Nest-box supplementation for Eurasian kestrel and barn owl as a biological control tool for common vole (Microtus arvalis) outbreaks in croplands in NW Spain

Resumen del trabajo presentado a la 10th European Vertebrate Pest Management Conference, celebrada en Sevilla (España) del 21 al 25 de septiembre de 2015.Biological control of rodents based on the management of raptor populations could aid to prevent or reduce agricultural damage by rodents, and therefore minimize the use of rodenticides. Recurrent common vole population outbreaks have been occurring in NW Spain during the last 40 years. These outbreaks have led to large-scale application of anticoagulant rodenticides. Since 2009, looking for a potential alternative to rodenticides, we installed a total of 300 nest-boxes over poles in three experimental areas of 2000 ha. Three nearby areas of similar extension and habitat were considered as control areas. Vole abundances were monitored three times yearly (late winter, summer and autumn) as well as the abundance of raptors, which was monitored by conducting kilometer index of abundance (KIA). The use of nest-boxes and breeding parameters for kestrels and barn owls were also recorded yearly. During the study period, a large-scale vole outbreak occurred in 2013-2014 and a lesser population peak occurred during 2011. In the treatment areas, the supplementation of nest-boxes significantly increased the abundance of kestrels, especially during summer, and also increased buzzard abundance during winter. Vole abundance was lower or more stable in the experimental areas as compared with control areas during 2011, but differences were not detectable during the 2014 outbreak in two study areas. Overall, biological control by raptors may help to control vole densities in agricultural land but may require aditional actions on large-scale vole outbreak years (increasing nest-box density, the size of the treatment area or using complementary environmentally friendly techniques).Peer Reviewe