The true Cranes are birds of large size with long necks and legs, 19 or 20 cervical vertebras, the bill as long as the head or longer, and a depression which extends on each side half or more than half the length of the upper mandible, and contains the nostril shut in by a large membrane on the posterior side. Tail-feathers 12, primaries 11. Aftershaft present, but small; no fifth secondary; the lateral bare tracts extend some distance up the neck. Trachea passing into a hollow space between the bony walls of the sternal keel, and more or less convoluted ; furcula anchylosed to keel of sternum.
Cranes are generally grey or white in colour. They are in the main vegetable feeders, though they occasionally eat insects, reptiles, or fish. All have a loud trumpet-like call, the production of which is probably connected with the tracheal convolutions. The majority are migratory and gregarious. They breed on the ground, usually in marshy places, and lay two eggs, as a rule, in a rough nest of grass and rushes. They generally appear to pair for life, and indulge in most extraordinary dances during the nuptial season.
The Cranes have been divided into a large number of genera, some of which, distinguished solely by differences in the extent to which the head is feathered, are not here adopted.
Key to the Genera.
a. Crown naked or scantily clad with black hairs; feathers of fore neck not lengthened. ……………………Gnus, p. 185.
b. Head feathered throughout, feathers of fore neck lengthened ……………………ANTHROPOIDES, p. 190.