Crane (bird)


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. 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.

Description

Cranes are very large birds, often considered the world's tallest flying birds. They range in size from the demoiselle crane, which measures in length, to the sarus crane, which can be up to, although the heaviest is the red-crowned crane, which can weigh 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 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 also daub their feathers with mud which some observers suspect helps them to hide while nesting.
File:SarusTrachea.jpg|thumb|The long coiled trachea that produces the trumpeting calls of cranes
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.

Taxonomy and systematics

The family name Gruidae comes from the genus Grus, this genus name is obtained from the epithet of the common crane which was named Ardea grus by Carl Linnaeus, from the Latin word grus meaning "crane".
The 15 living species of cranes are placed in four genera. A molecular phylogenetic study published in 2010 found that the genus Grus, as then defined, was polyphyletic. In the resulting rearrangement to create monophyletic genera, the Siberian crane was moved to the resurrected monotypic genus Leucogeranus, while the sandhill crane, the white-naped crane, the sarus crane, and the brolga were moved to the resurrected genus Antigone. Some authorities recognize the additional genera Anthropoides and Bugeranus.
The following cladogram is based on a molecular phylogenetic study by Carey Krajewski and collaborators that was published in 2010.

Evolution

The fossil record of cranes is incomplete. Apparently, the subfamilies were well distinct by the Late Eocene. The present genera are apparently some 20 mya old. Biogeography of known fossil and the living taxa of cranes suggests that the group is probably of Old World origin. The extant diversity at the genus level is centered on Africa, although no fossil record exists from there. On the other hand, it is peculiar that numerous fossils of Ciconiiformes are documented from there; these birds presumably shared much of their habitat with cranes back then already. Cranes are sister taxa to Eogruidae, a lineage of flightless birds; as predicted by the fossil record of true cranes, eogruids were native to the Old World. A species of true crane, Antigone cubensis, has similarly become flightless and ratite-like.
File:Ergilornis.jpg|thumb|upright|250px|Eogruidae is an extinct lineage of mostly flightless stem-cranes. Pictured is the two-toed Ergilornis.
Fossil genera are tentatively assigned to the present-day subfamilies:
Gruinae
  • Palaeogrus
  • Pliogrus
  • Camusia
  • "Grus" conferta
Sometimes considered Balearicinae
  • Geranopsis
  • Anserpica
Sometimes considered Gruidae incertae sedis
  • Eobalearica
  • Probalearica – A nomen dubium?
  • ''Aramornis''

    Distribution and habitat

The cranes have a cosmopolitan distribution, occurring across most of the world continents. They are absent from Antarctica and, mysteriously, South America. East Asia has the highest crane diversity, with eight species, followed by Africa, which is home to five resident species and wintering populations of a sixth. Australia, Europe, and North America have two regularly occurring species each. Of the four crane genera, Balearica is restricted to Africa, and Leucogeranus is restricted to Asia; the other two genera, Grus and Antigone, are both widespread.
Many species of cranes are dependent on wetlands and grasslands, and most species nest in shallow wetlands. Some species nest in wetlands, but move their chicks up onto grasslands or uplands to feed, whereas others remain in wetlands for the entirety of the breeding season. Even the demoiselle crane and blue crane, which may nest and feed in grasslands, require wetlands for roosting at night. The Sarus Crane in south Asia is unique in having a significant breeding population using agricultural fields to breed in areas alongside very high density of humans and intensive farming, largely due to the positive attitudes of farmers towards the cranes. In Australia, the Brolga occurs in the breeding areas of Sarus Cranes in Queensland state, and they achieve sympatry by using different habitats. Sarus Cranes in Queensland largely live in Eucalyptus-dominated riverine, while most Brolgas use non-wooded regional ecosystems that include vast grassland habitats. The only two species that do not always roost in wetlands are the two African crowned cranes, which are the only cranes to roost in trees.
Some crane species are sedentary, remaining in the same area throughout the year, while others are highly migratory, traveling thousands of kilometres each year from their breeding sites. A few species like Sarus Cranes have both migratory and sedentary populations, and healthy sedentary populations have a large proportion of cranes that are not territorial, breeding pairs.

Behaviour and ecology

The cranes are diurnal birds that vary in their sociality by season and location. During the breeding season, they are territorial and usually remain on their territory all the time. In contrast in the non-breeding season, they tend to be gregarious, forming large flocks to roost, socialize, and in some species feed. Sarus Crane breeding pairs maintain territories throughout the year in south Asia, and non-breeding birds live in flocks that can also be seen throughout the year. Large aggregations of cranes likely increase safety for individual cranes when resting and flying and also increase chances for young unmated birds to meet partners.

Calls and communication

Cranes are highly vocal and have several specialized calls. The vocabulary begins soon after hatching with low, purring calls for maintaining contact with their parents, as well as food-begging calls. Other calls used as chicks include alarm calls and "flight intention" calls, both of which are maintained into adulthood. Cranes are noticed the most due to their loud duet calls that can be used to distinguish individual pairs. Sarus crane trios produce synchronized unison calls called "triets" whose structure is identical to duets of normal pairs, but have a lower frequency.

Feeding

The cranes consume a wide range of food, both animal and plant matter. When feeding on land, they consume seeds, leaves, nuts and acorns, berries, fruit, insects, worms, snails, small reptiles, mammals, and birds. In wetlands and agriculture fields, roots, rhizomes, tubers, and other parts of emergent plants, other molluscs, small fish, eggs of birds and amphibians are also consumed, as well. The exact composition of the diet varies by location, season, and availability. Within the wide range of items consumed, some patterns are suggested but require specific investigation to confirm; the shorter-billed species usually feed in drier uplands, while the longer-billed species feed in wetlands.
Cranes employ different foraging techniques for different food types and in different habitats. Tubers and rhizomes are dug for and a crane digging for them remains in place for some time digging and then expanding a hole to prise them out of the soil. In contrast both to this and the stationary wait and watch hunting methods employed by many herons, they forage for insects and animal prey by slowly moving forwards with their heads lowered and probing with their bills.
Where more than one species of cranes exists in a locality, each species adopts separate niches to minimise competition. At one important lake in Jiangxi Province in China, the Siberian cranes feed on the mudflats and in shallow water, the white-naped cranes on the wetland borders, the hooded cranes on sedge meadows, and the last two species also feed on the agricultural fields along with the common cranes. In Australia, where Sarus Cranes live alongside Brolgas, they have different diets: Sarus Cranes' diet consisted of diverse vegetation, while Brolga diet spanned a much wider range of trophic levels. Some crane species such as the Common/ Eurasian crane use a kleptoparasitic strategy to recover from temporary reductions in feeding rate, particularly when the rate is below the threshold of intake necessary for survival. Accumulated intake of during daytime shows a typical anti-sigmoid shape, with greatest increases of intake after dawn and before dusk.