The common crane (Grus grus), also known as the Eurasian crane, is a bird of the family Gruidae, the cranes. A medium-sized species, it is the only crane commonly found in Europe besides the demoiselle crane (Grus virgo) and the Siberian crane (Leucogeranus leucogeranus) that only are regular in the far eastern part of the continent. Along with the sandhill crane (Antigone canadensis), demoiselle crane and the brolga (Antigone rubicunda), it is one of only four crane species not currently classified as threatened with extinction or conservation dependent on the species level. Despite the species' large numbers, local extinctions and extirpations have taken place in part of its range, and an ongoing reintroduction project is underway in the United Kingdom.

Taxonomy

The first formal description of the common crane was by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Ardea grus. The current genus Grus was erected by the French zoologist Mathurin Jacques Brisson in 1760. Grus is the Latin word for a "crane". The species is considered to be monotypic: no subspecies are recognised.

Description

The common crane is a large, stately bird and a medium-sized crane. It is long with a wingspan. The body weight can range from , with the nominate subspecies averaging around and the eastern subspecies (G. g. lilfordi) averaging . Among standard measurements, the wing chord is long, the tarsus is and the exposed culmen is .

Males are slightly heavier and larger than females, with weight showing the largest sexual size dimorphism, followed by wing, central toe, and head length in adults and juveniles.

The species is a migrant and common cranes that breed in Europe predominantly winter in Portugal, Spain and northern Africa. Common cranes that breed in far eastern Europe, including European Russia, winter in the river valleys of Sudan, Ethiopia, Tunisia and Eritrea with smaller numbers in Turkey, northern Israel, Iraq and parts of Iran. The third major wintering region, primarily used by those breeding in central Russia, is in the northern half of the Indian subcontinent, including Pakistan. Minimal wintering also occurs in Burma, Vietnam and Thailand. Lastly, the easternmost breeders winter in eastern China, where they are often the most common crane. Migrating flocks fly in a "V" formation.

It is a rare visitor to Japan and Korea, mostly blown over from the Chinese wintering population, and is a rare vagrant to western North America, where birds are occasionally seen with flocks of migrating sandhill cranes.

Habitat

thumb|Common cranes in [[Osmussaar, Estonia. Wetlands are preferred habitats for the cranes.]]

In Europe, the common crane predominantly breeds in boreal and taiga forest and mixed forests, from an elevation of sea-level to . In northern climes, it breeds in treeless moors, on bogs, or on dwarf heather habitats, usually where small lakes or pools are also found. In Sweden, breeders are usually found in small, swampy openings amongst pine forests, while in Germany, marshy wetlands are used. Breeding habitat used in Russia are similar, though they can be found nesting in less likely habitat such as steppe and even semi-desert, so long as water is near. Primarily, the largest number of common cranes are found breeding in wooded swamps, bogs and wetlands and seem to require quiet, peaceful environs with minimal human interference. They occur at low density as breeders even where common, typically ranging from 1 to 5 pairs per .

In winter, this species moves to flooded areas, shallow sheltered bays, and swampy meadows. During the flightless moulting period there is a need for shallow waters or high reed cover for concealment. Later, after the migration period, the birds winter regularly in open country, often on cultivated lands and sometimes also in savanna-like areas, for example on the Iberian Peninsula.

Animal foods become more important during the summer breeding season and may be the primary food source at that time of year, especially while regurgitating to young. Their animal foods are insects, especially dragonflies, and also snails, earthworms, crabs, spiders, millipedes, woodlice, amphibians, rodents, and small birds.

Common cranes may either forage on land or in shallow water, probing around with their bills for any edible organism. Although crops may locally be damaged by the species, they mostly consume waste grain in winter from previously harvested fields and so actually benefit farmers by cleaning fields for use in the following year.

Sociality

The common crane is a fairly social bird while not breeding. Flocks of up to 400 birds may be seen flying together during migration. Staging sites, where migrating birds gather to rest and feed in the middle of their migration, may witness thousands of cranes gathering at once. However, the flocks of the species are not stable social units but rather groups that ensure greater safety in numbers and collectively draw each other's attention to ideal foraging and roosting sites.

Cranes 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. The crane has been known to counterattack eagles both on the land and in mid-flight, using their bill as a weapon and kicking with their feet. The carrion crow (Corvus corone) is locally a successful predator of common cranes' eggs, trickily using distraction displays to steal them. Other species of Corvus may also cause some loss of eggs, with common ravens (Corvus corax) also taking some small chicks.) and Sweden ( 30,000 pairs in 2012). On the fringes of its range, it has often become rare or even been extirpated, but in several European countries this trend has been reversed and overall the European population is increasing. Norway had 3–5,000 pairs in 2015 and Estonia had 5,800 pairs in 1999, with both increasing. The German breeding population increased from 700 pairs in 1978 to more than 10,000 pairs in 2017, which is still a fraction of the size of the numbers that once bred in the country. After having disappeared as a breeding bird decades earlier, the species began breeding again in France in 2000 and in 2017 there were more than 20 pairs. In Denmark, the common crane returned as a breeder in 1953, about a century after it had disappeared. Numbers remained extremely low, less than 5 pairs, until the 1990s when a rapid increase began; in 2022 there were at least 750 pairs in Denmark. In the Netherlands, the species disappeared as a breeding bird centuries ago, but it returned in 2001 and by 2020 there were about 40 pairs in the country. The common crane returned to the Czech Republic as a breeder in 1981 and by 2004 it had increased to 35 pairs. In 2009, the species again began to breed in Slovakia, Although large numbers winter in Spain, the last breeding in the country had been in 1954. In 2017, a pair that had been released after being rehabilitated bred in Spain. It was extirpated as a breeder from Italy around 1920 and Hungary by 1952, and it also used to breed in the Balkans; significant numbers still pass through these countries during migration.

In the United Kingdom, the common crane became extirpated in the 17th century, but a small and increasing population now breeds again in the Norfolk Broads In 2021, the British population had increased to 72 pairs.

The main threat to the species and the primary reason for its decline comes from habitat loss and degradation, as a result of dam construction, urbanisation, agricultural expansion,

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  • Eurasian Crane at the International Crane Foundation
  • Observing cranes without disturbing them