White Stork

White storks are expert soarers. Flocks ride rising thermals, climbing to about 1,200 to 1,500 m (3,900 to 4,900 ft), then glide onward with few wingbeats, saving energy on journeys of more than 6,000 km (3,700 mi) between Eurasia and Africa. Because thermals do not form over water, storks avoid crossing the open Mediterranean. Western birds funnel through the Strait of Gibraltar, and eastern birds cross the Bosphorus in Turkey. Tracked juveniles on the eastern route flew for about 13 to 15 days, averaging roughly 273 km (170 mi) a day. Tailwinds, and scarce food or water along the way, raise average speed. Autumn journeys average about 26 days overall and spring journeys about 49, and BirdLife records a top gliding speed of 110 km/h (68 mph). Migration happens by day.

Life is hardest for young white storks. Ringing data suggest only about 33 percent of juveniles survive a year, compared with about 83 percent of adults. In one tracking study of 32 young storks migrating from Germany to Africa, 25 completed the journey and survived past October, about 78 percent. Four died on migration and three in the first month of wintering, with causes including fatigue, illness, and hunting. The clearest warning sign was energy: birds that later died burned significantly more energy flying early in migration, while weather, departure timing, and pre-migration flight experience did not differ. Electrocution is also a very common cause of stork deaths. Survivors can live long: the oldest ringed bird reached 39 years, and ADW gives a typical wild lifespan of 20 to 25 years.

White storks are opportunistic hunters. They feed mainly by day in meadows and shallow water, usually within about 5 km (3 mi) of the nest, and favor shorter vegetation where prey is easier to find. Their varied menu includes beetles, grasshoppers, crickets, earthworms, frogs, reptiles, and small mammals such as voles, moles, and shrews, and less often fish, young birds, and eggs. BirdLife adds carrion. Small prey is swallowed whole, while larger prey is broken up first. The diet shifts with conditions: in dry years storks eat mostly insects and mice, while in wet years they take mostly aquatic animals, according to Animal Diversity Web. This flexibility helps them cope when one kind of prey becomes scarce and lets them use very different habitats across Europe, Asia, and Africa.

Adult white storks have no real voice, only a weak, barely audible hiss, so bill-clattering is their main sound. The rapid snapping is likened to distant machine-gun fire, and the throat pouch amplifies it. Storks clatter in many social situations: territorial pairs combine clattering with an up-down head display in summer, the clatter slows during mating, and it becomes briefer as an alarm. Chicks, by contrast, beg with a cat-like mew. Animal Diversity Web also reports soft cooing during courtship and loud warnings to intruders, so sources differ on whether adults ever vocalize. Males arrive a few days before females each spring to claim a nest, and pairs then use displays at the nest to reinforce their bond. For a nearly voiceless bird, clattering carries a great deal of meaning.

White storks build large stick nests in trees, on rooftops and chimneys, and on platforms, including poles fitted with platforms in Poland to keep nests away from wires. A typical nest is 1 to 2 m (3.3 to 6.6 ft) deep, 0.8 to 1.5 m (2.6 to 4.9 ft) across, and weighs 60 to 250 kg (130 to 550 lb), though 145 weighed Polish nests averaged almost 400 kg (880 lb), and one reached 964 kg (2,125 lb). Pairs return each year to repair and add to the nest, and males, which arrive first, often reclaim the previous year’s nest, so one can last for several years. Decomposition limits their growth. Larger nests are linked to more fledged young, but building on structures near people exposes storks to electrocution and collisions.

Both parents share incubation, which lasts 33 to 34 days, and both feed the young. The typical clutch is four eggs, though one to seven have been recorded, and there is one brood a year. Touch is part of communication between parents and young, according to Animal Diversity Web. They fledge 58 to 64 days after hatching, and parents keep feeding them for another 7 to 20 days. Success depends on conditions: cool, wet weather around hatching lowers breeding success, and larger nests are associated with more young fledged. Breeding usually begins at about four years old, though the recorded range is two to seven. After a long decline from the 19th century, white storks have recovered in many places, and the global population is estimated at about 700,000 birds.