The common vole (Microtus: Rodentia) age groups selectivity in long-eared owl’s (Asio otus: Strigiformes) diet

Presence of different age groups of prey-species in the long-eared owl diet (Asio otus L., 1758) has been analyzed. Age groups have been determined by the relative measurements which have been estimated by a mandible length. All samples of Microtus spp. mandibles are forming distribution curves, which are close to normal by its statistical parameters. Furthermore, the winter samples are characterized by a positive excess (Ex from 0.0 to 1.9), and summer ones – by a negative excess (Ex -0.9), what is according to nature state of voles populations. It has been cleared that owl’s diet selectivity shows a character of accidental elimination which is connected with stabilizing selection effect. It has been determined, that changes of an age structure of prey population under influence of owl predation carry nondirectional fluctuating character. The importance of owl’s diet selectivity for interpretation of paleontological material, represented by small mammals, is considered.