Selective herbivory in tassel-eared squirrels: role of monoterpenes in ponderosa pines chosen as feeding trees.

Ponderosa pine twigs collected from trees used by tassel-eared squirrels as sources of cortical tissue for food contained smaller amounts of monoterpenes than twigs from similar trees not used by the squirrels as food sources. Of the 18 monoterpenes isolated from the twig samples, alpha-pinene was the best single predictor of food source trees. In experiments with captive tassel-eared squirrels, consumption of a preferred food was inversely correlated with the concentration of alpha-pinene added to the food.