Ardea
Official journal of the Netherlands Ornithologists' Union

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Rooth J. (1957) Over het voedsel, de terreinkeus en de achteruitgang van de Ooievaar, Ciconia ciconia L., in Nederland. ARDEA 45 (3-4): 93-116
On the food, habitat selection and decline of the population of the White stork, Ciconia c. ciconia L., in the Netherlands.1. This paper is intended as a contribution to the white stork investigation in the Netherlands in as much as the decline of its population is influenced by the food. 2. In literature a decrease of the number of white storks in Western Europe is mentioned from 1940 onwards. During the last years, however, an increase in Spain (Bernis 1954) and Eastern Europe (Hornberger 1952) has been stated. In Eastern Europe relatively high population densities have been found of 60 and more breeding pairs in 100 km2. This is the case in the centre of the breeding area of the Northern European population, which is situated between the Baltic and the Black Sea, especially in Poland. For the present the population density in the Netherlands, being the utmost Western part of the area, is 0.1-0.2 breeding pairs in 100 km2. 3. In this country observations were made at two nests: one in the neighbourhood of Groningen and the other near Utrecht. The areas where the storks on the nests collected their food were respectively about 35 km2 and 25 km2. In Groningen the situation was favourable for studying whether the storks preferred grasslands with either a high or a low ground water level. In 1954 no preference was noticed which might be caused by the abnormal wetness of the summer of 1954. 4. Unlike the heron, the white stork normally walks when collecting food. Frogs, mice and smaller preys are swallowed after catching. Moles need a special operation. In the Netherlands the storks often collect their food walking behind a mowing machine. In Germany (Schuz 1940 a) in spring also behind the plough. 5. The following methods of food analysis are discussed: a. Observations of food collecting storks. The difficulty is that only the bigger prey can be determined. b. Observations at the nest when feeding the young. It is very difficult and mostly impossible to distinguish what prey are offered to the young. c. Stomach analysis. This method is perfect but not practicable in this country because of the small population. d. Analysis of the pellets. The results of stomach analysis recorded in literature are given (272 stomachs). They contained: Hares 1 Frogs 114 Spiders 9Moles 33 Toads 4 Flies and mosquitoes 21Rats 1.5 Salamanders 1 Dragonflies 5Voles and mice 198 Fishes 6 Mollusc 57Birds 8 Beetles 710 Earth worms 600Eggs 3 Locusts 6,000-7,000 Blood suckers 10Lizards 38 Crickets 341 Remains of plants 165Snakes 14.5 Caterpillars 23The results of pellets' analysis recorded in literature are given. They contained:Moles 7 Fishes some remainsVoles and mice 5 Insects and spiders 1,248Birds 2 Blood suckers 3Frogs some remainsHaverschmidt (1949) gives another record of 10 pellets: 34 Carabidae, 50 Hydrophilidae, 6 Dytiscidae, 1 Coccinellidae. Different observations are discussed about the number of prey caught during one single collecting expedition of a bird from the nest near Groningen. One hundred small preys and one frog were caught on one occasion in an hour, on another occasion 50 small prey were taken in 5 minutes. 6. Observations of food preference as given in the literature are discussed. 7. As far as could be traced there seems to be a special preference for habitats showing rather considerable differences of soil-types, altitude and ground water level at a relatively small distance. This applies to different parts of the breeding area (Spain, Netherlands, and Schleswig-Holstein). 8. The preference for such habitats seems to be favourable for the availability of sufficient quantities of food as well in wet as in dry seasons. In the Netherlands a positive correlation may be noticed between the distribution of the white stork and the vole (Microtis arvalis). Concentrations of stork nests are+ found in those areas where vole plagues occur. A high vole population is mostly found where grassland cultivation is extensive (van Wijngaarden 1957). 9. The decline of the white stork population is this country is discussed. 66% of the young white storks start breeding at a short distance (25 km) from their native nest. Therefore a local decrease in number cannot normally be supplemented by birds from other places. 10. The different factors causing the decline of the population are: shooting (mostly on migration), lack of food, nest fights, parasitism, struggle in migration flocks, mechanical death, and diminution of the favourable habitat (in the Netherlands diminution of extensively cultivated grasslands). From the latter an example is shown on a map of the province of Drenthe (the Netherlands). Conclusion None of the various factors discussed playa particularly important part, perhaps with the exception of the shooting. However, they all work towards the same end, forming together the cause of decline in question, which probably cannot be stopped. In fact it only represents a relatively insignificant shrinking of the distribution, as the populations in Spain and Eastern Europe seem to remain at the same level while in some places there is even an increase.


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