12.41% by number (but only 5.73% by biomass) and water voles at 22.24% by biomass (but only 10.1% by number). In the same study area during a poor vole year, amongst 860 prey items, voles trailed other prey such as birds and shrews by number, but water voles were taken more or less in the same numbers here as in the peak vole years. Another study estimated the mean weight of Finnish Ural owl prey as . Similar dietary habits were found for Ural owls in Sweden, in 2309 prey items, water voles made up 33.1% of prey by number and 60% of the biomass, field voles composed 30.8% by number and 14.5% of the biomass and bank voles made up 11.8% of the prey by number and 3.3% of the biomass.Lundberg, A. (1981). Population ecology of the Ural owl Strix uralensis in central Sweden. Ornis Scandinavica, 111-119. Camera traps recording captured 187 prey items for Ural owls in 5 nests in Värmland County, Sweden found that voles were secondary in delivery rates to common shrew (Sorex araneus) and various birds with the small size of such prey requiring frequent deliveries although this was offset with fair numbers of young hares apparently available to these owls. As the Ural owl ranges south, prey populations tend to become slightly less cyclical but also apparent access to large prey such as water vole appears to be reduced.Lõhmus, A. (1999, January). Vole-induced regular fluctuations in the Estonian owl populations. In Annales Zoologici Fennici (pp. 167-178). Finnish Zoological and Botanical Publishing Board. In the relatively northerly Latvia, of 2615 prey items, voles constituted just over half the diet and the prey base was relatively diverse. For Latvian owls, the main prey species were bank vole (at 18.09% by number, 9.2% by biomass), field vole (17.13% by number, 13.85% by biomass) thence European mole (Talpa europaea) (9.83% by number, 12.3% biomass), the latter at a mature mass of about ). In Belarus, Microtus species were quite regular prey in vole peak years, at 45% by number and 29.9% biomass, against crash years when they were merely 6.7% by number and 4% by biomass while the less cyclical bank voles were 29% by number and 20.4% in biomass in peak years and 38.1% by number, 23.8% by biomass in crash years. Furthermore in Belarus, shrews and moles went from 6.4% to 14.3% by number during the