A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)

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

of abundance. The list of the dominant (Parus major, P. caeruleus, Turdus merula, Carduelis chloris, C. carduelis) and subdominant species reflects the potential of the biotope. The niche segregation among the 38 species observed here is even, the association has a high species diversity. Another stabilization of the community is brought by the arrival of the actual nesting period, with the dominance of the species of Paridae, Turdidae and Fringillidae, which show high D values. Dominant among the nesters are the dendrophilous species (14 species, 45.16% of all nesters). The autumn period is associated with a considerable mobilization of species, qualitative and quantitative rearrangement. A number of rare wanderers intrude into the Cemetery (Accipiter nisus, Phasianus colchicus, Dendrocopos medius). Parallel to this, the abundance of migratory species is falling and they are gradually replaced by the species coming down from the north and wintering here (Corvus fragilegus, Turdus pilaris, T. viscivorous, T. iliacus, Pyrrhula pyrrhula). Compared to the value of the 8 D nesting species (51.1%), in autumn there are only 3 D species and the summa D value is only 16.7%. The winter period is characterized by the preponderance of the permanent species (Paridae, Fringillidae) completed with members of the Picidae and Corvidae families. It is especially the pine groves that constitute an enriched biotope due to the good conditions of feeding and rest. 9. Outskirts of the town (plot size: 3 ha). This is a biotope forming transition to the out-of-town areas, thus its structure is extremely heterogeneous. The species- and individual counts are significant, the distribution of species is less differentiated (Table 9). There appear rare species, which do not enter the central parts of the town (Alauda arvensis, Lullula arborea, Anthus triviális). Decisive in the species composition is the group consisting of the common bird species of the town (Streptopelia decaocto, Passer sp., Turdus merula, Carduelis carduelis). Missing are, however, the species which are typical dwellers in the town centre, and definitely prefer the high buildings (Apus apus, Columba livia domestica, Tyto alba). A rearrangement similar to the other biotopes can be observed here too, in the spring period. There are, however, some characteristic features. The D (10.7%) and A (40 pairs/10 ha) values are extremely high for Sturnus vulgaris which migrates in flocks. Migration also shows its effect in the case of other species, too (Hirundo rustica

—23 pairs/10 ha, Luscinia megarchynhos

—13 pairs/10 ha, Anthus triviális—13 pairs/10 ha, Lanius collurio

—10 pairs/10 ha). On the other hand, the individual count of Streptopelia decaocto is surprisingly low, at this time the larger part of the urban population still stays in the internal districts. In the nesting aspect there is a change in the dominance of several species. Streptopelia decaocto appears as a D species (7.7%), Sturnus vulgaris only shows a SD level (4.42), whereas Turdus merula is nearly ED (8.84%). The difference in the populations of Passer domesticus and P. montanus is surprising again. The different ecological demands of the two Passer species can be well demonstrated in this zone. Passer domesticus is more faithful to the inner part of the town in nesting than P. montanus. Characteristic of the autumn period is rapid migration and the appearance of several wandering species. Two species of owls (Athene noctua, Strix aluca) extend their hunting ground to the outskirts of the town, but Accipiter nisus is also present. The second half of the autumn is decisively the period for the appearance of Corvus frugilegus (58.33 pairs/10 ha). Out of the wintering guests relatively few stay on the outskirts. They usually remain in the urbanized environment and only a few of their species use the outskirts for prolonged feeding (Bombycilla garrulus, FringiUa montifringilla, Carduelis chloris). Thus, the area —contrary to other biotopes

—yields low species- and individual counts in winter, emphasising by this the bird-accumulating role of the central zones. 49