Bird populations and their adaptation to environmental changes in the area of the hydroelectric power structures Gabcikovo

In 1994 we were observing changes in the occurrence of water-fowl and birds of prey representatives (Falconiformes) in the region of the hydroelectric power structures Gabcikovo in the section of the Hrusov water reservoir and the adjacent part of the old river-bed of the Danube. In the period from March to August, 1994 fifteen field observations were made, with the use of ordinary audio-visual methods, and the occurrence of 52 species of birds of the above groups was recorded. The preliminary results suggest that the rise of a wide-spread water surface in the immediate neighbourhood of the old river-bed of the Danube gave rise to biotopes suitable for many species of birds. We observed the shifting of one part of the water-fowl from the old flow of the Danube to the water reservoir, with a considerable growth of numbers of individuals, while even the species not typical for the Danubian area before the construction of the hydroelectric power structures appear in abundant numbers. Besides, we observed the occurrence of several species that are rare in our country. The overall numbers of birds found in the observed area amounted from approximately 1400 to 1800 pieces in March to approximately 17000 pieces in August. Further, it was observed that the changes in the water-level of the reservoir have a considerable impact on the dislocation of birds and the representation of individual species. On the basis of the obtained results it is possible to state that the hydroelectric power structures Gabcikovo has become an important place of hibernation for the hibernating species, a place of nesting for the nesting species, and a place for the species finding food in the water reservoir. With a view to the above facts and the excellent opportunity to document the settlement of the newly built water reservoir by the water-fowl , we consider necessary to continue in the research and to concentrate on observation of behavioural changes of the most important species, due to adaptation to newly-formed life conditions. (authors). 3 tabs., 8 refs