Amount of corticosterone metabolites in the fecal samples of common vole mothers ( Microtus arvalis ). Mothers were either treated with a nest predator (NP, shrew, Crocidura russula), an interspecific resource competitor (RC, field vole, M. agrestis) or an intraspecific competitor control individual (C). Samples were taken at three reproductive phases (sampling b, I, II) within one reproduction cycle of each female common vole. b: baseline; taken after 3 days of habituation to enclosures (at day 15 of common voles’ pregnancy) before treatment. I: Sample taken around parturition and 3 days after adding treatment animals to enclosures (at day 18 of pregnancy). II: Sample taken with having 5 days old nestlings.