The white stork (Ciconia ciconia) 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 100–115 cm (39–45 in) from beak tip to end of tail, with a 155–215 cm (61–85 in) wingspan. The two subspecies, which differ slightly in size, breed in Europe (north to Finland), northwestern Africa, southwestern Asia (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, but does not pair for life. 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 (IUCN). 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.
Description & appearance
The white stork is a large bird. It has a length of 100–115 cm (39–45 in), and a standing height of 100–125 cm (39–49 in). The wingspan is 155–215 cm (61–85 in) and its weight is 2.3–4.5 kg (5.1–9.9 lb). 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 (Procambarus clarkii) 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.
The white stork is a gregarious bird; flocks of thousands of individuals have been recorded on migration routes and at wintering areas in Africa. Non-breeding birds gather in groups of 40 or 50 during the breeding season. The smaller dark-plumaged Abdim's stork is often encountered with white stork flocks in southern Africa. Breeding pairs of white stork may gather in small groups to hunt, and colony nesting has been recorded in some areas. However, groups among white stork colonies vary widely in size and the social structure is loosely defined; young breeding storks are often restricted to peripheral nests, while older storks attain higher breeding success while occupying the better quality nests toward the centres of breeding colonies. Social structure and group cohesion is maintained by altruistic behaviours such as allopreening. White storks exhibit this behaviour exclusively at the nest site. Standing birds preen the heads of sitting birds, sometimes these are parents grooming juveniles, and sometimes juveniles preen each other. Unlike most storks, it never adopts a spread-winged posture, though it is known to droop its wings (holding them away from its body with the primary feathers pointing downwards) when its plumage is wet.
A white stork's droppings, containing faeces and uric acid, are sometimes directed onto its own legs, making them appear white. The resulting evaporation provides cooling and is termed urohidrosis. Birds that have been ringed can sometimes be affected by the accumulation of droppings around the ring leading to constriction and leg trauma.The white stork has also been noted for tool use by squeezing moss in the beak to drip water into the mouths of its chicks.
Voice, singing & call
The adult white stork's main sound is noisy bill-clattering, which has been likened to distant machine gun fire. The bird makes these sounds by rapidly opening and closing its beak so that a knocking sound is made each time its beak closes. The clattering is amplified by its throat pouch, which acts as a resonator. Used in a variety of social interactions, bill-clattering generally grows louder the longer it lasts, and takes on distinctive rhythms depending on the situation—for example, slower during copulation and briefer when given as an alarm call. The only vocal sound adult birds generate is a weak barely audible hiss; however, young birds can generate a harsh hiss, various cheeping sounds, and a cat-like mew they use to beg for food. Like the adults, young also clatter their beaks. The up-down display is used for a number of interactions with other members of the species. Here a stork quickly throws its head backwards so that its crown rests on its back before slowly bringing its head and neck forwards again, and this is repeated several times. The display is used as a greeting between birds, post coitus, and also as a threat display. Breeding pairs are territorial over the summer, and use this display, as well as crouching forward with the tails cocked and wings extended. Distribution, habitat & migration
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.
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 (Bikaner) and southern (Tirunelveli) 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. 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 there as farmland was succeeded by tall grass 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.
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 thought to have established in the 16th century after forests were cut down for agriculture. About 5000 pairs were estimated to breed in the 18th century which declined subsequently. The first accurate census in 1917 found 25 pairs and the last pair failed to breed around 1955. 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 an re-introduction initiative 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 (3000 ft) 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 (Greater Poland Voivodeship) 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.
Systematic research into migration of the white stork began with German ornithologist Johannes Thienemann who commenced bird ringing studies in 1906 at the Rossitten Bird Observatory, on the Curonian Spit in what was then East Prussia. Although not many storks passed through Rossitten itself, the observatory coordinated the large-scale ringing of the species throughout Germany and elsewhere in Europe. Between 1906 and the Second World War about 100,000, mainly juvenile, white storks were ringed, with over 2,000 long-distance recoveries of birds wearing Rossitten rings reported between 1908 and 1954.
White storks rely on the uplift of air thermals to soar and glide the long distances of their annual migrations between Europe and Sub-Saharan Africa. For many, the shortest route would take them over the Mediterranean Sea; however, since air thermals do not form over water, they generally detour over land to avoid the trans-Mediterranean flights that would require prolonged energetic wing flapping.[64] It has been estimated that flapping flight metabolises 23 times more body fat than soaring flight per distance travelled.[65] Thus, flocks spiral upwards on rising warm air until they emerge at the top, up to 1,200–1,500 m (3,900–4,900 ft) above the ground (though one record from Western Sudan observed an altitude of 3,300 m (10,800 ft)).[56]
Long flights over water may occasionally be undertaken. A young white stork ringed at the nest in Denmark subsequently appeared in England, where it spent some days before moving on. It was later seen flying over St Mary's, Isles of Scilly, and arrived in a poor condition in Madeira three days later. That island is 500 km (320 mi) from Africa, and twice as far from the European mainland. Migration through the Middle East may be hampered by the khamsin, winds bringing gusty overcast days unsuitable for flying. In these situations, flocks of white storks sit out the adverse weather on the ground, standing and facing into the wind. Hunting & food
White storks consume a wide variety of animal prey. They prefer to forage in meadows that are within roughly 5 km (3 mi) of their nest and sites where the vegetation is shorter so that their prey is more accessible. Their diet varies according to season, locality and prey availability. Common food items include insects (primarily beetles, grasshoppers, locusts and crickets), earthworms, reptiles, amphibians, particularly frog species such as the edible frog (Pelophylax kl. esculentus) and common frog (Rana temporaria) and small mammals such as voles, moles and shrews. Less commonly, they also eat bird eggs and young birds, fish, molluscs, crustaceans and scorpions. They hunt mainly during the day, swallowing small prey whole, but killing and breaking apart larger prey before swallowing. Rubber bands are mistaken for earthworms and consumed, occasionally resulting in fatal blockage of the digestive tract.
