A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)

Természettudomány - Juhász, Lajos–Bozsko, Szvetlana: The Ornithofauna of Debrecen II. Synecological Analysis

the increase in species count (35). The transitory species appear again in nearly identical composition, but in somewhat smaller groups. The area is populated by numerous species in the winter season too. Nearly all wintering species appear in the small parks, some of them in striking individual numbers (Turdus pilaris—

4 pairs/ha, Bombycilla garrulus 6 pairs/ha, Passer domesticus 13.6 pairs/ha). In view of dominance distribution the species can be divided into two large groups. The ED, D and SD categories involve altogether 14 species. Lower individual numbers are characteristic of 16 species, but, which is a characteristic of the wintering bird communities, they can be observed nearly continuously (Table 6). 7. Great Forest (plot size: 10 hectares). A highly utilized park area, which is contiguous with the forest areas outside the town. This connection has proved to be a decisive factor in respect of the ornithofauna in the intraurban territory of the Great Forest. Thediffereciated vegetation, the feeding and watering places afford ideal conditions to a great number of species. On the annual level the richness in species is greatest (64 species) in the Great Forest within the whole town (Table 7). This is about 70% of all species observed in the town. The 37 nesting species constitute 56.66% of the total nesting fauna. The bird movement in the spring season results in a varied species composition. The winter and spring migrations overlap each other, which is manifested in the high abundance values (19.9 pairs/ha). It is of special value for the ornithocenose that out of the mass species Passer, only the Passer montanus is eudominant. In the nesting period the individual count reaches its peak. Nearly all species of the total taxonomical spectrum of the town's bird population are nesters in the Great Forest. The increase in the population of the species emigrating from the centre areas of the town, especially Streptopelia decaocto and Passer montanus, which are driven out for lack of nesting place can be observed. Other species also stay in the intraurban area of the Great Forest in individual counts determined by the breeding and species competition present in the natural forest biotopes. At the beginning of summer there is an increase in the dominance of the wandering species (Parus sp.), in other groups there is some decrease. Contrary to this, species composition shows further differentiation (Table 7), and the number of species appearing is highest now (44) on the annual level. In winter the invasional species (Turdus pilaris, Bombycilla garrulus, Fringilla montifringilla) appearing in hard colds, and some rare wandering ones (Dryocopus martius, Picus canus) complement the temporary winter association. The number of species continues to be significant (34) as compared to the whole town, but the dominance of some species is diminished. The low individual count of Passer and Streptopelia decaocto must be stressed, because they rather spend the winter in the warmer town centre. A high individual dominance is attained in the Great Forest mainly by the permanently staying Parus species (P. major —17.63%, P. caeruleus—

4.86%, P. ater—

4.86%) as well as the flocks of Corvus frugilegus and the invasional species. 8. Public Cemetery (plot size: 13 ha). Being an area taken out from the Great Forest it is an old park biotope. Its independent biotopic status can be explained by some pinegrown areas and favourable ecological factors involving slight athropogenic use. Thus, the ornithofauna of the cemetery is qualitatively independent, but is, at the same time, complement to the Great Forest fauna. In the analysis of the particular aspects the richness of species and maximum abundance of the spring and autumn periods become apparent (Table 8). The spring spectrum of species shows the characteristics of a natural oakwood, with the high degree of niche utilization of the particular species groups. The species typical of urban areas only reach a modest degree 48