It has been determined that timescales of the beginning of summer intensive epizootics in the plain natural plague foci of souslik type in the Northern, North-Western Pre-Caspian and Pre-Caucasus Regions coincide with the period of adult small sousliks migration to the landscape lowering, building of protective burrows, and formation of flea micro-populations in them. Substantiated is existence of the mechanism that determines seasonal character of animals infecting during 30–40 days (III decade of May – II decade of June) at the same sites of focal territory.