A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)

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

decaocto gathering in the centre {Bozsko, Juhász, 1981), and the invasion-like appearance of the individuals of Bombycilla garrulus and Corvus frugilegus. 2. Old citycentre (plot: 10 hectares). It is an area that surrounds the town centre, a biotope of internal position, consisting of low-built houses variegated with rows of trees and bushes. In comparison with the town centre there is a change in the ornithofauna, nevertheless the high dominance values are shown here too by the mass-species of the towncentre (Table 2). However, the bird community is poor here both in species- and individual count, in spite of the more abundant vegetation and the relatively lower degree of anthropogenic influence. The abundance values are lowest here in the whole town, at the same time, the very low numerical appearance means a high dominance category (e.g. Hirundo rustica, Phoenicurus ochruros, Passer species). The greater variety of plants shows only the qualitative rearrangement of the bird species, in comparison to the town centre the number of phytophagous and insectivorous species is higher here. The unifacial community is only slightly rearranged by the spring movement of the birds. The average abundance of 18 species is 6 pairs/ha, and this, with the nearly 50% summa D value for Streptopelia decaocto and the two Passer species hardly shows a fauna of ecological value. In the nesting period the ornithofauna of the ancient town-centre gets even poorer. The few species are represented by a number of individuals setting up a "negative record" (4.5 pairs/ha). In the hatching period even the otherwise most common mass species can only be observed in small numbers (Table 2). The prolonged presence of species preferring high buildings is, from the beginning, ruled out by the lack of such structures. When autumn sets in, the minimum individual bird count is manifested. The core of the bird community is constituted now by five ED species (Passer montanus and domesticus, Streptopelia decaocto, Parus major, and the individuals of the already arriving Corvus frugilegus), which, together with the four D species amount to nearly 85% of the bird population (Table 2). The other birds that appear here occasionally (Accipiter nisus, Dendrocopos major, C. coccothraustus) can be regarded as ones making the whole picture more colourful. In cold winters a basic change can be observed in the species composition of the oldtown biotope. The fruit of the hackberry tree attracts the birds coming southward in winter (Turdus pilaris, T. iliacus, Bombycilla garrulus). Simulateneously the departure of some permanently dwelling species can be encountered (Streptopelia decaocto and Passer montanus). Thus, this period is characterized by the preponderance of winter guests and the emigration of other species. 3. Housing estates (plot size 26.5 ha). A biotope characterized by special ecological conditions, which can be divided into areal units subjected to elevated anthropogenic effects, and a "roof level" region, that is, a less disturbed region, interpretable as an independent ecotope. The rubbish and food scrapings on the concrete covering and lawn result in a local abundance of feed. The roof level region is significant as nesting place, as well as an area for rest, observation and for consuming the feed. The ecological factors of the housing estate biotopes demand a bidirectional adaptation and specialization from the bird species. This is manifested in the abundance and dominance values too (Table 3). The fully urban species are members of the housing estate ornithocenose in considerable numbers in all aspects. The abundance of species coming here for feeding increases only in special periods of time. In spring only those species appear in considerable numbers that also nest, here (Streptopelia decaocto

—9.3 pairs/10 ha, Passer domesticus

—11.69 pairs/10 ha). The high adaptational capacity of these two species is indicated by the fact that together they constitute 63.26% of the whole population. It is interesting to mention that the species regarded as 45