A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)

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

For the lack of space this paper will not be concerned with the summer period, since this one is less significant in the life cycle of birds. In the elaboration of the material the following markers were established: abundance (A), dominance (D), dominance identity (Renkonen index), species diversity (H

s

) and evenness (J). The calculation of diversity was performed with the Shannon-Wiener function Hc= — 2 —- • m

~- where n n H

s is the value of species diversity, — is the dominance of the i

th species. Evenness was calculated with the formula: ln

s where J is the value of evenness, In S is the maximum species diversity, and H

s is the total number of species (Legány, 1982; Török, 1984). The calculation of the Renkonen index (Re) was performed with the method of Balogh (1953). Quantitative analysis of urban bird communities a) Seasonal aspects of bird communities 1. Town centre (plot 12.5 hectares). The species and inividual bird counts are small in this busiest and most highly utilized area of the town in all aspects. Only 26 species can be demonstrated for the whole year, which is 28% of the whole ornithofauna, however, there are only 9 of these that breed and 17 that feed here (Table 1). The decisive in the composition of the bird communities are the species that "as fully urban" (Bozsko, 1971) are on the top level of urbanization (Streptopelia dacaocto, Passer montanus et domesticus, Columba livia domestica). These are only complemented by some characteristic species of the summer and winter periods. The essence of the town-center bird population is constituted by the eudominant (ED) and dominant (D) species for which summaD=77.2%. The number of species and individuals of the spring aspect is partly determined by the species featuring as winter guests (Corvus frugilegus, Bombycilla garrulus), on the other hand, the ornithofauna is made more colourful by some species that come early (Phoenicurus ochruros, Hirundo rustica, Delichon urbica). In the nesting period there is a further decrease in the species count of the communities of anyway slight ornithological value. The summa D value of the four ED species is nearly 80%, and hardly 20% for the remaining 8 species. In spite of all this the dominance values are high for most of the species present (D and subdominant, SD, groups), which indicates the stability of the population. The value of abundance reaches 7.3 pairs/ha in the towncentre in the nesting season. The above-mentioned composition of the fauna gets somewhat changed in the autumn months (Table 1). The abundance of the migratory species drops, the individuals of the common mass species make their way to the innermost spaces of the town, and the autumnal wandering species also appear (Parus major and caeruleus, Carduelis chloris, Erithacus rubecula). In cold winters the total abuncance is essentially higher

—it reaches a maximum as compared to the whole year (11.9/ha). This is mainly due to the flocks of Streptopelia 44