White stork
The white stork is a large bird in the stork family, Ciconiidae. Its plumage is mainly white, with black on the bird's wings. Adults have long red legs and long pointed red beaks, and measure on average from beak tip to end of tail, with a wingspan. The two subspecies, which differ slightly in size, breed in Europe north to Finland, northwestern Africa, Palearctic east to southern Kazakhstan and southern Africa. The white stork is a long-distance migrant, wintering in Africa from tropical Sub-Saharan Africa to as far south as South Africa, or on the Indian subcontinent. When migrating between Europe and Africa, it avoids crossing the Mediterranean Sea and detours via the Levant in the east or the Strait of Gibraltar in the west, because the air thermals on which it depends for soaring do not form over water.
A carnivore, the white stork eats a wide range of animal prey, including insects, fish, amphibians, reptiles, small mammals and small birds. It takes most of its food from the ground, among low vegetation, and from shallow water. It is a monogamous breeder, and both members of the pair build a large stick nest, which may be used for several years. Each year the female can lay one clutch of usually four eggs, which hatch asynchronously 33–34 days after being laid. Both parents take turns incubating the eggs and both feed the young. The young leave the nest 58–64 days after hatching, and continue to be fed by the parents for a further 7–20 days.
The white stork has been rated as least concern by the International Union for Conservation of Nature. It benefited from human activities during the Middle Ages as woodland was cleared, but changes in farming methods and industrialisation saw it decline and disappear from parts of Europe in the 19th and early 20th centuries. Conservation and reintroduction programs across Europe have resulted in the white stork resuming breeding in the Netherlands, Belgium, Switzerland, Sweden and the United Kingdom. It has few natural predators, but may harbour several types of parasite; the plumage is home to chewing lice and feather mites, while the large nests maintain a diverse range of mesostigmatic mites. This conspicuous species has given rise to many legends across its range, of which the best-known is the story of babies being brought by storks.
Taxonomy and evolution
English naturalist Francis Willughby wrote about the white stork in the 17th century, having seen a drawing sent to him by Sir Thomas Browne of Norwich. He named it Ciconia alba. They noted they were occasional vagrants to England, blown there by storms. It was one of the many bird species originally described by Carl Linnaeus in the 10th edition of Systema Naturae, where it was given the binomial name of Ardea ciconia. It was reclassified to and designated the type species of the new genus Ciconia by Mathurin Jacques Brisson in 1760. Both the genus and specific epithet, cĭcōnia, are the Latin word for "stork".There are two subspecies:
- C. c. ciconia, the nominate subspecies described by Linnaeus in 1758, breeds from Europe to northwestern Africa and westernmost Asia and in southern Africa, and winters mainly in Africa south of the Sahara Desert, though some birds winter in India.
- C. c. asiatica, described by Russian naturalist Nikolai Severtzov in 1873, breeds in Turkestan and winters from Iran to India. It is slightly larger than the nominate subspecies.
A Ciconia fossil representing the distal end of a right humerus has been recovered from Miocene beds of Rusinga Island, Lake Victoria, Kenya. The 24–6 million year old fossil could have originated from either a white stork or a black stork, which are species of about the same size with very similar bone structures. The Middle Miocene beds of Maboko Island have yielded further remains.
Description
The white stork is a large bird. It has a length of, and a standing height of. The wingspan is and its weight is. Like all storks, it has long legs, a long neck and a long straight pointed beak. The sexes are identical in appearance, except that males are larger than females on average. The plumage is mainly white with black flight feathers and wing coverts; the black is caused by the pigment melanin. The breast feathers are long and shaggy forming a ruff which is used in some courtship displays. The irises are dull brown or grey, and the peri-orbital skin is black. The adult has a bright red beak and red legs, the colouration of which is derived from carotenoids in the diet. In parts of Spain, studies have shown that the pigment is based on astaxanthin obtained from an introduced species of crayfish and the bright red beak colours show up even in nestlings, in contrast to the duller beaks of young white storks elsewhere.As with other storks, the wings are long and broad, enabling the bird to soar. In flapping flight its wingbeats are slow and regular. It flies with its neck stretched forward and with its long legs extended well beyond the end of its short tail. It walks at a slow and steady pace with its neck upstretched. In contrast, it often hunches its head between its shoulders when resting. Moulting has not been extensively studied, but appears to take place throughout the year, with the primary flight feathers replaced over the breeding season.
Upon hatching, the young white stork is partly covered with short, sparse, whitish down feathers. This early down is replaced about a week later with a denser coat of woolly white down. By three weeks, the young bird acquires black scapulars and flight feathers. On hatching, the chick has pinkish legs, which turn to greyish-black as it ages. Its beak is black with a brownish tip. By the time it fledges, the juvenile bird's plumage is similar to that of the adult, though its black feathers are often tinged with brown, and its beak and legs are a duller brownish-red or orange. The beak is typically orange or red with a darker tip. The bills gain the adults' red colour the following summer, although the black tips persist in some individuals. Young storks adopt adult plumage by their second summer.