Birds returning to Latvia during spring have been shown to locate their prey, moor frogs (Rana arvalis), by homing in on the mating calls produced by aggregations of male frogs.
The diet of non-breeding birds is similar to that of breeding birds, but food items are more often taken from dry areas. White storks wintering in western India have been observed to follow blackbuck to capture insects disturbed by them. Wintering white storks in India sometimes forage along with the woolly-necked stork (Ciconia episcopus). Food piracy has been recorded in India with a rodent captured by a western marsh harrier appropriated by a white stork, while Montagu's harrier is known to harass white storks foraging for voles in some parts of Poland. White storks can exploit landfill sites for food during the breeding season, migration period and winter. Breeding & mating
The white stork breeds in open farmland areas with access to marshy wetlands, building a large stick nest in trees, on buildings, or on purpose-built man-made platforms. Each nest is 1–2 m (3.3–6.6 ft) in depth, 0.8–1.5 m (2.6–4.9 ft) in diameter, and 60–250 kg (130–550 lb) in weight. Nests are built in loose colonies. Not persecuted as it is viewed as a good omen, it often nests close to human habitation; in southern Europe, nests can be seen on churches and other buildings. The nest is typically used year after year especially by older males. The males arrive earlier in the season and choose the nests. Larger nests are associated with greater numbers of young successfully fledged, and appear to be sought after. Nest change is often related to a change in the pairing and failure to raise young the previous year, and younger birds are more likely to change nesting sites.[80] Although a pair may be found to occupy a nest, partners may change several times during the early stages and breeding activities begin only after a stable pairing is achieved.
Several bird species often nest within the large nests of the white stork. Regular occupants are house sparrows, tree sparrows, and common starlings; less common residents include Eurasian kestrels, little owls, European rollers, white wagtails, black redstarts, Eurasian jackdaws, and Spanish sparrows. Paired birds greet by engaging in up-down and head-shaking crouch displays, and clattering the beak while throwing back the head. Pairs copulate frequently throughout the month before eggs are laid. High-frequency pair copulation is usually associated with sperm competition and high frequency of extra-pair copulation; however, extra-pair copulation is infrequent in white storks. Chicks, juveniles & raise
A white stork pair raises a single brood a year. The female typically lays four eggs, though clutches of one to seven have been recorded. The eggs are white, but often look dirty or yellowish due to a glutinous covering. They typically measure 73 mm × 52 mm (2.9 in × 2.0 in), and weigh 96–129 g (3.4–4.6 oz), of which about 11 g (0.39 oz) is shell. Incubation begins as soon as the first egg is laid, so the brood hatches asynchronously, beginning 33 to 34 days later. The first hatchling typically has a competitive edge over the others. While stronger chicks are not aggressive towards weaker siblings, as is the case in some species, weak or small chicks are sometimes killed by their parents.This behaviour occurs in times of food shortage to reduce brood size and hence increase the chance of survival of the remaining nestlings. White stork nestlings do not attack each other, and their parents' method of feeding them (disgorging large amounts of food at once) means that stronger siblings cannot outcompete weaker ones for food directly, hence parental infanticide is an efficient way of reducing brood size. Despite this, this behaviour has not commonly been observed.
The temperature and weather around the time of hatching in spring is important; cool temperatures and wet weather increase chick mortality and reduce breeding success rates. Somewhat unexpectedly, studies have found that later-hatching chicks which successfully reach adulthood produce more chicks than do their earlier-hatching nestmates. The body weight of the chicks increases rapidly in the first few weeks and reaches a plateau of about 3.4 kg (7.5 lb) in 45 days. The length of the beak increases linearly for about 50 days. Young birds are fed with earthworms and insects, which are regurgitated by the parents onto the floor of the nest. Older chicks reach into the mouths of parents to obtain food. Chicks fledge 58 to 64 days after hatching.
White storks generally begin breeding when about four years old, although the age of first breeding has been recorded as early as two years and as late as seven years. The oldest known wild white stork lived for 39 years after being ringed in Switzerland, while captive birds have lived for more than 35 years.