Quercus acorns and coniferous cones are the main food sources for tree squirrels, and the chemical contents of seeds, such as tannins and terpenes, are predicted to affect the squirrels' food preference. The tolerance of squirrels to chemical contents may vary between species that have evolved in different environments. The consumption of artificial food containing tannic acids or terpenes were compared between the endemic Sciurus lis and two alien species, S. vulgaris and Callosciurus erythraeus. Sciurus lis ate foods containing up to 4% tannic acid, whereas S. vulgaris and C. erythraeus ate foods containing 8% tannic acid. Sciurus lis and S. vulgaris could eat food containing a high concentration of terpenes (up to 0.3% α-pinene and 2% limonene), whereas the food consumption by C. erythraeus decreased drastically with increasing terpene concentrations. The two alien squirrels are highly resistant to tannins and thus the acorns of most Quercus species may be available for them. Sciurus lis exhibits a lower tolerance to tannins, but can consume foods with high concentrations of terpenes, suggesting a strong adaptation to coniferous forests, but not to Quercus forests. More attention must be paid to conserving suitable habitats for S. lis, an endemic relict species.