Patterns of predator behaviour and wood warbler Phylloscopus sibilatrix nest survival in a primaeval forest

Understanding the foraging behaviour of predators is key to interpreting the role of anti-predator adaptations of birds in reducing nest losses. Conducting research in primeval habitats, with low direct human interference, is particularly valuable in the understanding of predator-prey interactions. Using nest cameras, we investigated the identity and behaviour of potential and actual predators appearing at Wood Warbler Phylloscopus sibilatrix nests, and the importance of different predator groups for nest survival, in the primeval part of Białowieża Forest (Poland). Mammals formed the main predator group (30 of 32 nest depredations), particularly medium-sized carnivores (24 of 32), which attacked nests more frequently than merely passing by. This contrasted with other species, especially small rodents that were commonly recorded near nests but rarely attacked them. Most nest attacks (22 of 32) took place at night and nest survival did not depend on nest visibility, indicating a reduced utility of nest concealment in defence against predators using mainly sound or olfaction when hunting. Daily nest survival declined strongly with nest progression (from egg-laying to fledging of chicks), likely due to increased predator detection of nests containing older and louder chicks, and not due to increasing parental activity at nests during the day. The set of actual nest predators differed from some previous studies in human-transformed habitats, showing that Wood Warblers may face differing threats in modified versus near-pristine environments.