Controlling herbivore insects by insectivorous birds is a major ecosystem service, nevertheless little is known about how local habitat features and forest management influence the efficiency of this service and about how the pest control service birds provide can be maintained and improved. We conducted an experiment in temperate oak forests in the Mátra Mountains, northern Hungary to measure bird predation rate of artificial caterpillars resembling winter moth (Operophtera brumata L.) larvae, to evaluate the relationships among insectivorous bird communities, caterpillar populations and leaf damage caused by caterpillars and to assess the effect of forest heterogeneity on these processes. We found, that structurally heterogeneous forests maintained a significantly higher abundance of insectivorous birds.Especially the tree size heterogeneity increased bird abundance. The rate of bird predation was positively related to the abundance of insectivorous birds as well as to caterpillar abundance, which indicates that birds were able to respond to caterpillar density. We were not able to demonstrate a direct negative effect of bird predation on caterpillar abundance and a positive effect of caterpillar abundance on leaf damage. Structurally heterogeneous forests, however, suffered from less leaf damage than did homogeneous forests, which result may indicates that the higher activity of insectivorous birds in heterogeneous stands resulted in 3 lower activity of insect herbivores. Thus, we concluded that forest management can contribute to the mitigation of insect damages by maintaining the suitability of forest stands to the insectivorous bird communities through the maintenance of high stand heterogeneity and the presence of some key elements (e.g. retention tree groups, tree diversity, shrub layer).

No abstract

Controlling herbivorous insects by insectivorous birds is one of the most important regulating services in forest ecosystems. The fragmentation of forests and the associated increase of edge effect, however, influences forest bird communities and thereby may have an impact on biological control via the modification of prey-predator interactions. In the present study we aimed to examine how insectivorous bird abundance and their predation on artificial caterpillars were affected by forest edges and vegetation structure in fragmented temperate forests of southwest Hungary. We found an unexpected negative humpedshaped pattern for predation rate as well as for bird abundance, having peaks both at the edge and in the interior (50 m from the edge). We found a positive correlation between bird abundance and predation rate, therefore the important role of birds in insect pest control was supported. Interestingly, the abundance of insectivorous birds had negative relationships to forest structure variables, such as tree basal area and tree species richness. This unexpected pattern may be a result of the context-dependency of edge effects that cannot be fully explained by our study. It highlights the need for more studies to explore the general pattern of edge effect on insect pest control.