Just looking at some journals, and i didn't realise barn owls were so widespread (every continent except antarctica). I read a few things on natural foods, and it seems it is completely varied in where they come from. For example, in south madagascar they hunt 95% rodents, with the occasional small lizards and amphibians found in their pellets. However, in parts of tunisia the diet consists largely of rodents and the three-toed Jerboa (Jaculus jaculus) that accounted for more than 50% of total prey biomass. In these open habitats with xerophytic vegetation, the Barn Owl hunts almost only small mammals, mainly jerboas and gerbils, and very occasionally insects, amphibians, reptiles and birds.
In Baja California a study of barn owl pellets gave results of 282 rodent skulls, 74.4% were of Heteromyidae family 11.3% of Muridae, and 14.3% of Geomyidae. Plant and insect remains (55.5% and 9.2%, respectively) were also present. Sub-adult rodents were present in 61.9% of the pellets, and rural rodents composed 83.3% of the prey.
However i have noticed that all results from different papers suggest that barn owls show a nonrandom tendency toward rodent species especially small
and young individuals.