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{{Short description|Species of bird}}
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{{Speciesbox
| name = Kagu
| status = EN
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=BirdLife International |date=2019 |title=''Rhynochetos jubatus'' |volume=2019 |page=e.T22692211A156666402 |doi=10.2305/IUCN.UK.2019-3.RLTS.T22692211A156666402.en |access-date=19 November 2021}}</ref>
| status2 = CITES_A1 
 | status2_system = CITES 
 | status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>
| image = Kagu 0A2A2595.jpg
| image_alt = Bird (kagu) with pale grey plumage (lighter on underside), straight red bill and red legs
| taxon = Rhynochetos jubatus
| authority = [[Jules Verreaux|Verreaux, J]] & [[Marc Athanese Parfait Oeillet Des Murs|des Murs]], 1860
}}

{{Distinguish|text=the frontend to [[Libervia]] (software)}}

The '''kagu''' or '''cagou''' ('''''Rhynochetos jubatus''''') is a crested, long-legged, and bluish-grey bird [[endemism|endemic]] to the dense mountain forests of [[New Caledonia]]. It is the only surviving member of the genus ''[[Rhynochetos]]'' and the family [[Rhynochetidae]],<ref name="IOU">{{cite web |url=https://www.worldbirdnames.org/bow/loons/ |title=Kagu, Sunbittern, tropicbirds, loons, penguins |editor1-last=Gill | editor1-first=Frank |editor2-last=Donsker |editor2-first=David |editor3-last=Rasmussen |editor3-first=Pamela |year=2023 |work=World Bird List Version 13.1  |publisher=International Ornithologists' Union | access-date=8 April 2023 }}</ref> although a second species has been described from the [[fossil]] record.

Measuring {{convert|55|cm|in|frac=2|abbr=on}} 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 (biology)|egg]], as well as rearing the chick. It has proven vulnerable to introduced [[predator]]s and is threatened with extinction.

== Etymology ==
[[File:A pair of kagou birds (Rhinochaetus jubatus) with one displa Wellcome V0022346.jpg|thumb|Wood engraving of a pair, by F. J. Gauchard]]
The name kagu is derived from the [[Melanesian languages|Melanesian]] names for the species.<ref name="OED">{{cite web|title=Kagu|url=http://www.oed.com:80/Entry/102335|work=Oxford English Dictionary|publisher=Oxford University Press|access-date=11 January 2011}}</ref> The species is variously known as the ''kavu'' or ''kagou'' in the [[New Caledonian languages|Kanak languages]], and as the ''cagou'' in French (also used as an alternative spelling in English).<ref name ="HBW3"/>

== Taxonomy and systematics ==
[[File:Stavenn Eurypiga helias 00.jpg|thumb|The [[sunbittern]], a possible closest relative from Central and South America]]
The generic name ''Rhynochetos'', and the [[clade]] name Rhynochetidae, are derived from the [[Ancient Greek|Greek]] {{lang|el|ῥίς}} ''rhis'' meaning "nose" and {{lang|el|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.<ref>{{cite book | last = Jobling | first = James A. | title = A Dictionary of Scientific Bird Names | publisher = [[Oxford University Press]] | year = 1991 | location = Oxford | pages = 119, 335 | isbn = 978-0-19-854634-4 }}</ref>

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.<ref name="HBW3">{{cite book |editor-last1=del Hoyo |editor-first1=J. |editor-last2=Elliott |editor-first2=A. |editor-last3=Sargatal |editor-first3=J. |date=1996 |title=Handbook of the Birds of the World |volume=3: Hoatzin to Auks |url= |location= |publisher=Lynx Edicions |isbn=84-87334-20-2}}</ref>{{page needed|date=April 2023}}

When seen as a gruiform, the kagu is generally considered related to the extinct [[adzebill]]s from [[New Zealand]] and the [[sunbittern]] from [[Central America|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]].<ref>{{cite journal|author1=Fain, Matthew G. |author2=Houde, Peter |url=http://biology-web.nmsu.edu/houde/Parallel_radiations.pdf |doi=10.1554/04-235 |pmid=15612298 |title=Parallel Radiations in the Primary Clades of Birds |year=2004 |journal=Evolution |volume=58 |issue=11 |pages=2558–73 |s2cid=1296408 |url-status=dead |archive-url=https://web.archive.org/web/20130407204436/http://biology-web.nmsu.edu/houde/Parallel_radiations.pdf |archive-date=2013-04-07 }}</ref> They and the [[mesite]]s did not group with traditional Gruiformes in their study, but instead with their proposed [[clade]] [[Metaves]], which also includes the [[hoatzin]], [[pigeons]], [[Caprimulgiformes|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.<ref name=Hackett>Hackett, S.J. ''et al.'' (2008) A Phylogenomic Study of Birds Reveals Their Evolutionary History. ''Science'', 320(5884):1763–1768.</ref> 

