Samas, A. and Ulevičius, A. 2015. Eurasian Beaver Building Activity Favours Small Mammals Common for the Forest. Baltic Forestry 21(2): 244-252

Beaver-built structures, such as beaver lodges, can be regarded as specific environment infrastructure components that are supposed to be important to a number of species due their morphological, topographical, microclimate, and temporal features. We have compared the species composition and trapping success of small mammals as well as inter-annual and seasonal variation of these parameters on beaver lodges and in the forest to find out the significance of beaver lodges for small mammals common for the forest. The forest proximity factor was also tested on influence on trapping success of these mammals. The study was carried in hilly landscape of Eastern Lithuania in 2007 – 2012.The mean density of beaver sites was 20 pcs. per 1000 ha. Small mammals were sampled using snap traps on beaver lodges and in the forest once in a season four times a year.

Small mammals of eleven species were caught on beaver lodges (Shannon’s H’= 1.14) and small mammals of 5 species in the forest (Shannon’s H’= 0.74). The typical for the forest bank vole (Clethrionomys glareolus) significantly prevailed over other species on beaver lodges. The stenotopic yellow-necked mouse (Apodemus flavicollis) and eurytopic common shrew (Sorex araneus) were the subdominants on beaver lodges. The trapping success of small mammals on beaver lodges and in the forest has increased from spring to autumn with some depression in winter. In summer, autumn and winter, the overall trapping success of small mammals was significantly higher on beaver lodges than in the forest. This was also true for bank vole and common shrew but not for yellow-necked mouse, which was more successfully trapped in the forest in all seasons. Inter-annual variation of trapping success of small mammals was more expressed in winter in both habitats. Common shrew and yellow-necked mouse showed higher inter-annual variation on beaver lodges, whereas bank vole – in the forest. In autumn, the trapping success of small mammals of three species on beaver lodges was not statistically significantly influenced by the forest proximity factor. However, for the bank vole, the negative correlation between the trapping success and the forest proximity was more clearly expressed and being close to the significance level (p=0.055).

Keywords: Beaver lodges, forest habitat, small mammals, Castor fiber, Clethrionomys glareolus, Apodemus flavicollis, Sorex araneus