White stork

Name and taxonomy

Francis Willughby wrote about the bird in the 17th century and called it Ciconia alba. His account rested on a drawing that Sir Thomas Browne of Norwich had posted to him. Carl Linnaeus listed it in 1758 as Ardea ciconia. Mathurin Jacques Brisson moved it into a new genus, Ciconia, in 1760. Both halves of the modern name come from the Latin word for stork.

Two subspecies are recognised. The nominate form breeds in Europe, northwest Africa, western Asia and southern Africa. Nikolai Severtzov described the eastern form in 1873. It breeds in Turkestan, winters between Iran and India, and is a little larger. Wikidata also records the name European white stork.

Evolution and relatives

The stork family holds 20 living species in six genera. They fall into three groups: the open-billed and wood storks, the giant storks, and the typical storks. The white stork belongs to the typical storks, which have straight pointed bills and black and white plumage. Its nearest relatives are the oriental stork of east Asia and the maguari stork of South America. The oriental bird was once treated as a subspecies of this one.

Behaviour and genetics both point to the same close grouping inside Ciconia. Studies used mitochondrial cytochrome b sequences and DNA hybridisation. A fossil arm bone from Rusinga Island in Kenya is 24 to 6 million years old. It may belong to the white stork or to the black stork, because the two share a bone plan. More remains have come from the Middle Miocene beds of Maboko Island.

Appearance

The plumage is white apart from the black flight feathers and wing coverts. Melanin gives those feathers their colour. The breast feathers are long and shaggy, and form a ruff used in display. The eye is dull brown or grey, and the skin around it is black. Carotenoids from the diet give the bill and the legs their red. In parts of Spain that pigment comes from an introduced crayfish.

An adult measures 100 to 115 cm long and spans 155 to 215 cm. A bird weighs 2.3 to 4.5 kg, and males average larger than females. The sexes are alike in plumage. A chick hatches under thin whitish down, which a woolly coat replaces within a week. Black shoulder and flight feathers appear by three weeks. A young bird takes adult colours by its second summer.

Habitat and range

The white stork feeds in grassy meadows, farmland and shallow wetland. It avoids ground under tall grass and scrub, where prey is hard to see. It nests in open farmland close to marshy ground. Its needs match those of farmers, which has tied the bird to people for centuries. A quarter of the world population breeds in Poland.

The eastern subspecies numbers about 1450 birds between the Aral Sea and Xinjiang. The Chinese part of that group is thought to have died out around 1980. Winter takes the species to Tunisia, Uganda, Angola, Zambia, Botswana and many other African countries. A small number winter in India instead. Estonia holds about 5000 breeding pairs, while nearby Finland has almost none. The range has spread east into western Russia in recent years.

Storks near Chernobyl fell away after the accident of 1986, as farmland turned to scrub. In parts of Poland, thin feeding grounds have pushed birds onto rubbish dumps since 1999. Storks also forage on dumps in the Middle East, North Africa and South Africa. Litter turned up in the pellets of a third of Polish breeding pairs. In southern Poland the birds first bred in the Podhale uplands in 1931. They have nested higher ever since, and reached 890 metres in 1999.

Diet and feeding

The white stork is a carnivore with a very wide menu. Beetles, grasshoppers, locusts and crickets make up much of the insect share. Earthworms, frogs, lizards, snakes and small mammals such as voles and moles are all taken. Fish, molluscs, crustaceans, scorpions, bird eggs and nestlings appear less often. The bird hunts by day and walks slowly with the bill angled down. It jabs forward when it sees prey, then swallows small items whole.

Pairs prefer meadows within about 5 km of the nest. In dry years the diet leans on insects and mice, and in wet years on water animals. Locust and armyworm outbreaks draw storks in large numbers. Birds back in Latvia in spring find moor frogs by listening for the male chorus. Storks in India follow blackbuck and catch the insects the antelope disturb. Rubber bands are sometimes swallowed as worms, and they can block the gut.

Behaviour and social life

The white stork is sociable and gathers in flocks of thousands on migration. Non-breeding birds form groups of 40 or 50 during the breeding season. Nesting is loosely colonial, and the structure of a colony is not fixed. Older birds hold the central nests and raise more young. Young breeders are pushed to the edge of the group.

Birds preen each other at the nest, and nowhere else. A standing bird grooms the head of a sitting bird. Parents preen chicks, and chicks preen each other. A stork walks slowly with the neck up, and rests with the head between the shoulders. It never spreads its wings in the sun, though it lets them droop when wet.

A stork sometimes aims its droppings onto its own legs, which turns them white. The water evaporates and cools the bird, a trick called urohidrosis. The species also uses a tool: a parent squeezes wet moss to drip water into a chick. Flapping flight burns 23 times the fat of soaring over the same distance. So a stork climbs on a thermal to 1200 or 1500 metres and glides on.

