 in), but they lack the musculature for flight. It possesses bright red legs which are long and strong, enabling the bird to travel long distances on foot 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.
The kagu is endemic to the forests and shrubland of New Caledonia. Within that island group it is restricted to the main island of Grande Terre. There is no evidence that it occurred on the Loyalty Islands, although fossil remains of the extinct lowland form R. orarius have been found on the Ile des Pines. The kagu is a habitat generalist and able to exist in a range of different forest types if sufficient prey is present, from rain forest to drier lowland forest. They are also able to feed in some drier shrubland associated with the island's ultrabasic rocks, although not in the poorest, low-prey shrubland of this type. They are also absent from areas where extensive ground cover makes foraging difficult, such as grassland or areas with high fern cover, but may pass through such areas to reach other foraging areas. The species has undergone some range contraction due to hunting and predation by introduced species. Its original, pre-human distribution, and the extent to which it and its sister species R. orarius coexisted in lowland areas of New Caledonia, is still not fully understood and awaits further research into the subfossil record.
Kagu are territorial, maintaining year-round territories of around 10–28 hectares (25–69 acres). Within the territory the pairs are solitary during the non-breeding season, and may have separate but overlapping foraging areas. Kagus make a range of different sounds, most commonly while duetting in the morning, each duet lasting about 15 minutes. The kagu's crest and wings are used in territorial displays towards other kagu, slightly different displays are used towards potential predators. Territorial disputes may be resolved by fighting using wings and bills, in the wild this seldom results in serious injuries.
The kagu is exclusively carnivorous, feeding on a variety of animals with annelid worms, snails and lizards being amongst the most important prey items. Also taken are larvae, spiders, centipedes and insects such as grasshoppers, bugs, and beetles. The majority of the diet is obtained from the leaf litter or soil, with other prey items found in vegetation, old logs and rocks. Sometimes kagus will hunt small animals in shallow water. Their hunting technique is to stand motionless on the ground or from an elevated perch, and silently watch for moving prey. They may stand on one foot and gently move the leaf litter with the other foot in order to flush prey. Having located prey they will move towards the prey and stand over it, ready to strike, or make a dash towards the prey from their watching location. If digging is required to obtain the prey this is done with the bill, the feet are not used to dig or scratch away debris.
Kagus are monogamous breeders, generally forming long-term pair bonds that are maintained for many years, even possibly life. Kagu can be long lived, with birds in captivity living for over 20 years. A single nesting attempt is made each year, although should the first nesting attempt fail a second attempt is made that year. A simple nest is constructed, which is little more than a heaped pile of leaves, although in some cases the egg may be laid directly on the ground. The nest is not concealed but is usually adjacent to a tree trunk, log or low vegetation. A single grey slightly blotched egg is laid which weighs 60–75 g. Incubation duties are shared by the parents. Each bird will incubate the egg for 24 hours, with the changeover occurring around noon each day. During each incubation stint the parent will remain on the egg the whole time except early in the morning, when the bird will briefly move away to call to its mate and occasionally forage quickly. The incubation period lasts for 33–37 days, which is long for the size of the egg. Offspring may remain in their parents' territory for many years after fledging, sometimes up to six years. These chicks do not help in incubating the eggs or raising the chicks, but nevertheless improve the breeding success of the parents. The older offspring do apparently help in territory defence, responding to playback of rivals and also participating in territorial fights, and it has been suggested that this should be treated as a form of cooperative breeding.
The kagu's initial decline was caused by subsistence hunting. The bird was trapped extensively for the European pet trade and for museums and zoos until it was afforded protection. It is threatened by introduced cats, pigs and dogs. New Caledonia lacked mammals (except for bats) before the arrival of humans, and many of its native species have been negatively affected by introduced mammals. Rats have a big impact on nestlings, accounting for 55% of nestling losses. Kagus also suffer from habitat loss caused by mining and forestry.
Concern was first raised about the future of the kagu in 1904. A visiting American scientist noted in 1948 that the extinction of the species was probable, and identified the many threats the species faced. The first concrete evidence of the impact of dogs came when a New Zealand researcher's study population was quickly exterminated by dogs in the 1990s, although suspicions about the importance of dogs and other predators had been voiced before this and dog control measures had been enacted in some areas in the 1980s. The kagu is listed as endangered (CITES I) and enjoys full protection in New Caledonia. It has been the subject of dedicated conservation efforts and is receptive to ex-situ conservation, breeding well in Nouméa Zoo. It is also prospering in Rivière Bleue Territorial Park, which has a pest-management programme and has been the site of releases into the wild of captive-bred birds.
Recent research has shown that naturally occurring heavy metals in the soil may affect Kagu through their food supply. Kagu in areas where soil levels of heavy metals were low laid more eggs and had higher numbers of fledglings, as well as having smaller home-ranges and higher body mass, than Kagu in areas where the soil was heavy-metal rich. It has therefore been suggested that Kagu conservation is likely to be more effective in areas where heavy-metal levels in the soil are low.
