GRUIFORM

Virginia rail (Rallus limicola) Sun bittern (Eurypyga helias) (order Gruiformes), any member of a rather loose assemblage of 12 families of birds that are generally agreed to be related but that differ widely in many aspects. They are an ancient group with a rich fossil history, but many are now restricted in range and few in number. Members of the order occur on every continent, but the only family with worldwide distribution is the Rallidae (rails [see photograph], gallinules, and coots), with 132 living species. Cranes (Gruidae) are found on every continent except South America, but many of the 15 species have small populations, some on the verge of extinction. The bustards (Otididae), with 23 species, have a wide distribution, limited to the Old World, but hunting pressures and modern agricultural methods have greatly reduced their numbers. The mesites (Mesitornithidae), however, are confined to Madagascar, and the kagu (Rhynochetus jubatus) to the island of New Caledonia. Other small families in the order contain the hemipodes, or button quails (Turnicidae), plains wanderer (Pedionomidae), limpkin (Aramidae), trumpeters (Psophiidae), finfoots (Heliornithidae), sun bittern (Eurypygidae; see photograph), and seriemas, or cariamas (Cariamidae). Although human impact on them is very great, gruiform birds, because of their scarcity, have a negligible impact on humans. With the possible exceptions of the sandhill crane (Grus canadensis), which descends on the grainfields of the Canadian prairies during the autumn migration, causing some crop damage, and the brolga, or Australian crane (Grus rubicundus), which causes similar damage in Queensland, no gruiform can be considered harmful to human interests; some of the larger species, in fact, are hunted for food or sport. order of birds (Gruiformes) containing 12 rather loosely related families. The most familiar members of the group are the cranes (family Gruidae), with 14 species represented on all continents but South America, and the rails, gallinules, and coots (Rallidae), with 132 species found throughout the world. The 23 species of bustards (Otidae) are limited to the Old World, as are the button quails, or hemipodes (Turnicidae). The limpkins (Aramidae), trumpeters (Psophiidae), sun bitterns (Eurypygidae), and seriemas, or cariamas (Cariamidae), are found in Central and South America. The finfoots (Heliornithidae) are found in tropical areas of Asia, Africa, and South America. Families with more limited distributions are the mesites (Mesitornithidae) of Madagascar, the plains wanderers (Pedionomidae) of Australia, and the kagus (Rhynochetidae) of New Caledonia. The gruiforms have the most complete fossil record of any bird order, and 14 extinct families are known. Though once a widespread and populous order, gruiforms are now on the decline, with many species, and even entire families, near extinction. Gruiforms are adapted to a wide variety of environments, and this is mirrored in the diversity of forms in the group. Their sizes range from the 6-inch (15-centimetre) button quail (Turnix) to the 5-foot (1.6-metre) high sarus crane (Grus antigone). The kori bustard (Otis kori) and the great bustard (O. tarda) are the heaviest flying birds in the world, reaching 40 pounds (18 kg) in weight. The plumage is usually various shades of brown and gray with white, but there are exceptions, such as the purple gallinule (Porphyrula martinica) with its purple neck, bronze-green back, and light blue shield. Bare skin on the face and neck of some species may be brightly coloured, as in the red faces of some cranes. Plumage is similar between the sexes except in the bustards, where males are more colourful, and the button quails, where the female is more highly coloured. Except in certain flightless rails, such as the takahes (Notornis mantelli) of New Zealand, and the nearly flightless mesites, the wings are rounded and generally long. A long, slender bill is typical, especially of the cranes, many rails, and limpkins (Aramus guarauna). The long legs are adapted for walking; a preference for this type of locomotion is found throughout the order. The toes themselves show diverse adaptations; in coots (Fulica) and finfoots the toes are lobed to aid in swimming; in rails and limpkins the long, narrow toes help in walking across lily pads and other aquatic plants; and in seriemas and bustards the short, strong toes aid in running on land. Gruiforms inhabit environments ranging from highly aquatic to arid. Finfoots, coots, limpkins, and rails prefer aquatic wetlands, while cranes nest in marshes but feed in open plains the rest of the year. Trumpeters, mesites, and kagus inhabit dense forests, while the rest of the orderthe bustards, seriemas, button quails, and plains wanderersprefers open grassland or plains. Most gruiforms are nonmigratory; only those from northern temperate areasmany cranes, some rails, and the Eurasian bustardsmigrate. However, some species of cranes perform spectacular migrations; for example, the sandhill cranes (Grus canadensis) often travel 6,440 km (4,000 miles) between their breeding and wintering grounds. Gruiforms are omnivorous but generally take a greater amount of animal food than vegetable food. However, the coots and gallinules take mostly aquatic vegetation. Finfoots live on mollusks, frogs, and fish, while the specialized limpkin eats mostly snails. The cranes take large amounts of animal food, including insects, crustaceans, amphibians, reptiles, and small mammals, and they will use their strong bills to dig into the ground for roots and bulbs. As a group, the gruiforms are probably best known for their impressive and graceful courtship displays, the most famous of which are the dances of the cranes. Cranes are monogamous and mate for life; to begin and maintain this pair bond, the birds regularly dance to each other. The pair circles while facing each other and then bow or bob their heads, increasing in speed until one or both jump into the air and begin to dance, sometimes tossing twigs or grass into the air as they leap. Rails maintain territories with various calls which also function to attract females; they may also perform courtship displays with the tail fanned and the wings raised. Most gruiforms nest on the ground, pulling together a simple nest of vegetation or twigs; bustards hardly form any nest, usually laying their eggs on the ground. Finfoots, the sun bittern, some trumpeters, and the mesites build twig nests in low trees. Clutch size varies from 1 egg in the kagu to more than 10 in some species of rails. In most families both parents incubate the eggs and care for the young; in bustards and trumpeters the female does all the work, and in button quails the males do. The young of most gruiforms leave the nest and follow their parents shortly after hatching. Additional reading Lawrence Walkinshaw, Cranes of the World (1973), provides comprehensive coverage; it is brought up to date by Paul A. Johnsgard, Cranes of the World (1983). Robert Porter Allen, The Whooping Crane (1952), is the classic monograph on this endangered species, with a brief descriptive and distributional treatment of the cranes of the world. Walkinshaw's The Sandhill Cranes (1949) contains detailed information on this species. Henry Eliot Howard, A Waterhen's Worlds (1940), is a monograph on the common gallinule or moorhen, with emphasis on behaviour, one of the early classics in ethology. S. Keith, C.W. Benson, and M.P. Stuart Irwin, The Genus Sarothrura (Aves, Rallidae), Bulletin of the American Museum of Natural History, vol. 143 (1970), is a study of this genus of African rails, with colour plates of the birds, diagrams of vocalizations, and a general treatment of rail voices. H.T. Hendrickson, A Comparative Study of the Egg White Proteins of Some Species of the Avian Order Gruiformes, Ibis, 3:8091 (1969), contains an exhaustive listing of the taxonomic characters for the order. G. Stuart Keith The Editors of the Encyclopdia Britannica