2020 Volume 60 Issue 2 Pages 171-179
Japanese walnut (Juglans mandshurica) is commonly infested by the larvae of the Indian meal moth (Plodia interpunctella). Japanese squirrels (Sciurus lis) that mainly feed on walnuts could increase their foraging efficiency if they could discern healthy or insect-damaged walnuts before they crush to feed on or transport them. In this study, we experimentally examined how Japanese squirrels and sympatric raccoon dogs (Nyctereutes procyonoides) deal with two types of walnuts (infested or healthy), in Okutama, Tokyo. We found that squirrels selected healthy nuts at a significantly higher rate at the beginning of contact and abandoned insect-damaged nuts quicker than raccoon dogs. The behavioral patterns of squirrels were significantly different according to the type of walnut they started to touch, while those of raccoon dogs did not differ regardless of the type. It is likely that squirrels can change their behavior according to the type of the walnut before and during picking up the nut, unlike raccoon dogs, thereby reducing the risk of feeding on, transporting, and storing insect-damaged nuts found on the forest floor. In comparison, raccoon dogs do not discriminate between a healthy nut and an insect-damaged nut.
