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A carnivore with a big appetite
The White Stork, perched on the long stilt-like legs of a wading bird, is at home with its feet in the water (marshes, shallow lakes, flooded meadows…). It lives in temperate and Mediterranean Europe, in North and South Africa and Eastern Asia. It spends the winter in Africa, India and Southern Asia.
The White Stork is a carnivore. It needs 250 to 400 g of animal proteins each day. First and foremost, it attacks insects and gastropods, but also larger prey, such as frogs and toads, small rodents and fledglings. Like a bird of prey, the stork eats its victims whole, bones, fur, feathers and all, then regurgitates those elements that are not digested in the form of dry pellets : regurgitation pellets.
A ace at gliding and soaring
When food is lacking in its area, the White Stork takes off for milder regions. It adopts the gliding technique favoured by birds with a large wingspan, consisting of taking advantage of “thermals” or “updrafts”, pockets of warm air with a tendency to rise in altitude.
The White Stork, with its 2-metre wingspan, is a fully-fledged member of the gliding aces club. It spots the formation of thermals, by identifying the upward movement of insects or pieces of straw, for example, and uses the updrafts like we would take a lift.
The migratory journey of the stork therefore resembles a succession of « roller coaster rides» : it finds a thermal that takes it to an altitude of several hundred metres, then glides towards the Earth until it finds another thermal.
Migratory or sedentary ?
Gliding with wings outstretched is a far less exhausting technique than flying by flapping the wings: It requires about a twentieth of the energy. Nevertheless, migration represents a major expenditure of energy. Sometimes, certain White Storks even choose to confront cold and starvation in their region rather than migrate.
This is the case, in Alsace, for example, where more and more sedentary storks are sighted. The more clement winters and feeding by local authorities or private individuals, who do not want to see this bird disappear from their region, do not encourage the storks to migrate.
Scientists are studying these new behaviour patterns closely. In particular, they want to know if this sedentary lifestyle will have repercussions on reproduction. Generally, migrating specimens, theoretically in better physical shape, rear a larger number of chicks than sedentary storks already occupying a territory. |