Birds of prey exert pressure on root vole populations in winter and spring

Background Small rodents and their intricate population dynamics have long been a focus of research interest, but despite birds being one of the main predators of rodents, the impact of avian predation on rodent populations remains poorly studied. To fill this gap, we conducted a field experiment in a temperate grassland, in which we excluded bird predation in populations of the root vole ( Microtus oeconomus ) throughout the year. Methods We covered open plots in three locations with netting and used capture-mark-recapture method to estimate the effect of this treatment on vole survival and population size, accounting for body mass and sex of individuals. Results We found that avian predation exclusion increased vole survival in winter and spring (November to May). Survival of voles with bird predation was up to 22% lower compared to plots with no bird access. Large voles faced the highest mortality during this period, and avian predation did not affect this pattern. Conclusions This research contributes to our understanding of the causes of winter vole population collapses by demonstrating that bird predation has the greatest impact on vole survival and abundance during the winter-spring period, even in the presence of persistent snow cover.