Common kestrels (Falco tinnunculus) and longeared owls (Asio otus) in intensively farmed areas in Switzerland decreased markedly as a result of declining vole (Microtus spp.) populations. In order to counteract the loss of biodiversity in intensively farmed areas, the Swiss agri-environment scheme stipulates several types of ecological compensation areas, which together should take up 7% of the farmland. Among them are wild flower and herbaceous strips, which are not mown every year and which in summer support up to 8 times more small mammals than ordinary fields and grassland. This study investigates whether kestrels and long-eared owls preferentially hunt on ecological compensation areas and whether preferred hunting areas are related to the density of small mammals or to the density and height of the vegetation. Both kestrels and long-eared owls mainly hunted on freshly mown low-intensity meadows and artificial grassland, despite low densities of small mammals. Therefore, vegetation structure was more important for the selection of hunting sites than prey abundance. However, both predators preferred to hunt on freshly mown grassland and meadows bordering a wild flower or herbaceous strip. Voles from these strips probably invaded the adjacent freshly mown grassland and became an easy prey for kestrels and owls. In intensively farmed regions, ecological compensation areas, particularly those not mown each year, are an important refuge for small mammals, although in summer the small mammals are not directly accessible to hunting birds. Hence, a mosaic of different habitat types with grassland mown at different times of the year together with undisturbed strips is best suited to provide a year-round supply of accessible food for vole hunters.

Small mammals make up an important link in the food chain as many predator species feed on them. There are indications that small mammal populations in Europe are declining due to the intensification of agriculture. According to national legislation, farmers in Switzerland have to cultivate at least 7% of their land as ecological compensation areas and, thus, some alternative habitats that are possibly beneficial for small mammals have been created. In this study, we estimated the diversity and density of small mammals on two types of conventional farmland field types (artificial grassland and autumn-sown wheat) and three types of ecological compensation areas (wild-flower strips, herbaceous strips and low-intensity meadows) by use of capture-recapture in March, May and July 2003. The common vole Microtus arvalis was the most abundant and predominant species in all habitat types except in herbaceous strips, which harboured the highest diversity with six species caught. In March the density of small mammals was generally very low, but significantly higher in wild-flower (mainly due to common vole) and herbaceous strips than in the other habitat types. In wild-flower and herbaceous strips, densities increased strongly from March to May and in July. On autumn-sown wheat fields, a strong increase occurred only from May to July and was caused by common vole. On artificial grassland and lowintensity meadows, densities of small mammals (mainly common vole) increased only marginally with low-intensity meadows supporting slightly higher densities. Thus, habitats that were not mown each year supported the highest densities of small mammals. This demonstrates that ecological compensation areas, such as wild-flower and herbaceous strips, make up an important refuge for small mammals. They probably also have positive effects on populations of many predator species that depend on small mammals, particularly if a mosaic with mown surfaces is created.

No abstract

No abstract