The kagu and sunbittern, and possibly the [[adzebill]]s, seem to form a distinct [[Gondwana]]n 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. It is notable, however, that the sunbittern and the mesites 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.<ref name=":0">{{Cite journal |last1=Theuerkauf |first1=Jörn |last2=Rouys |first2=Sophie |last3=Bloc |first3=Henri |last4=Hunt |first4=Gavin R. |last5=Kuehn |first5=Ralph |last6=Gula |first6=Roman |date=February 2021 |title=Some like it odd: Long-term research reveals unusual behaviour in the flightless Kagu of New Caledonia |url=https://onlinelibrary.wiley.com/doi/10.1111/aec.12962 |journal=Austral Ecology |language=en |volume=46 |issue=1 |pages=151–154 |doi=10.1111/aec.12962 |s2cid=225105558 |issn=1442-9985}}</ref>

While the kagu is the only living species in the [[clade]] 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 ''Rhynochetos 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 that 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.<ref name ="Balouet">{{cite journal|last=Balouet|author-link=Jean Christophe Balouet|first=Jean C.|author2=Storrs L. Olson|title=Fossil birds from Late Quaternary deposits in New Caledonia|journal=Smithsonian Contributions to Zoology|year=1989|volume=469|issue=469|pages=28–32|url=http://si-pddr.si.edu/dspace/bitstream/10088/5164/2/SCtZ-0469-Lo_res.pdf|doi=10.5479/si.00810282.469|archive-url=https://web.archive.org/web/20120327043543/http://si-pddr.si.edu/dspace/bitstream/10088/5164/2/SCtZ-0469-Lo_res.pdf|archive-date=2012-03-27}}</ref> The validity of the species has been questioned by some authors,<ref name ="HBW3"/> but accepted by others.<ref name ="Steadman"/>

== Description ==
[[File:Juvenile kagu.jpg|thumb|right|The kagu possesses 'nasal corns', structures covering its nostrils, which are a feature not shared by any other bird. This bird is a juvenile, lacking the brightly coloured bill of the adult.]]
The kagu is a ground-living bird, {{convert|55|cm|in|frac=2|abbr=on}} in length. The weight can vary considerably by individual and by season, ranging from {{convert|700|to(-)|1100|g|oz|0|abbr=on}}. 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.<ref name ="HBW3"/>{{page needed|date=April 2023}} It possesses [[powder down]] which helps keep it dry and [[Thermal insulation|insulate]]s 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 [[Remiges|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 {{convert|77.5|cm|in|frac=4|abbr=on}}, but they lack the musculature for flight.<ref name ="HBW3"/>{{page needed|date=April 2023}}<ref name=":0" /> These wings are also used for a 'broken-wing' display, a behaviour shared with their relative sunbittern, used to fake an injury and draw the attention of a predator away from their chick. 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 cell]]s and three times more [[hemoglobin]] per red blood cell than is usual in birds.<ref name ="HBW3"/>{{page needed|date=April 2023}}

==Distribution and habitat==
The kagu is [[endemism|endemic]] to the [[forest]]s and [[shrubland]] of [[New Caledonia]]. Within that island group it is restricted to the main island of [[Grande Terre (New Caledonia)|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 [[Isle of Pines, New Caledonia|Ile des Pines]].<ref name ="Steadman">{{cite book | last = Steadman | first = David | author-link = David Steadman | title = Extinction and Biogeography in Tropical Pacific Birds | publisher = University of Chicago Press |location=Chicago | year = 2006 | page = 158 | isbn = 978-0-226-77142-7 }}</ref> The kagu is a habitat generalist and able to exist in a range of different forest types if sufficient prey is present, from [[New Caledonia rain forests|rain forest]] to drier lowland forest. They are also able to feed in some drier shrubland associated with the island's [[Ultramafic rock|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]].<ref name="HBW3"/> 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.<ref name ="Balouet"/>

