Numerical response of mammalian carnivores to rodents affects bird reproduction in temperate forests: a case of apparent competition?

Resource pulses such as mast seeding in temperate forests may affect interspecific interactions over multiple trophic levels and link different seed and non-seed consumers directly via predation or indirectly via shared predators. However, the nature and strength of interactions among species remain unknown for most resource pulse driven ecosystems. We considered five hypotheses concerning the influence of resource pulses on the interactions between rodents, predators and bird reproduction with data from northern Switzerland collected between 2010 and 2015. In high-rodent-abundance-years, wood warbler (Phylloscopus sibilatrix) nest survival was lower than in low-rodent-abundance-years, but rodents were not important nest predators, in contrast to rodent-hunting predators. The higher proportion of nests predated by rodent-hunting predators and their increased occurrence in high-rodent-abundance-years suggests a rodent-mediated aggregative numerical response of rodent-hunting predators, w...