Small Mass of Rattus norvegicus ( Rodentia: Muridae) on the Ogasawara Islands, Japan

Norway rats (Rattus norvegicus) on the Ogasawara Islands exhibit extraordinarily small body mass, approximately half that of rats in other regions like Hokkaido, Yokohama, and Tokyo Bay. This study attributes the reduced size to environmental factors rather than genetic differences, as morphological traits such as crown length, head-body length, and tail length remained consistent across populations. Stomach content analysis revealed a predominantly plant-based diet (95.2% by volume), deviating from the species' typical preference for protein-rich foods, suggesting that dietary limitations may restrict body mass growth in these rats.

Yabe, T., Horikoshi, K., & Hashimoto, T. (2017). Small Mass of Rattus norvegicus ( Rodentia: Muridae) on the Ogasawara Islands, Japan. Pacific Science, 71(3), 257–268. https://doi.org/10.2984/71.3.2