Occurrence of nematodes (mostly dominating and common species of Porrocaecum ensicaudatum and P. semiteres) in host populations of birds (Turdus merula, T. philomelos, Sturnus vulgaris and Scolopax rusticola) was summarized in frequency distributions, and tests of agreement with the Poisson model as well as the modified binomial have been computed. Comparisons of the observed frequencies with the expected ones showed the high values (3--257) of the coefficient of dispersion, the so-called "overdispersion", characteristic for the negative binomial which is an extension of the Poisson model. A nearly perfect fitness of the counted (observed) with the expected frequencies was found for S. vulgaris both in the analysis of nematode metapopulation and their common species of P. ensicaudatum. Some deviations from the expectations were found for tracing of all nematode species distributions in T. merula, T. philomelos. On the other hand, the same model (negative binomial distribution according to moment method) has fitted quite well to each for common or dominating nematode species.