In terms of sheer quantitative abundance, rodents are by far the most dominant prey group in the diet of the Eurasian eagle-owl. Roughly 130 species of rodent are known to have been taken by these owls. Due to their small sizes, however, rodent prey often comprise a relatively small portion of the prey biomass, excepting relatively large rodents such as mice, rats and hamsters, some of which weigh at least . In many parts of Europe, the most numerous prey in dietary studies are the brown rat and the common vole, followed by the nearly as widespread field vole (Microtus agrestis). Among the areas where the common vole was the leading prey species included southern Sweden, Germany, Poland, the Czech Republic, and Slovakia. In areas that have undergone more heavy development, the brown rat predominates, being the leading prey item in several parts of France including Côte-d'Or, Lozère and even the remote Pyrenees, Belgium, the Italian Alps, and Brașov, Romania. The brown rat is even the primary prey in Lebanon despite it being tied solely to human habitations as the environment is often too arid to allow it to survive further afield. Black rats (Rattus rattus), at , are also hunted but rarely in equal number to the generally more successful brown rats. In Norway and Finland, field voles were the most numerous prey species, per one study in the latter country it made up 30.1% of the food but only provided 3.3% of the prey biomass. The European water vole, averaging at , was the main prey species in Styria, Austria, although considerably secondary in biomass to hedgehogs, as well as in central Sweden. The water vole often the second or third most regularly found prey species in several other European studies. In Samara, Russia, the diet is dominated by the European water vole, although other species such as European hamsters (Cricetus cricetus) and European hares (Lepus europaeus) (both also significant prey there) probably outweigh them in biomass contribution. The common vole and European water vole together made up roughly 80% of the prey by number in the High Tatras of Slovakia and more than 60% of the diet in bordering Poland.