Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)

Horváth, Győző, Molnár D., Németh Tamás - Csete Sándor: Landscape ecological analysis of barn owl pellet data from the Drava lowlands, Hungary - A Dráva menti gyöngybagoly köpetekből nyert adatok tájökológiai elemzése

HORVÁTH ET AL.: ECOLOGICAL ANALYSIS OF BARN OWL PELLET DATA 187 Fig. 6. Correlation between patch diversity and species number analysis is applicable for the landscape-scale characterization of small mammal communities and their habitat vegetation patches. In our earlier study we also looked at how prey diversity changed in relation to certain distinguished patches. Patches that are less optimal for the barn owl cause lower species diversity, which was expressed in the case of local hunting areas mostly by the higher rate of inner areas of human settlements. Thus it was concluded that in settlements with higher proportions of inner areas the small mammal community shown from pellets is less diverse. Another important relationship was revealed for forest patches, too: as the percenmtage of this patch type grew, species diversity followed an exponential function (HORVÁTH et al. 2003). As patch size grows, its perimeter grows at a smaller rate, but in this patch it is the perimeter, i.e. the edge zone that acts as potential hunting area for the owl, where, by preying upon forest species, its prey composition becomes wider. As forest size grows, the number of species that can be caught will not grow further, meaning that in patch with a certain ratio of area/perimeter all the potentially hunted species will be represented in the food. Larger forest patches than this size will not cause higher species diversity; it is rather the smaller, separated forest fragments that can be beneficial for the barn owl, as these are the ones that have higher area/perimeter ratios, i.e. larger forest edge proportions. A correlation revealed in the present study for bank vole occurrence in the Drava sections has provided new information for the evaluation of forest patch proportions. Similarly to the issue of diversity, it was presumed that there is exponential or logarithmic correlation between the frequency of the bank voles and increasing numbers of forest patches, meaning that above a certain amount of forest the quantity of bank voles indicated by pellets will not be considerably higher, due to the fact that the barn owl does not hunt in closed forests. However, a linear correlation occurred between wooded areas and relative abundance values of this species, which suggests that a higher fragmentation of forests along river Drava means a high ratio of perimeter/area providing higher chances for the owls to successfully hunt for bank voles inhabiting forest edges. Based on patch overlap calculations and homogeneity tests of patch composition, small mammal faunal data of smaller localities can be cumulated and, in the case of our sampling areas along river Drava, can be evaluated on landscape ecological scales much larger than the actual hunting ranges of barn owls.