424 The Food Composition of Immature and Non-breeding White Storks in Poland MARCIN ANTCZAK 1 , SZYMON KONWERSKI 2 , SEWERYN GROBELNY 3 AND PIOTR TRYJANOWSKI 3,4 1 Department of Zoology, Faculty of Biological Sciences, University of South Bohemia Branisovská ˇ 31, ˇ Ceské Budejovice, ˇ CZ-370 05, Czech Republic 2 Department of Systematic Zoology, Adam Mickiewicz University, Fredry 10, PL-61-701 Pozna´ n, Poland 3 Department of Avian Biology and Ecology, Adam Mickiewicz University, Fredry 10, PL-61-701 Pozna´ n, Poland 4 Corresponding author: e-mail: ptasiek@main.amu.edu.pl Abstract.—The food of immature White Storks (Ciconia ciconia) feeding in meadows in Poland was studied by pellet analysis. The most important food items by numbers were insects, mainly beetles, which constituted 83% of all prey items (N = 5,958 items) and were found in all pellets (N = 163). However, by biomass, 58% of food consisted of small mammals, mainly voles Microtus sp. Insects (22%) and earthworms (11.5%) were secondary resources. Lit- erature on White Stork diet in Europe also showed that voles, insects and earthworms were the dominant food of breeding White Storks. Their roles changed with latitude, habitat, time, as well as method of data analysis. Gener- ally, the diet of non-breeding storks was similar to breeding birds, but more of the prey was obtained in dry habitats. Received 6 March 2002, accepted 10 July 2002. Key words.—Ciconia ciconia, diet, non-breeders, pellet analysis, White Stork. Waterbirds 25(4): 424-428, 2002 The food resources, both in breeding and wintering areas, were shown to be a key factor affecting the number of White Stork (Ciconia ciconia) (Dallinga and Schoenmakers 1987; Goriup and Schulz 1991). White Stork diets have been described in detail from many lo- calities in the Palearctic region (see review in Creutz 1985; Schulz 1998). However, the diet analyses were restricted to breeding birds (Creutz 1985; Schulz 1998). Knowledge of the diet of non-breeding birds could be useful for the management of the White Stork, but have not been studied (Goriup and Schulz 1991). Generally, first breeding in the White Stork starts when the birds are three years old or older (Creutz 1985; Schulz 1998). Many im- mature birds remain in South Africa during their first three years, but some, especially three and/or four-year-olds, migrate to Eu- rope. Here they occur in small flocks and spend the time in meadows and pastures. In this paper, the diet of non-breeding, young White Storks that spent the summer in Poland is examined, and a comparison with the diet of breeding birds is reported. Comparability of results from different stud- ies using different methods of food analysis is discussed. MATERIAL AND METHODS Study Area The study area was in the eastern part of the Barycz River valley (western Poland). This is a typical lowland river valley, with mixed agriculture, and containing a high proportion of meadows and arable fields. Parts of lower meadows are regularly flooded during early spring (March-April). The number of breeding White Storks in this area is stable, with one of the highness den- sities in western Poland (ca. 52 breeding pairs/100 km 2 ; P. T. Dolata, unpubl. data). Within this area, non-breed- ing storks regularly fed and roosted together during late spring and summer. During May and June 2000, seven to 30 storks roosted on dead oak (Quercus sp.) and during the day, they foraged in small flocks of four to eleven in- dividuals. Diet Analysis A total of 163 pellets were collected from the roost site during May and June 2000. Pellets were soaked in water and washed through a sieve (1 mm mesh). All food remains were compared with a reference collec- tion taken from the Wielkopolska region during other studies on diet of birds-of-prey, owls, shrikes (Great Grey Shrike Lanius excubitor and Red-backed Shrike L. collu- rio) and carnivores (Red Fox Vulpes vulpes and European Badger Meles meles). Earthworms were identified by the presence of chaetae, insects by the presence diagnostic remains (head-capsules, forelegs, hind legs, elytrae, wings, mandibles), crustaceans by the presence of the carapace remains, reptiles by the presence of character- istic skin scales (März 1987), birds by presence of feath- ers with reference to März (1987) and Brown et al. (1999). Mammals were identified by the presence of teeth and mandibles and reference to Pucek (1984).