In 2000 the World Conservation Union (IUCN) reported that, of the ninety-three species of Gruiformes examined, twenty-two species were already Extinct. In addition, one species, the Guam rail, exists only in captivity and is considered Extinct in the Wild. Four rail species are listed as Critically Endangered, facing an extremely high risk of extinction, while an additional eleven are listed as Endangered, facing a very high risk of extinction. Most endangered rails are threatened by introduced species of non-native mammals such as rats, cats, dogs, mongooses, pigs, snakes, and humans, as well as habitat destruction. The kagu is listed as Endangered, primarily because of the introduction of dogs onto the island of New Caledonia. Habitat destruction due to logging also plays a role. Three species of bustards are listed as Endangered: the great Indian bustard,
Flightlessness has evolved in many bird groups, but is particularly common among gruiforms. Rails that occupy island habitats appear to be especially likely to lose the ability to fly, in part because there are no natural predators on many island habitats. Flightless species have the advantage of no longer having to maintain the large avian flight muscles.
Bengal florican bustard, and lesser florican bustard. Bustard populations have been harmed by human hunting, habitat loss to agricultural and grazing land, and cattle and crows, which harm nests. Six additional bustard species are listed as Vulnerable. The cranes as a group are highly threatened, with one Critically Endangered species (the Siberian crane), two Endangered Species (the whooping crane and the Japanese crane), and six Vulnerable species, facing a high risk of extinction (Sarus crane, wattled crane, hooded crane, black-necked crane, blue crane, and white-naped crane).
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