Search for: [Description = "The density of the field mouse Apodemus agrarius \(Pallas, 1771\) was estimated twice during the course of a year, using the Petersen index, in one of the green spaces of Warsaw. The densities obtained, 88 and 39 individuals\/ha, are higher than those given for areas outside towns. The biotic and abiotic factors responsible for such high densities are discussed."]