© Markus Jenny
Long-eared owls, kestrels and ecological compensation areas
What is the importance of small mammals in ecological compensation areas as food source for long-eared owls and common kestrels?
Long-eared owls and common kestrels primarily feed on small vole species, in Switzerland mostly on the field vole (Microtus arvalis). In intensively managed farmland, field voles have become rare. There is evidence that field voles reproduce better in ecological compensation areas, particularly in herbaceous and wildflower strips and extensively used meadows, than in intensively managed farmland. Thus, ecological compensation areas may provide a good food source for vole-eating species. In the Wauwil plain, the following questions were investigated in a Master thesis:
Are the densities of field voles and other small mammal species higher in wildflower strips and/or exensively used meadows than in the surrounding crops? Does the long-eared owl use the ecological compensation areas as foraging sites? Are prey species used according to their availability? What influence does the crop harvest have on the field vole population? Are ecological compensation areas used as retreats by field voles during the harvest period?
In collaboration with local farmers, the Swiss Ornithological Institute has started in 1995 to create ecological compensation areas in the Wauwil Plain. The implemented measures mostly consisted of wildflower strips and extensive meadows. We set live traps for small mammals in the ecological compensation areas and in adjacent fields. Additionally, we observed where and how often kestrels and long-eared owls hunted for prey.
The long-eared owl and the kestrel are two priority species of the Swiss species recovery programme for birds. The lack of food caused by intensified agriculture is considered one of the major reasons for the population declines. Therefore, it is important to increase our knowledge on the species´ foraging behaviour, particularly in intensively managed farmland.
This project points out the role of ecological compensation areas along the food chain, from wildflower seeds to small mammals to birds of prey, such as the long-eared owl and the kestrel. It delivers solid arguments for an increased ecological improvement of cultural landscapes.
The highest densities of small mammals were found in wildflower and herbaceous strips. In artificial grassland and extensive meadows, however, only few common voles and other small mammals were caught. Contrary to our expectation, long-eared owls and kestrels did not prefer the areas with high densities of small mammals but hunted primarily on freshly mown artificial grassland and extensive meadows. The most preferred hunting sites were freshly mown areas adjacent to wildflower and herbaceous strips. Presumably, small mammals, which left the cover in the strips to roam across open fields, were easy prey for the raptors. Therefore, wildflower and herbaceous strips appear to have an indirect, positive effect on kestrels and long-eared owls.