Tamura, Noriko (2011). "Population Differences and Learning Effects in Walnut Feeding Technique by the Japanese Squirrel". Journal of Ethology. 29 (2): 351–363. doi:10.1007/s10164-011-0267-z.
Tamura, N.; Hayashi, F. (2008). "Geographic variation in walnut seed size correlates with hoarding behaviour of two rodent species". Ecol. Res. 23 (3): 607–614. Bibcode:2008EcoR...23..607T. doi:10.1007/s11284-007-0414-8.