Cranes are a type of large bird with long legs and necks in the biological family Gruidae of the order Gruiformes. The family has 15 species placed in four genera which are Antigone, Balearica, Leucogeranus, and Grus.They are large birds with long necks and legs, a tapering form, and long secondary feathers on the wing that project over the tail. Most species have muted gray or white plumages, marked with black, and red bare patches on the face, but the crowned cranes of the genus Balearica have vibrantly-coloured wings and golden "crowns" of feathers. Cranes fly with their necks extended outwards instead of bent into an S-shape and their long legs outstretched.
Cranes live on most continents, with the exception of Antarctica and South America. Some species and populations of cranes migrate over long distances; others do not migrate at all. Cranes are solitary during the breeding season, occurring in pairs, but during the non-breeding season, most species are gregarious, forming large flocks where their numbers are sufficient.
They are opportunistic feeders that change their diets according to the season and their own nutrient requirements.[citation needed] They eat a range of items from small rodents, eggs of birds, fish, amphibians, and insects to grain and berries. Cranes construct platform nests in shallow water, and typically lay a clutch of two eggs at a time. Both parents help to rear the young, which remain with them until the next breeding season. Most species of cranes have been affected by human activities and are at the least classified as threatened, if not critically endangered.The plight of the whooping cranes of North America inspired some of the first US legislation to protect endangered species.
The bare area of skin on the face of a sandhill crane can change colour or even expand in area when the bird is excited.
Cranes are very large birds, often considered the world's tallest flying birds. They range in size from the demoiselle crane, which measures 90 cm (35 in) in length, to the sarus crane, which can be up to 176 cm (69 in), although the heaviest is the red-crowned crane, which can weigh 12 kg (26 lb) prior to migrating.[citation needed] They are long-legged and long-necked birds with streamlined bodies and large, rounded wings. The males and females do not vary in external appearance, but males tend to be slightly larger than females.
The plumage of cranes varies by habitat. Species inhabiting vast, open wetlands tend to have more white in their plumage than do species that inhabit smaller wetlands or forested habitats, which tend to be more grey. These white species are also generally larger. The smaller size and colour of the forest species is thought to help them maintain a less conspicuous profile while nesting; two of these species (the common and sandhill cranes) also daub their feathers with mud which some observers suspect helps them to hide while nesting.
The long coiled trachea that produces the trumpeting calls of cranes (sarus crane, Antigone antigone)
Most crane species have bare patches of skin on their heads and can expand the patches in order to communicate aggression. Species lacking these bare patches use specialized feather tufts to signal similar information.
Also important to communication is the position and length of the trachea. In the two crowned cranes, the trachea is shorter and only slightly impressed upon the bone of the sternum, whereas the trachea of the other species are longer and penetrate the sternum. In some species, the entire sternum is fused to the bony plates of the trachea, and this helps amplify the crane's calls, allowing them to carry for several kilometres