Description
The cranes are large to very large birds, including the world's tallest flying bird. 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. 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 on average males tend to be slightly larger than females.
The plumage of the cranes varies by habitat. Species inhabiting vast open wetlands tend to have more white in the 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 to further hide while nesting. Most species of crane have some areas of bare skin on the face, the only two exceptions are the Blue and Demoiselle Cranes. This skin is used in communication with other cranes, and can be expanded by contracting and relaxing muscles, and change the intensity of colour. Feathers on the head can be moved and erected in the Blue, Wattled and Demoiselle Cranes for signalling as well. 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 is longer and penetrates 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.
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