Coexistence of roof rats and carnivores in barns on a livestock farm in Japan

Brown rats (Rattus norvegicus), roof rats (Rattus rattus), and house mice (Mus musculus) are considered to be important pests on livestock farms. Although the diel activity patterns of rodents are key to their control, information on this aspect of their ecology is limited. Furthermore, the effect of carnivores on rodent activity patterns as well as the carnivore species present on livestock farms is unclear. Here, we set camera traps in an open-type cow barn and in an enclosed pig barn on the same livestock farm in Japan from August through October 2021. The only rodents observed in both barns were roof rats, and the carnivore species observed were dogs (Canis familiaris), cats (Felis catus), and Japanese weasels (Mustela itatsi). Roof rats showed different patterns of activity and behavior between the barns. However, because the pattern in both barns was nocturnal, the activity patterns of roof rats and carnivores showed a moderate to high degree of overlap. Therefore, roof rats did not appear to shift their activity patterns to avoid nocturnal carnivores. Taken together, the present study provides valuable information for rodent control on livestock farms in Japan.