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

180 NATURA SOMOGYIENSIS ular habitat complexes can also be analysed, and, using quantitative variables and indices derived from basic regular data, changes in the proportions of taxa as well as their trends can be examined. By means of landscape pattern analysis of habitats along Drava, and by applying GIS, small mammal distribution in the area can be interpreted at a landscape ecological scale as well. Owls are important top predators of Cetral-European ecosystems, with the barn owl Tyto alba (Scop., 1769), strictly protected in Hungary, having special importance due to its role in small mammal faunal studies. Because of its significant role in the food chain, and because its behaviour and habitat are closely associated with humans, there have been several studies focusing on its habits, nesting characteristics, breeding biology and ecology (TAYLOR 1994, MIKKOLA 1983), and feeding ecological studies dealing with the barn owl as a predator provide important data concerning prey species as well. Indirect monitoring based on barn owl pellet analysis provides information about the composition and structure of small mammal communities using the mosaic-pattern hunting areas surrounding particular nesting sites. (SCHMIDT 1973, WIJNANDTS 1984). Habitat patches differing in their sizes determine the local densities of small mammal populations found there, and the higher percentage of small mammals in various patches are represented in barn owl food as well, however these correlations can become clearer if areas analysed are larger (HORVÁTH et al. 2003). River Drava being a green corridor in the south of Hungary, is an important conservation area, with lowland areas along the river being inhabited by dense barn owl populations. Regular pellet collecting has been done in these areas, and their data are used in anlyses of spatial and temporal distribution of small mammals. In the present study monitoring data from the upper river section (Somogy county) are ivestigated together with barn owl pellet data. Correlations were analysed between landscape patterns of barn owl nesting areas and the compositions of small mammal communities shown in barn owl pellets, as well as we looked at statistical differences in the feeding ecology between owls nesting in Drava Lowland areas that differ in their patch compositions. We have performed regular pellect collecting in barn owl nesting areas of the Drava Lowlands, and based on their spatial distributions three larger regions were differentiated. Landscape ecological and small mammal faunal data of these regions were summed and evaluated on a larger spatial scale and on the local hunting area scale as well. Answers were sought to the following questions: (i) are the patch compositions of the larger designated areas similar to the hunting areas of the barn owls, thus can we draw conclusions for the small mammal composition of the entire area, (ii) what are the differences between the Drava sections in their food and patch compositions, (iii) are the differences in patch compositions of the different-scale areas expressed also in the food compositions of barn owls in those areas, or how does patch composition determine the type of small mammal fauna shown during monitoring? Material and Methods A total of 17 barn owl nesting locations were selected along river Drava, so that small mammal communities indicated from owl pellets can be analysed based on the landscape ecological investigation of the owls' hunting ranges. Nesting locations were compared based on both owl feeding data and vegetation patch composition. The first sampling period in the selected nesting sites lasted during the first nesting period, from spring to late June. The second sampling period lasted from August to