Kagu close relationship between the kagu and sunbittern. The kagu and sunbittern, and possibly the adzebills, seem to form a distinct Gondwanan lineage of birds, possibly one order, possibly more, though 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. 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
Kagu 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 (22–62 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