The possibility of application of Sorensen and Renkonen indexes in the study of winter avifauna in small plots of the urban green areas

Quantitative studies of winter avifauna (1999/2000) were conducted in three fragments of urban green areas in central Poland. Two observers independently controlled three plots six times, doing two subsequent counts (10 ha/1.5 hour) on the same day. All visits that were carried out in the same plot by the same observer during the same time of day were defined as a "survey". Differences between maximum and minimum values of similarity in species composition (Sørensen index - QS) and dominance structures (Renkonen index - Re) between two plots during all "surveys" ranged from 8.4 to 11.9% (QS) and from 11.8 to 22.4% (Re). Coefficients of variation (CV) for values of Sørensen and Renkonen indexes obtained for similarity of winter avifauna between two plots during all "surveys" ranged from 4.9 to 7.6% (QS) and from 8.9 to 14.1% (Re). Significant differences were found in one case between values of similarity in species composition (QS) obtained by two observers between two different plots (Mann-Whitney test, U = 0.0, n = 8, P = 0.02). The results show that there is no possibility to estimate clearly the similarity of dominance structure (Re) and, to a lesser degree, species composition (QS) of winter avifauna between two small fragments of the urban green areas.