Migrant Birds – White Stork
While generally very abundant world-wide, this bird’s numbers vary in South Africa depending on conditions elsewhere in the subregion. This is a Paleoarctic breeding migrant, which usually arrives in our country from October and departing between March and May. Most birds come from central and eastern Europe and the Middle East, sometimes travelling a round trip of some 22 000 kilometres! Overwintering birds (which tend to be injured birds or juveniles) may be found in the Drakensberg escarpment and in Zimbabwe. It is thought that some fledglings migrating from the Western Cape may overwinter in central Africa. The South African breeding population is small and rarely numbers more than 10 pairs. Mortality rates are high and are usually caused by injuries of some sort – collisions with vehicles, fences or wires/lines, weather conditions, predation, shooting and trapping, electrocution, poisoning, starvation and drowning. However, the birds are not globally threatened, despite breeding range reduction in Europe. They were previously classified as “rare” in southern Africa but are no longer of regional conservation concern. Food contaminated by pesticides has long been considered a significant threat but there is no proof of extensive mortalities during locust control operations.
White Storks are found in open woodland, grasslands, grassy Karoo, wetlands and cultivated lands, especially lucerne fields; some 86% of birds in South Africa are found in crop fields and pastures – which is where we have also seen large flocks. They are mostly absent from large permanent wetlands and flood plains.
The birds are usually seen in large flocks of 10 – 50 birds and may gather in groups around water sources at midday. They sometimes rest on one leg with the bill buried in the ruff of the foreneck, a behaviour thought to minimise heat loss. In hot weather, they also cool down by defecating on the legs. They roost gregariously in trees or shallow wetlands, sometimes with Abdim’s Storks. They travel in large flocks, circulating on thermals to gain height and then gliding to another thermal; this becomes more frequent before their northern migration begins. They fly with neck and legs fully extended. White Storks undergo a complete annual moult but no data is available for South African birds.
They normally forage in well-spaced groups, sometimes in association with Abdim’s Storks. They walk slowly and steadily as they search for prey. They follow ungulates and domestic cattle, apparently to capture flushed insects. They take up to 45 items per hour. In the grassy Karoo, locusts are picked up at an average of 5.8 per minute! They eat agricultural pests such as the American bollworm, army worms and locusts. When feeding on the latter, they deposit significant fat reserves. They also eat mice, small reptiles (snakes and lizards), amphibians, fish, molluscs and large insects, young of ground-breeding birds, scorpions and the caterpillars of the Emporer Moth, as well as termite alates.
Their breeding habits are little known in southern Africa, as so few breed here. They are known to be monogamous. The male arrives at the nest site first and may accept the first female to arrive, often the mate of the previous year. They display frequently. The nest is built by both sexes in about eight days, with most of the material being brought in by the male. It consists of a large platform of reeds, sticks, clods of earth and grass with an outside diameter of 80 – 150 cm and being between 1 – 2 m high. Nest material is added constantly, even after the young are fledged, with material gathered from up to 500 m away. The nest is usually placed in a tree in open veld, most in alien trees. 1 – 6 eggs are laid at 1 – 4 day intervals in September, October and November. Incubation lasts 30 days and is shared by both sexes. Eggs hatch asynchroniously and young are brooded by both male and female. The bird is fully feathered at 45 days but flaps its wings as early as 14 days and is able to stand at 22 days. The nestling period lasts up to between 45 – 70 days, when the birds are fed by both adults. The young are dependent on the adults for 7 – 20 days after leaving the nest and then disperse. The adults remain at the nest for a further period of 15 – 30 days before departing. Breeding success – approx 50%.
See this bird on grasslands and pastures during the South African summer, when they may often be seen with herds of cattle or sheep or simply foraging or roosting in flocks.
