Stable Isotope Analysis Supports Omnivory in Bank Voles in Apple Orchards

With only periodic and incomplete studies of its diet over time, all with differing methods and conclusions, the degree of omnivory in the bank vole ( Clethrionomys glareolus ) is not fully clear. We assessed the trophic niche of the species using isotopic ( δ 15 N and δ 13 C) compositions from hair samples and analysed how C. glareolus shares trophic space with herbivores, granivores and insectivores living syntopically. According to the numbers trapped, C. glareolus was the fourth most numerous species in the apple orchards that we investigated, accounting for 14.4% of all trapped small mammals with a relative abundance of 1.12 individuals per 100 trap nights. The average values of both δ 15 N and δ 13 C in the hair of C. glareolus differed from the other trophic groups, with the average of δ 15 N in orchards and neighbouring habitats (6.55–6.95‰) being closest to that of insectivores. Intraspecific trophic niche differences (depending on age, gender and reproductive status) were not expressed, while correlations between body mass, body condition index and both δ 15 N and δ 13 C values were not consistent. In comparison to analysed basal resources, isotopic signatures in the hair were closest to the values in invertebrates and apple seeds. The degree of omnivory in C. glareolus was not the same in different habitats. This may be an indication of ecological plasticity within the species, allowing its inclusion/success in multi-species small mammal communities.