The aim of this work was to investigate the diet of the Tawny Owl (Strix aluco) in NE Poland. Pellets were collected in the territory of one owl in the centre of the Romincka Forest twice a year, in spring and autumn, from 2000 to 2003. Among 450 identified prey items, rodents (38% of prey items), amphibians (34%) and insectivores (17%) constituted dominant groups. Birds were caught only occasionally (5%). Significant differences were found in the diet composition between the two seasons. Birds and insectivores were hunted more frequently in winter and spring, whereas the proportion of murid rodents and amphibians in the diet was higher in the summer-autumn period. The percentages of microtines found in the pellets were comparable between the two seasons. Amphibians preyed on in winter and spring had thicker femurs than those caught in summer and autumn.
The aim of the study was to investigate species composition of the small mammal community of the Romincka Forest (NE Poland) with the aid of the tawny owl Strix aluco as a material collector and to estimate the efficiency of the methods applied. In total, 1209 small mammals were sampled, 909 of which were classified as belonging to one of the 15 species identified. Using the rarefaction method we assessed that in order to record 95% of all the mammal species present, 434 individuals randomly selected from the whole material need to be sampled (i.e. 47.7%). The estimation of the total species richness indicated that all species inhabiting the forest under study were recorded. For two less common mammals, the common pine vole Microtus subterraneus and the common dormouse Muscardinus avellanarius, we made an attempt to calculate the number of animals annually killed by the tawny owl population. Our calculations were based on the proportion of small animals in owls' diet and the density of these birds of prey. We estimated that the tawny owl population removed from 1336 to 2305 individuals of M. subterraneus and from 604 to 1041 individuals of M. avellanarius in the study area every year (i.e. 22.3-38.4 and 10.1-17.4 individuals per km 2 , respectively). Such analysis may be applicable to other rare species, and therefore may be an effective tool for the assessment of biological resources and their conservation planning.
Woodpecker diversity is usually higher in natural forests rich in dead wood and old trees than in managed ones, thus this group of birds is regarded as an indicator of forest biodiversity. Woodpeckers excavate cavities which can be subsequently used by several bird species. As a consequence, their abundance indicates high avian abundance and diversity in forests. However, woodpecker-made holes may be also important for other animals, for example, mammals but it has seldom been investigated so far. Here, we examine how well one species, the Great Spotted Woodpecker, predicts species richness, occurrence and acoustic activity of bats in Polish pine forests. In 2011 we conducted woodpecker and bat surveys at 63 point-count sites in forests that varied in terms of stand age, structure and amount of dead wood. From zero to five Great Spotted Woodpeckers at a point-count site were recorded. The total duration of the echolocation calls during a 10-min visit varied from 0 to 542 s and the number of bat species/species groups recorded during a visit ranged between zero to five. The local abundance of the woodpecker was positively correlated with bat species richness (on the verge of significance), bat occurrence and pooled bat activity. The occurrence of Eptesicus and Vespertilio bats and Nyctalus species was positively related with the abundance of the Great Spotted Woodpecker. The activity of Pipistrellus pygmaeus, Eptesicus and Vespertilio bats and a group of Myotis species was not associated with the woodpecker abundance, but echolocation calls of Nyctalus species, P. nathusii and P.pipistrellus were more often at sites with many Great Spotted Woodpeckers. Moreover, the probability of bat presence and the activity of bats was generally higher shortly after dusk and in middle of the summer than in late spring. We suggest that the observed correlations can be driven by similar roosting habitats (e.g., woodpeckers can provide breeding cavities for bats) or possibly by associated invertebrate food resources of woodpeckers and bats. The abundance of Great Spotted Woodpecker seems to be a good positive indicator of bat species richness, occurrence and activity, thus adding a group of relatively cryptic forest species that are indicated by the presence of the Great Spotted Woodpecker.
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