A Debreceni Déri Múzeum Évkönyve 1986 (Debrecen, 1987)

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

Lajos Juhász—Svetlana Bozsko The Ornithofauna of Debrecen II. SYNECOLOGICAL ANALYSIS The present study is the continuation of our previous communications {Bozsko, Juhász, 1983, 1984). In the first part of the work the qualitative investigation of the present day ornithofauna of Debrecen and the analysis of the historical changes in the local bird population were performed. On the pages of this work the evaluation of the quantitative characteristics of the ornithofauna is presented. Material and methods The quantitative investigation of the ornithofauna took place between September 1, 1981 and April 30,1983 {Juhász, 1983). The more detailed elaboration of this work, expanded with a wider theoretical aspect, is published first in this study. Owing to the limited size of the volume we will not repeat here the general description of the town and the particular methodological details, which were discussed in the previous publication, here we will touch upon only the questions involved in the present topic. The counting of the birds was performed according to the biotopes on the plots, twice every month on average, which in the course of two years amounted to 47 counts for each plot. The size of the plots usually exceeded an area of 10 hectares, however, for objective reasons there were smaller ones, too, e.g. in the case of small parks and on the outskirts of the town. The data are discussed as averaged for two years, considering the seasonal aspect. An exception was made for the winter season, which had to be analysed separately, since the winter of 1981/82 was colder and snowier than usual, whereas the winter of 1982-/83 was warm and of Mediterranean character, which considerably influenced the species composition and the bird count. In view of the shortage of space only the data for 1981/82 will be analysed in the study, since they reflect the winter ornithofauna of Hungary more realistically. The seasonal aspects for an urban bird population were determined as follows

: a) The period of spring migration: from the middle of March to the second half of April, i.e. the time of the movement of birds early in spring. b) The nesting period: from end of April to end of June, the actual hatching period of urban species. In this period most species complete the bringing up of the first brood. c) The summer period: from the end of June to middle September. It is characterized by the second hatch of some species, wandering with the young in the case of other species, there is a major rearrangement of species in this time. d) Autumn period: from the second half of September to the middle of November. Migration is opposite to that of the spring aspect. It is marked with the appearance of somel wandering species. e) Winter period: from the middle of November to the middle of March. 43