A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)

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

The cold winter brings obvious changes in the dominance identity values (Fig. 1). The absence of migratory species decreases, from the outset, the number of potentially comparable species, thus, the lower species count may give rise to differences of an order of magnitude between the particular biotopes. The only exception is the fauna of the Great Forest

—Public Cemetery zone, which is characterized by high species identity even in the winter period (71.68%). The 71.47% similarity in the Garden City and the industrial zone can be accounted for by the mostly identical proportion of the D values of the wintering guests of similar species. There is an extremely poor connection between the town centre, concentrating a few mass species, and the significant wintery ornis of the Cemetery (15.47%) and the bird community of the Great Forest (16.02%). DISCUSSION The town of Debrecen can be divided into ecologically different areas, each of which is characterized by special bird communities. On the grounds of the richness of species, the stock density, diversity and evenness values a good distinction can be made between the bird populations of the built-up urban districts (town centre, old city centre, housing estates, industrial zone) and the green areas (small urban parks, Great Forest, Public Cemetery, Garden City) as well as the outskirts forming transition to the suburban zone (Fig. 2). In the districts built up with administrative, commercial and residential buildings, which constitute about 3

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4 of the area of the town, 12-15 breeding species can be found, the abundance of the bird population does not exceed, together with the mass species, 2.2-7.3 pairs/ha, and the species diversity means are lowest for the whole town (1.6418-2.2556). The group of ED and D species consists primarily of nesters of cavities and buildings, such as Streptopelia decaocto, Columba livia domestica, Delichon urbica, Hirundo rustica, Passer domesticus and montanus. In the old city centre these are complemented by Turdus merula and Carduelis carduelis, in the housing estate by Sturnus vulgaris, in the industrial belt by Phoenicurus ochruros and Chloris chloris. The high J value registered in the industrial belt (0.9077) indicates the nearly maximum possible utilization of the ecologically poor biotope. The nesting bird communities of the green areas stand an order of magnitude higher both in species and individual count, according to each marker. The species count is 30-40, the mean of A is 10-20 pairs/ha, in the small parks it may reach 46.6 pairs/ha. In consequence, the H

s values are also higher (2.74-3.09) and indicate a varied fauna. The group of D species is much smaller and more heterogeneous as compared to the central areas, and apart from Streptopelia decaocto, consists primarily of forest-dwelling species: Parus major (Great Forest), Turdus merula, Philloscopus collybitus, Sturnus vulgaris, Carduelis chloris, Fringilla coelebs (Cemetery). In the case of the given green areas it was not possible to find an unequivocal linear connection between the quantity and level distribution of the vegetation and the values of species diversity. A trend can be observed in the increase of the richness of the fauna from the smaller green areas towards the large parks, however, this regularity (Elvers, 1978, Lancaster, Rees, 1979) can only prevail in its pure form in biotopes of identical class, e.g. in parks (Elvers, 1978, Sasvári, 1981). The diversity values of the built-up green areas, such as the Green City, are modified by the degree of coverage by buildings and the pressure of civilisation. This accounts for the H

s values and the fluctuations of A in this biotope group (Fig. 2). Thus, in the belt of the houses with gardens (Garden City), where the vegetation is more sparse and less varied, the diversity value is higher than in the small parks, which are made more attractive for the birds not only by the varied vegetation but also the surrounding buildings, which together result in a large bird population (See Table 10, Fig. 2). 52