The White Stork is a large bird. It has a length from the tip of its beak to the tip of its tail of 100–115 cm (39–45), a wingspan of 195–215 cm (77–85), and a weight of 2.3–4.4 kg (5.1–9.7 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 coloration 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.
Beaks turn red starting at the base. 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 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 White Stork is a rare visitor to the British Isles, though in 1416 a pair nested atop St Giles's Church in Edinburgh, Scotland. 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 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 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.
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.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 urine, 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 their chicks.
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. 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.
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.
Breeding and lifespanEdit
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. A succession of pairs have been observed occupying a nest for a few days before moving on, the reason for which is unclear.
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, Black Redstarts and Eurasian Jackdaws. 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.
A White Stork pair raises a single brood a year. The female typically lays four eggs, though clutches of 1–7 have been recorded. The eggs are white, but often look dirty or yellowish due to a glutinous covering. They measure 72.58 ×51.86 mm (2.857 ×2.042 in), and weigh 96–129 g (3.4–4.6 oz), of which 10.76 g (0.380 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.