CRANES, RAILS, AND RELATIVES: Gruiformes

PHYSICAL CHARACTERISTICS

Gruiforms, birds of the order Gruiformes, vary greatly in size. The smallest species, the American black rail, is only 4.7 inches (12 centimeters) high, whereas the Sarus crane, at 5.8 feet (176 centimeters), is the tallest flying bird. Weights in the group also vary tremendously. The American black rail weighs in at only 8 ounces (20 grams), while kori bustards and great bustards have been known to reach weights of more than 40 pounds (18 kilograms), making them among the heaviest flying birds.

Most species of Gruiformes are primarily black, gray, or brown in color, and many species have streaked markings. However, there are some exceptions, including the sunbittern and some rails and cranes. Rails are sometimes greenish or purplish in color. Cranes have black or white feathers, often with distinctive patches of red skin on the head and neck. The sunbittern is a particularly colorful gruiform, with large black and red "eyespots" on its wings—these spots resemble the eyes of a much larger animal and help scare off potential predators.

Bill shape also varies among the gruiforms. Cranes have narrow, medium-length bills that they use to search for invertebrates in soft mud. Trumpeters, which search for food on rainforest floors, have short bills resembling those of chickens. The limpkin has an extremely unusual bill, which bends to the right at its tip. The limpkin's bill is adapted to feeding on apple snails, its primary food.

GEOGRAPHIC RANGE

Gruiformes as a group are found on all the continents except Antarctica, although most gruiform families have a more limited distribution. The kagu is found exclusively on the island of New Caledonia, off the coast of Australia in the Pacific Ocean. Buttonquails are found in portions of Europe, Africa, Asia, and Australia. Mesites are found in Madagascar. Trumpeters are found in the Amazon basin in the northern part of South America. Seriemas are found in central and eastern South America. The sunbittern is found in Central America and South America. The limpkin is found in Central America and South America, as well as parts of Florida and Mexico. Bustards inhabit portions of Africa, southern Europe, south and Southeast Asia, New Guinea, and Australia. Sungrebes are found in Central America, South America, Africa, and south and Southeast Asia. Cranes are found on all continents except Antarctica and South America, although Asia and Africa are particularly rich in species. Rails, gallinules, and coots are also found worldwide.

HABITAT

The Gruiformes as a group occupy diverse habitats. Sungrebes are aquatic, and generally live in marshes, lakes, and streams. Sunbitterns live in rainforests and swamps. Limpkins live in marshes or swamps. Cranes live in freshwater and marine wetlands. Rails live near swamps, marshes, and lakes. Trumpeters live in tropical rainforests. Kagus inhabit forest-lands. Mesites live in a wide variety of habitats, including rainforest, deciduous forest, and dry scrubland. Seriemas occupy grassland habitats. Bustards live in brush and scrub habitats as well as open grassland.

DIET

As a group, the Gruiformes eat a wide variety of plant and animal matter. Sungrebes eat small insects and other aquatic animals, as well as seeds and leaves. Sunbitterns eat insects, small fish, and crustaceans. The limpkin's primary prey is apple snails, but they also eat insects and seeds. Cranes have a diverse diet, eating seeds and other vegetable and animal matter. Rails also eat a diverse diet of animal and plant matter. Trumpeters eat fruits, berries, seeds, and other plant matter. The kagu eats insects, worms, small frogs, and mollusks. Mesites eat fruit, seeds, and insects. Seriemas eat insects, small reptiles, mammals, and some plant matter. Bustards eat seeds, insects, and other small animals.

BEHAVIOR AND REPRODUCTION

Sunbitterns, limpkins, sungrebes, kagus, and rails tend to be solitary, living alone. Some species are territorial, that is, individuals defend a territory against other members of the same species. Other Gruiformes, however, such as seriemas and mesites, are frequently found in male-female pairs. Finally, some species of bustards, trumpeters, and cranes occur in flocks and can be highly social.

Gruiforms vary from highly able fliers to flightless species. Many cranes, for example, carry out long migrations between their breeding grounds and wintering grounds. Other Gruiformes are reluctant to fly, and flightlessness has in fact evolved many times in the group, particularly among the rails.

Reproductive behavior also varies within the Gruiformes. Cranes are monogamous (muh-NAH-guh-mus)—that is, each male mates with a single female and both parents are involved in building the nest, incubating the eggs, and caring for the chicks once they hatch. In order to strengthen the bond between the pair, cranes engage in elaborate "dances" in which they leap, extend their wings, and bob their heads. Mated crane pairs also sing, or trumpet, together. Crane pairs typically stay together all year round, rather than just during the breeding season, and some mate for life. At the other extreme in reproductive behavior, bustard males mate with as many females as they can. Females build nests, incubate eggs, and raise young on their own, without assistance from the male.

CRANES, RAILS, RELATIVES, AND PEOPLE

Gruiforms have been important to humans for a variety of reasons. Many species currently or traditionally have been hunted for food. Mesites are hunted for food in their habitats in Madagascar. Many species of buttonquails are also hunted for food, although this became illegal in many countries in 2001. Several species of buttonquails are now farmed as domestic livestock. In addition, some buttonquails play a role in the religious ceremonies of the Australian aborigines, and one species, the barred buttonquail, is used as a fighting bird. Cranes are symbols of good luck in many parts of the world, appearing in some cases as national symbols or on coins. The whooping crane is frequently used as a symbol of conservation because of the extensive effort devoted to saving it from extinction. Limpkins were once hunted for meat. Today their calls represent a significant part of the culture of some aboriginal peoples. Kagus have always been hunted for meat, their feathers have been used for decoration by indigenous cultures, and kagu songs were imitated in war dances. In addition, kagus were once kept as pets by Europeans. They now frequently appear as a symbol of New Caledonia. Rails have been hunted for food and sport throughout the world, and rail eggs are often eaten as well. Some species have also served as fighting birds, incubators of chicken eggs, or as pets. Sunbitterns have been kept as pets. Trumpeters have also been kept as pets or used to guard chicken coops from snakes. They have also been hunted for food. Seriemas are sometimes used to guard chicken coops, again because they kill large numbers of snakes. Bustards make an important contribution to human agriculture by eating large numbers of insect pests. Some bustards are also hunted, particularly in North Africa and Cambodia, in some cases with the use of trained falcons. Finally, many species of Gruiformes attract birdwatchers and ecotourists throughout the world.

FLIGHTLESSNESS

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.

CONSERVATION STATUS

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, 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).

FOR MORE INFORMATION

Books:

del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 3, Hoatzin to Auks. Barcelona: Lynx Edicions, 1996.

Matthiessen, Peter. The Birds of Heaven: Travels with Cranes. New York: North Point Press, 2001.

Perrins, Christopher, ed. Firefly Encyclopedia of Birds. Buffalo, NY: Firefly Books, 2003.

Taylor, P. B., B. Taylor, and B. van Perlo. Rails: A Guide to the Rails, Crakes, Gallinules, and Coots of the World. New Haven, CT: Yale University Press, 1998.

Web sites:

"Birds of the World." Bird Families of the World, Cornell University. http://www.es.cornell.edu/winkler/botw/families.htm (accessed on March 25, 2004).

The Internet Bird Collection. http://www.hbw.com/ibc/phtml/families.phtml (accessed on March 25, 2004).

"Order Gruiformes (Cranes, Coots, and Rails)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/classification/gruiformes.html (accessed on March 25, 2004).