Photo : pellets of White Storks (Natuurpunt vzw)
Storks are not very restricted in their menu. They hunt, stepping slowly through low vegetation, on earthworms, large insects –locusts and beetles- , frogs, snails, lizards, snakes, mice and moles. Fish is not often on their menu and when, they eat mostly dead fish.
Storks often look for food on garbage dumps and slaughter places.
They hunt on sight and when it localised a prey, the stork can run fast and will try to spear the prey.
The largest prey they can swallow easily is a mole or fish of up to 20 cm. Swallowing these or larger preys is not without danger. The claws of the mole and the spines of the fish can damage the gullet of the stork. Hairs, feathers, wing-sheaths of beetles and other tuff material leaves the stork in the form of a pellet.
During the migration and winter period the storks can flock in groups of 50.000 to 100.000 individuals on places where locust outbreaks occur.
Storks gather at the edge of savannah fires to catch the confused and wounded insects and little animals.
The reason why some of the Belgian storks sometimes prefer the Sahel instead of the inner delta of the river Niger can be explained in the amount of yearly rainfall. When it rains, the desert blooms and the vegetation responds quickly to this new situation. The insects, especially locusts, explore this habitat also very fast and will start short breeding cycles. These locusts and other large insects are an important food item of storks. Lucky for the storks their haven’t been severely dry periods in the region. After the summer rains the Sahel attracts the locusts and these attract predators as eagles, falcons and storks. Although these predators can occur in large numbers they do not have a significant impact on the total population of pest species as locusts, which easily occur in groups of millions of individuals. The Stork can eat every day hundred of locusts, which only have a weight of tenths of a gram to 1 or 2g.
The Food and Agriculture organisation of the United Nations (FAO) is monitoring closely the development and movements of the locust species. Not to track storks, but to be able to start eradication campaigns whenever the FAO believes it is necessary.
One of the items you can find on this site is the monthly rainfall report. This is shown on figure 1 where you see the large amount of rainfall in August 2000 in the southern part of Mauritania.
Figure 1 : red squares indicate places where more than 50 mm rain was measured + = weather stationAls ze een prooi hebben opgemerkt, kunnen ze die bliksemsnel en trefzeker met hun sterke, lange en puntige snavel vastgrijpen.
source : FAO
After the rainfall and together with the growth of the vegetation the grasshoppers arrive in the area and start laying eggs. On figure 2 the blue spots indicate concentrations of grasshoppers in the south of the Sahara, especially Mauritania, where the tagged storks were staying.. Bon appetit!
The pattern we have seen in 2000 repeats itself as you can see on figure 3 where you can see the large concentrations of locusts in southern Mauritania.
Because of the opportunistic behaviour of the stork, it has to follow the locust groups when they have to leave drying areas. This often erratic behaviour of the White Stork in the winter quarters makes it difficult to take effective protective measures. The birds often move from one agricultural area to the other. Nevertheless we can improve the conditions along the migration route, by restructuring overhead powerlines, creating safe stopover sites and by putting an end to poaching.