The breeding avifauna was studied in the years 1983-1985 in 17 Warsaw parks, 185 ha in total area. The location of the areas in the city has been presented in Fig. 1, and their characteristics in Tab. 1. The aim of the study was to determine changes in the breeding avifauna by comparison with the data from similar researches in the same areas, carried out in the mid-70s, and to establish the influence on the avifauna of the nest-boxes put up in the parks censused. Observations were carried out from the end of March to mid-Julay (5 to 15 in each park, depending on the park area size). Counting was based on the standard mapping method extended by the seeking of large-species nests and addition of data on nest-box breeding. During the three breeding seasons a total of 37 breeding species and 7 probable breeding species (Tab. 2) were recorded. The largest numbers (up to 31) of species were found in large parklands (above 15 ha) with old or medium-aged stands, and the smallest (8-9) in small parklands and parks with young tree-stands. In areas above 5 ha the numbers found ranged from 8 to 9 p/10 ha in „open", young-stand parks, up to 86-89 p/10 ha in old or medium-aged large parks. Data on the composition and long-term variation of the avifauna of the particular parks have been set out in Tabs. 3-5. The amplitude of short-term variations in the composition of the parks studied (Tab. 6) was not big enough (Renkonen's coefficient exceeded 60%) to significantly affect the representativeness of the picture obtained from at least two years' data. It was also possible to define the long-term changes that had taken place since the 1970s. An increase was found of the number of nesting species, on an average by 3-4 in each park. The largest numbers of new species were recorded in young-stand parks. The avifauna was also found to have increased its numbers (on an average by 13-22 p/10 ha/park), mainly due to the use of nest-boxes. The long-term changes listed in Tab. 7 had been caused by the following factors: permanent changes made in the study areas (without using nest- boxes), use of nest-boxes, intensified synurbization of some species. Vegetation changes (most intensive in young-stand parks) and other changes, brought about by man's activity, caused the following species to disappear from the study areas: Perdix perdix, Acrocephalus palustris, Alauda arvensis, Galerida cristata, Motacilla flava, Motacilla alba, Luscinia luscinia, Phylloscopus trochilus, Lanins collurio, Cuculus canorus. Cleaning and barring of large tree-trunk holes in old parks was the cause of a considerable decrease in numbers of Corvus monedula and Sturnus vulgaris in that habitat. Though the area overgrown with bushes had decreased, and the litter layer had been destroyed, no changes could be seen in the numbers of: Hippolais icterina, Erithacus rubecula, Phylloscopus collybita, Phylloscopus sibilatrix, Sylvia atricapilla, Sylvia communis, Sylvia curruca, and the species even sometimes settled in new territories. In most parks there occured a growth in numbers of species nesting in tree tops: Pica pica, Corvus corone, Streptopelia decaocto, sometimes Oriolus oriolus and Columba palumbus. In the years 1983-1985 a total of 750 nest-boxes were put up in the parks censused (Tab. 1). The effect of this practice on the composition of the avifauna was assessed (Tab. 8) on the basis of data for the 1970's, when there were not nest-boxes there. The putting up of nest-boxes had a direct influence by causing an increase in the level of numbers of the avifauna (particularly in new parks). Nest-boxes resulted in the settlement or increase in numbers of the following species: Passer domesticus, Sturnus vulgaris, Parus caeruleus, Ficedula hypoleuca and Passer montanus. The use of nest-boxes has not been found to have a direct influence on the number of those species that do not nest in tree holes. In comparison with tire 1970s, a clear growth was found of synurbized populations of six species, particularly: Turdus pilaris, Turdus merula, Pica pica, Corvus corone, as well as Columba palumbus and Coccothraustes coccothraustes. The process of synurbization of Garrulus glandarius and Turdus philomelos was found to have started, while Anas platyrhynchos and Streptopelia decaocto were found to have increased their numbers.
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