Avian predation has the strongest impact on vole survival during winter and spring in temperate grasslands

Predation is widely acknowledged as an important factor affecting small rodent populations, yet its specific impact on their dynamics is not fully understood. In seasonal environments, winter and early spring are critical periods for small mammal populations, as environmental stressors – including predation – coincide with an inability to offset mortality through reproduction. Although birds of prey are major rodent predators, their effect on prey populations during this period remains poorly quantified. To address this, we conducted a year-round field experiment in temperate grasslands, excluding avian predators from root vole ( Microtus oeconomus ) populations using net-covered plots in three locations. Vole survival and population size were assessed using capture–mark–recapture method, considering effects of sex and body mass of individuals.Our results show that avian predation significantly reduced vole survival during winter and spring (November–May), increasing mortality by up to 22%, even when under snow cover. In contrast, no effect was detected during the rest of the year, and bird predation did not influence seasonal population dynamics. Overwinter survival was negatively associated with body mass, with larger individuals experiencing higher mortality; this pattern was not modified by predation exclusion.These findings demonstrate that avian predators exert substantial seasonal pressure on vole survival, contributing to winter–spring population declines. However, the influence of bird predation appears limited in shaping long-term population dynamics.