==Behaviour and ecology==
Kagu are [[Territory (animal)|territorial]], maintaining year-round territories of around {{convert|10-28|ha|acre}}.<ref name="breed">{{cite journal |last=Salas |first=Michel |author2=Yves Letocart |year=1997 |title=Spatial Organisation and Breeding of Kagu ''Rhynochetos jubatus'' in Rivière Bleue Park, New Caledonia |journal=Emu |volume=97 |issue=2 |pages=97–107 |doi=10.1071/MU97013}}</ref>  They have a clan-based [[social organization]], with families composed of one breeding female and [[Polyandry in nature|one to three breeding males]]. Male offspring also help to defend their parents' territorial claims.<ref name=":0" /><ref name="coop">{{cite journal |last1=Theuerkauf |first1=Jörn |last2=Rouys |first2=Sophie |last3=Mériot |first3=Jean Marc |last4=Gula |first4=Roman |year=2009 |title=Group Territoriality as a form of Cooperative Breeding in the Flightless Kagu (''Rhynochetos jubatus'') of New Caledonia |journal=Auk |volume=126 |issue=2 |pages=371–375 |doi=10.1525/auk.2009.08092 |s2cid=85877849}} {{free access}} </ref> However the social organisation of kagu has been disrupted in recent years due to attacks by dogs and families. Cases where either the breeding male or female have been killed have led to non-fraternal polyandrous behaviour. Cooperative and unrelated polyandry is rare in birds, but has been seen in species such as the [[dunnock]] and the [[Tasmanian nativehen]]. 

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.<ref name="HBW3" /><ref name="coop" />

===Diet===
The kagu is exclusively carnivorous, feeding on a variety of animals with [[annelid|annelid worm]]s, [[snail]]s and [[lizard]]s being amongst the most important prey items.<ref name = HBW3/> Also taken are larvae, spiders, centipedes and insects such as [[grasshopper]]s, bugs, and [[beetle]]s. 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.<ref name = "HBW3"/>

===Breeding===
[[File:Rhynochetos jubatus MHNT.ZOO.2010.11.2.19.jpg|thumb| ''Rhynochetos jubatus'' egg - [[MHNT]]]]
Kagus are [[monogamy in animals|monogamous breeders]], generally forming long-term pair bonds that are maintained for many years, even possibly life.{{Disputed inline|date=June 2022}} Kagu can be long lived, with birds in captivity living for over 20 years.<ref name = "HBW3"/> A single nesting attempt is made each year, although should the first nesting attempt fail a second attempt is made that year.<ref name = "breed"/> A simple [[bird nest|nest]] is constructed, which is little more than a heaped pile of leaves, although in some cases the [[bird egg|egg]] may be laid directly on the ground. The [[bird nest|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. [[Avian incubation|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.<ref name = "HBW3"/> 

Offspring may remain in their parents' territory for many years after [[fledge|fledging]], sometimes up to six years.<ref name = "HBW3"/> 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 has also been observed adopting an unrelated chick, a behaviour more common in species with low reproductive output, high social organisation, and extensive parental care of the young, all traits shared by the kagu.<ref name=":0" />

==Status and conservation==
[[File:Kagu Rhynchetos jubatus detail.JPG|thumb|The current population of wild kagus is about 250–1000 birds, and the species is the focus of a decades-long conservation effort]]

The kagu's initial decline was caused by subsistence [[hunting]]. The bird was trapped extensively for the European pet trade<ref name=HBW3/> and for museums and zoos until it was afforded protection.<ref name="Warner">{{cite journal|last=Warner|first=Willard|title=The Present Status of the Kagu, ''Rhynochetos jubatus'', on New Caledonia|journal=Auk|year=1948|volume=65|issue=2|url = http://sora.unm.edu/sites/default/files/journals/auk/v065n02/p0287-p0288.pdf|pages=287–288|doi=10.2307/4080305|jstor=4080305}}</ref> It is threatened by introduced [[feral cat|cats]], [[pig]]s and [[dog]]s.<ref name="O'Neill">O'Neill, Thomas (2000) ''National Geographic'' '''197'''(5): pp. 54–75, page 74</ref> New Caledonia lacked mammals (except for bats) before the arrival of humans,<ref>Steadman D (2006). ''Extinction and Biogeography in Tropical Pacific Birds'', University of Chicago Press. {{ISBN|978-0-226-77142-7}}</ref> 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.<ref name = "Ekstrom">{{cite journal|author1=Ekstrom, J |author2=Jones, J |author3=Willis, J |author4=Tobias, J |author5=Dutson, G |author6=Barré, N |year=2002|title=New information on the distribution, status and conservation of terrestrial bird species in Grande Terre, New Caledonia|journal=[[Emu (journal)|Emu]]|doi=10.1071/MU01004|volume=102|issue=2|pages=197|s2cid=85342052 }}</ref> Kagus also suffer from [[habitat loss]] caused by [[mining]] and [[forestry]].