Communication and senses

An adult white stork has almost no voice. Storks do own a syrinx, but it is poorly developed and little used. The main sound is bill-clattering, made by snapping the beak open and shut. The throat pouch works as a resonator and carries the noise a long way. Clattering grows louder the longer it runs, and its rhythm changes with the situation.

The only voiced sound from an adult is a faint hiss. A chick can hiss harshly, cheep, and mew like a cat when it begs. Chicks over 14 days old tap the parent's bill to ask for food. In the up-down display, a bird throws its head back onto its own crown and returns it slowly. The same display serves as a greeting, as a follow-up to mating, and as a threat.

Reproduction and life cycle

Males return to the breeding grounds first, in March or April. A male picks a nest and builds it up before the female arrives. The nest is a mass of sticks in a tree, on a roof or on a purpose-built platform. It stands 1 to 2 metres deep and 0.8 to 1.5 metres across. A long-used nest can weigh 60 to 250 kilograms. Larger nests raise more young, so birds compete for them.

A pair greets with head-shaking and up-down displays and loud clattering. Pairs mate often through the month before laying. The bond is strong, and a pair usually keeps the same nest from year to year. A female lays four eggs in a normal year, and clutches of one to seven are known. An egg measures about 73 by 52 millimetres and weighs 96 to 129 grams. About 11 g of that weight is shell.

Incubation starts with the first egg, so the chicks hatch on different days. Hatching comes 33 to 34 days after laying, and both parents take turns. A chick reaches about 3.4 kg by 45 days. The young leave the nest 58 to 64 days after hatching. The parents feed them for a further 7 to 20 days. Birds first breed at 3 to 5 years, and wild storks live 20 to 25 years.

Predators and threats

An adult white stork has few predators. Hawks and eagles take nestlings and fledglings. A nest set high on a roof or a tree keeps ground animals away. Parents defend the young hard. Mortality after the second year runs at about 21 percent, and it is higher before that.

Parasites matter more than predators for this bird. Chewing lice and feather mites live in the plumage and feed on fungi there. A survey of twelve nests found 13352 mites of 34 species. Those nest mites eat insect eggs and nematodes, and parasitic mites were absent. Flukes, tapeworms and roundworms all live inside the bird.

Drained wetlands and ploughed meadows remain the largest threat. Storks also collide with overhead power lines. Pesticides used against African locusts reach the birds that eat them. Illegal shooting continues along the migration routes. A ring on the leg can gather droppings, which may tighten and injure the leg.

Population and conservation

The IUCN has rated the white stork as Least Concern since 1994. It stood at Near Threatened in 1988. The last wild birds went from Belgium in 1895, Switzerland in 1950 and Sweden in 1955. The Netherlands lost its last wild pair in 1991. Reintroduction has since brought the bird back to all four countries.

A census in 2004 and 2005 counted 52500 pairs in Poland. Spain held 33217 pairs and Ukraine 30000. Lithuania holds the densest population in the world, at 13000 pairs. Western Europe counted far fewer, with 973 French pairs and 528 Dutch ones. iNaturalist holds 84322 observations, and GBIF records the bird from 140 countries.

The species is covered by the agreement on African-Eurasian migratory waterbirds. Numbers have risen by about 20 percent under new land-use rules. Spain and the countries of eastern Europe led that recovery. In England, storks bred at Knepp in 2020 for the first time in 600 years. Young birds were held in a 2.6 hectare pen there until they were old enough to release.

Relationship with humans

The white stork probably lives closer to people than any other large wild bird in Europe. It nests on churches, chimneys, hay stacks, ruins and electricity pylons. German, Dutch and Polish households built platforms to invite a pair in. The bird gained from medieval clearance of woodland. It lost heavily to drainage and industrial farming in the 19th century.

Farmers value the stork because it eats grasshoppers and other pests. A nest on a chimney or a pylon can be a hazard, and Polish groups move such nests. Ringing began at Rossitten in 1906 under Johannes Thienemann. About 100000 storks were ringed in Europe before the Second World War. That work produced over 2000 long-distance recoveries between 1908 and 1954.

In culture and myth

In European folklore, the stork delivers babies to new parents. Hans Christian Andersen made the old story famous in the 19th century. German tellings had the bird lift babies from caves or marshes. A household that wanted a child left sweets on the window sill. A birthmark on the back of a baby's head is still called a stork bite.

In Slavic belief, storks carried unborn souls from Vyraj to the world in spring. Early Slavs held that killing a stork brought bad luck. Greek and Roman writers made the stork a model parent. The Greek law called Pelargonia required a citizen to look after aged parents. Hera turned the Trojan princess Antigone into a stork for claiming equal beauty. The bird appears in at least three of Aesop's fables.

Muslims respected storks because the yearly journey looked like a pilgrimage to Mecca. In German belief, a nest on a house guarded it against fire. A stork shot in Germany in 1822 carried a 75 cm African spear through the neck. That bird ended older ideas that birds slept the winter under water. It stands today in the collection of the University of Rostock.