Distribution of Four Vole Species through the Barn Owl Tyto alba Diet Spectrum: Pattern Responses to Environmental Gradients in Intensive Agroecosystems of Central Greece

SIMPLE SUMMARY: Voles of the genus Microtus represent one of the most speciose mammalian genera in the Holarctic. Moreover, they are also widespread in the European agricultural landscape. In addition, they are the most common vertebrate pests in European agriculture, causing extensive annual damages to a large variety of crops and exposing humans to an increased risk of pathogen transmission. In order to propose mitigation and possible management measures, it is necessary to record the initial abundance and distribution patterns of vole species within complex ecosystems. Considering the large extensions occupied by agroecosystems and the demanding but small-scale application of live trapping, an optimal method to initiate small mammal monitoring on large spatial scales is through Barn Owl Tyto alba diet analysis. Barn Owls prey almost exclusively on small mammals and predominantly on voles; thus, they can be used as an ideal proxy for the distribution and abundance patterns of small mammals in the field. In our study, we studied the diet of Barn Owls over a total range of 3000 sq. km for two continuous years through pellet analysis (more than 10,000 pellets) and identified the distribution and abundance patterns of four vole species with respect to different environmental gradients. ABSTRACT: Voles are the most common vertebrate pests in European agriculture. Identifying their distribution and abundance patterns provides valuable information for future management. Barn Owl diet analysis is one of the optimum methods used to record small mammal distribution patterns on large spatial scales. From 2003 to 2005, a total of 10,065 Barn Owl pellets were collected and analyzed from 31 breeding sites in the largest agroecosystem in Greece, the Thessaly plains. A total of 29,061 prey items were identified, offering deep insight into small mammal distribution, specifically voles. Four discrete vole species (Harting’s vole Microtus hartingi, East European vole Microtus levis, Thomas’s pine vole Microtus thomasi, and Grey dwarf hamster Cricetulus migratorius) comprised 40.5% (11,770 vole prey items) of the total Barn Owl prey intake. The presence and abundance of the voles varied according to underlying environmental gradients, with soil texture and type playing a major role. M. levis showed no significant attachments to gradients, other than a mild increase in Mollisol soils. It was syntopic in all sites with M. hartingi, which was the dominant and most abundant small mammal species, preferring non-arable cultivated land, natural grasslands, set-aside fields, and fallow land. M. thomasi was strictly present in western Thessaly and strongly associated with a sandy-clay soil texture and Alfisol soils. C. migratorius was the least represented vole (162 items), exclusively present in eastern Thessaly and demonstrating a stronger association with cereals, Mollisol soils, and an argillaceous-clay soil texture. This is the first study in Greece at such a large spatial scale, offering insights for pest rodents’ distribution in intensive agroecosystems and their response to environmental gradients including soil parameters.