L. Forró szerk.: Miscellanea Zoologica Hungarica 7. 1992 (Budapest, 1992)

Andrikovics, S., Bankovics, A. , Csörgő, T. , Gere, G. , Sass, M.; Török, J.: Hydrozoological characters of a reconstructed wetland

- were found only rarely in their stomach. The major part of their food consists of different mosquitoes in the spring, and of aphids and bugs in the autumn. Most of their prey were not moving or only slowly moving. Out of the vertebrates they consumed only amphibians but even them in small number only. Both R. arvalis and R. esculenta seem to be generalistic opportunistic predators. Their diet at the same time proved to be very similar (Table 2). The rich food supplies made this possible even in the season when the density of the frogs was the highest. Table 2. Percents of dominant food groups oiRana arvalis and R esculenta in both studied areas of Kis-Balaton Date 1987 1988 1988 Oct.-Nov. Apr.-May. Oct.-Nov. Taxon Resc. Rarv. Resc. Rarv. Resc. Rarv. Gastropoda 0.57 1.48 0.99 1.14 0.00 3.60 Isopoda 0.23 1.59 0.66 1.63 0.34 3.60 Diplopoda 0.17 0.63 0.17 0.33 0.00 0.90 Chilopoda 0.17 0.42 0.00 0.16 0.00 0.30 Collembola 1.13 3.07 0.17 1.47 0.68 1.80 Odonata 0.11 0.11 0.66 0.33 0.00 0.00 Orthoptera 0.00 0.21 0.33 0.16 0.00 0.00 Physopoda 0.90 0.32 0.00 0.16 0.00 0.00 Heteroptera 1.24 0.85 0.33 0.98 32.99 18.62 Aphididae 43.19 35.62 0.50 0.65 18.00 10.31 other Homoptera 2.71 4.23 0.00 0.98 4.42 6.01 Coleoptera 5.28 8.56 3.47 11.07 6.80 14.11 Lepid. larvae 3.28 2.43 0.00 3.75 1.70 7.81 Nematocera 10.51 6.45 88.93 61.50 17.35 9.01 Brachicera 11.53 9.83 2.15 3.75 2.72 4.20 Hymenoptera 8.93 9.30 0.99 3.61 8.50 3.30 Araneidea 2.20 3.49 0.50 6.85 3.40 8.11 Acaridea 4.18 5.07 0.00 1.14 2.38 5.11 Vertebrata 0.28 0.00 0.00 0.00 0.00 0.00 other 2.83 6.34 0.17 0.33 0.68 3.30 The reservoir area has a very rich bird fauna, which has been studied since 1984 when the area became flooded in May. Between 1984 and 1988 there were breeding bird species in the area. Among them 56 species part of the former breeding avifauna that was breeding here in the remaining habitat fragments of the former marsland. There were 28 species which were new settlers of the area after it was flooded (Bankovics 1991). The dynamism of the immigration of the Caspian Grebe (Podiceps nigricollis) seems to be very interesting. First this species appeared in very great numbers but later its population decreased gradually. In 1985 the number of breeding pairs was 100, in 1986 150, in 1987 85 and in 1988 only 50. In 1989 this species disappereared from the area. Its breeding was uncertain in the Kis-Balaton area in 1990. The population of one of the other similarly immigrated species, the Whiskered Tern (Chlidonias hybrida), increased between 1985 and 1988, and now this bird is also characteristic of the studied area. The rapid increase of its population has