Similar species
Within its range, the white stork is distinctive when seen on the ground. The winter range of C. c. asiatica overlaps that of the Asian openbill, which has similar plumage but a different bill shape. When seen at a distance in flight, the white stork can be confused with several other species with similar underwing patterns, such as the yellow-billed stork, great white pelican and Egyptian vulture. The yellow-billed stork is identified by its black tail and a longer, slightly curved, yellow beak. The white stork also tends to be larger than the yellow-billed stork. The great white pelican has short legs that do not extend beyond its tail, and it flies with its neck retracted, keeping its head near to its stocky body, giving it a different flight profile. Pelicans also behave differently, soaring in orderly, synchronised flocks rather than in disorganised groups of individuals as the white stork does. The Egyptian vulture is much smaller, with a long wedge-shaped tail, shorter legs and a small yellow-tinged head on a short neck. The common crane, which can also look black and white in strong light, shows longer legs and a longer neck in flight.Distribution and habitat
The nominate race of the white stork has a wide although disjunct summer range across Europe, clustered in the Iberian Peninsula and North Africa in the west, and much of eastern and central Europe, with 25% of the world's population concentrated in Poland, as well as parts of western Asia. The asiatica population of about 1450 birds is restricted to a region in central Asia between the Aral Sea and Xinjiang in western China. The Xinjiang population is believed to have become extinct around 1980. Migration routes extend the range of this species into many parts of Africa and India. Some populations adhere to the eastern migration route, which passes across Israel into eastern and central Africa.In Africa the white stork may spend the winter in Tunisia, Morocco, Uganda, Angola, Zimbabwe, Djibouti, Botswana, Mozambique, Zambia, Eswatini, Gambia, Guinea, Algeria, and Ghana. A few records of breeding from South Africa have been known since 1933 at Calitzdorp, and about 10 birds have been known to breed since the 1990s around Bredasdorp. A small population of white storks winters in India and is thought to derive principally from the C. c. asiatica population as flocks of up to 200 birds have been observed on spring migration in the early 1900s through the Kurram Valley. However, birds ringed in Germany have been recovered in western and southern India. An atypical specimen with red orbital skin, a feature of the Oriental white stork, has been recorded and further study of the Indian population is required. North of the breeding range, it is a passage migrant or vagrant in Finland, Iceland, Ireland, Norway and Sweden, and west to the Azores and Madeira. Despite their geographical proximity, in Finland the species is rare, while in Estonia there are an estimated 5,000 breeding pairs. In recent years, the range has expanded into western Russia.
The white stork's preferred feeding grounds are grassy meadows, farmland and shallow wetlands. It avoids areas overgrown with tall grass and shrubs. In the Chernobyl area of northern Ukraine, white stork populations declined after the 1986 nuclear accident, as farmland was succeeded by tall grass and shrubs. In parts of Poland, poor natural foraging grounds have forced birds to seek food at rubbish dumps since 1999. White storks have also been reported foraging in rubbish dumps in the Middle East, North Africa and South Africa. Anthropogenic litter was found in the pellets of one third of breeding pairs in Poland, even though all pairs nested far from major dumps and landfills.
The white stork breeds in greater numbers in areas with open grasslands, particularly grassy areas which are wet or periodically flooded, and less in areas with taller vegetation cover such as forest and shrubland. They make use of grasslands, wetlands, and farmland on the wintering grounds in Africa. White storks were probably aided by human activities during the Middle Ages as woodland was cleared and new pastures and farmland were created, and they were found across much of Europe, breeding as far north as Sweden. The population in Sweden is believed to have been established in the 16th century, following the clearing of forests for agricultural purposes. Approximately 5,000 pairs were estimated to breed in the 18th century, but this number subsequently declined. The first accurate census in 1917 found 25 pairs, and the last pair failed to breed around 1955. A similar pattern was seen in Denmark where the white stork appears to have become established in the 15th century when forests were being replaced by farmland and meadows, followed by a rapid population increase in the next centuries and then a rapid decline due mainly to modern, high-intensity agriculture in the last 200 years. The white stork has been a rare visitor to the British Isles, with about 20 birds seen in Britain every year, and prior to 2020 there were no records of nesting since a pair nested atop St Giles High Kirk in Edinburgh, Scotland, in 1416. In 2020, a pair bred in the United Kingdom for the first time in over 600 years, as part of a re-introduction initiative in West Sussex called the White Stork Project.
A decline in population began in the 19th century due to industrialisation and changes in agricultural methods. White storks no longer nest in many countries, and the current strongholds of the western population are in Portugal, Spain, Ukraine and Poland. In the Iberian Peninsula, populations are concentrated in the southwest, and have also declined due to agricultural practices. A study published in 2005 found that the Podhale region in the uplands of southern Poland had seen an influx of white storks, which first bred there in 1931 and have nested at progressively higher altitudes since, reaching 890 m in 1999. The authors proposed that this was related to climate warming and the influx of other animals and plants to higher altitudes. White storks arriving in Poznań province in western Poland in spring to breed did so some 10 days earlier in the last twenty years of the 20th century than at the end of the 19th century.