Concern was first raised about the future of the kagu in 1904.<ref name="emu1904">{{cite journal|last1=Campbell|title= The kagu of New Caledonia|journal=Emu|year=1904|volume=4|issue=4|pages=166–168 |doi=10.1071/MU904166|first1=A.J. |url= https://zenodo.org/record/2451173}}</ref> A visiting American scientist noted in 1948 that the extinction of the species was probable, and identified the many threats the species faced.<ref name="Warner"/> 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,<ref>{{cite journal|author=Hunt, G.R.|author2=Hay, R.|author3=Veltman, C.J.|name-list-style=amp |year=1996|title=Multiple kagu ''Rhynochetos jubatus'' deaths caused by dog attacks at a high altitude study site on Pic Ningua, New Caledonia|journal=Bird Conservation International|volume=6|pages= 295–306|doi=10.1017/S0959270900001775|issue=4|doi-access=free}}</ref> 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.<ref>{{cite journal|author=Tolmé, P |year=2003|url=http://www.nwf.org/nationalwildlife/article.cfm?issueID=64&articleID=835 |title=Gray Ghosts of the Cloud Forest|journal=National Wildlife|volume=41|issue=6|archive-url=https://web.archive.org/web/20040218183313/http://www.nwf.org/nationalwildlife/article.cfm?issueID=64&articleID=835|archive-date=2004-02-18}}</ref> The kagu is listed as [[endangered]] ([[CITES]] I) and enjoys full protection in New Caledonia. It has been the subject of dedicated [[Conservation movement|conservation]] efforts and is receptive to [[ex-situ conservation]], breeding well in [[Nouméa Zoo]]. It is also prospering in [[Rivière Bleue Territorial Park]],<ref>also known as Rivière Bleue Provincial Park and Rivière Bleue National Park</ref> which has a [[pest (animal)|pest]]-management programme and has been the site of releases into the wild of captive-bred birds.<ref name="O'Neill"/>

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.<ref>{{cite journal |author1=Theuerkauf, J.|author2=Haneda, T.| author3=Okahisa, Y. |author4=Sato, N. J.| author5=Rouys, S.|author6=Bloc, H. |author7=Ueda, K.| author8=Watanabe, I. |author9=Kuehn, R.| author10=Gula, R. |  year=2017| title=Elevated concentrations of naturally occurring heavy metals inversely correlate with reproductive output and body mass of the Kagu ''Rhynochetos jubatus''| journal=Ibis| volume=159| pages=580–587| doi=10.1111/ibi.12474| issue=3}}</ref>

==Relationship with humans==
The kagu had an important role in the traditional lives of the [[Kanak people|Kanak]] tribes of New Caledonia. Among the tribes found in the vicinity of [[Hienghène]] in the north of Grande Terre, its name was given to people, its crest was used in the head-dresses of chiefs, and its calls were incorporated into war dances and considered messages to be interpreted by the chiefs. Kanaks in the vicinity of [[Houaïlou]] referred to the species as the "ghost of the forest."<ref name="HBW3"/>

The species was not discovered by Europeans until the French colonisation of New Caledonia in 1852 and was not described until a specimen was taken to the [[Colonial Exhibition]] in Paris in 1860.<ref name="emu1904"/> This led to a surge in scientific interest in the species, which resulted in many birds being trapped for museums and zoos. The species was also trapped for food and was considered a delicacy by European colonisers. It was also fashionable to own kagus as pets. A campaign was run from 1977–1982 to phase out the pet trade in kagus. Today, the kagu is considered very important in New Caledonia; it is a high-profile [[endemic (ecology)|endemic]] emblem for the territory. Its distinctive song used to be played to the nation every night as the island's TV station signed off the air. Its survival is considered important for the territory's economy and image.<ref name="HBW3"/>

==See also==
* [[Biodiversity of New Caledonia]]

==References==
{{Reflist|35em}}

==External links==
{{Commons category|Rhynochetidae}}
* [http://www.birdlife.org/datazone/speciesfactsheet.php?id=2808 BirdLife Species Factsheet.]
* ARKive - [https://web.archive.org/web/20060322170708/http://www.arkive.org/species/GES/birds/Rhynochetos_jubatus/ images and movies of the kagu (''Rhynochetos jubatus'')]
* [https://search.macaulaylibrary.org/catalog?taxonCode=kagu1 Kagu videos, photos & sounds] on the Internet Bird Collection
* [http://www.sandiegozoo.org/animalbytes/t-kagu.html Kagu information, photos & sounds] at San Diego Zoo Animal Bytes.

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[[Category:Endemic birds of New Caledonia]]
[[Category:Flightless birds]]
[[Category:Higher-level bird taxa restricted to the Australasia-Pacific region]]
[[Category:Endangered fauna of Oceania]]
[[Category:Birds described in 1860]]