Vole pests in apple orchards: use of presence signs to estimate the abundance of Arvicola terrestris cantabriae and Microtus lusitanicus

The sustainable management of vole populations to reduce crop damage requires a reliable estimation of rodent density. The present study was conducted in 2011 in Asturias (NW, Spain) and aimed at developing a method for estimating the density of the water vole Arvicola terrestris cantabriae and the Lusitanian pine vole Microtus lusitanicus in apple orchards based on their presence signs. Previously, as A. t. cantabriae and the Iberian mole Talpa occidentalis occur simultaneously in the same habitats, we had to determine if earth mounds caused by these two species may be accurately differentiated. The results showed that presence signs may be used to discriminate the occurrence of A. t. cantabriae and T. occidentalis in areas of sympatry. The characteristics most interesting for species differentiation were the linear distribution pattern of the mounds and the occurrence of ‘earth sausages’ and ‘earth paths’, all of them typical of moles. The high correlation coefficients (r _s ?>?0.88) obtained between animal captures and the presence of activity signs for the two vole species revealed that it is possible to estimate A. t. cantabriae and M. lusitanicus densities by using the presence signs. An estimating model adapted for apple orchards and for simultaneous sampling both voles is proposed. In addition, we confirmed that the three mammal species coexist frequently in the same orchards. The negative relation between A. t. cantabriae and M. lusitanicus numbers suggests a competitive displacement between species. The results of the present study have valuable applications for both crop protection and research purposes.