Walnut Hoarding by the Japanese Wood Mouse, Apodemus speciosus Temminck

Abstract

Walnuts, Juglans ailantifolia Carriere, are large and the shell is difficult to open. Thus, seed predators in Japan are restricted mainly to the Japanese squirrel (Sciurus lis Temminck) and the wood mouse (Apodemus speciosus Temminck), which can shave away the hard shells with their sharp incisors. Previous work indicated that the squirrels are not only predators, but also disperse walnuts. In this study, 95 walnuts in Period1 (September 1996–February 1997) and 80 walnuts in Period 2 (September 1999–February 2000) each attached to a miniature radio transmitter, were placed in a feeding box, and 93 and 53 of them were transported by free-living wood mice in the respective periods. Most of the walnuts provided from September to November were scatter-hoarded in the litter layer, while from December to February, the mice fed immediately and seldom scatter-hoarded on the ground surface. In all, 66 walnuts were hoarded and 80 were eaten soon after discovery, although walnuts were eaten more frequently in Period 1 than in Period 2, which may be related to annual differences in seed crop size in the study site. The mean transport distance of hoarded seeds was 6.2 ± 5.0 m (mean ± SD, n=66). The fate of hoarded walnuts was followed from September 1996 to May 1997; 21 (75%) of the scatter-hoarded walnuts were recovered, but 7 (25%) were left uneaten. Consequently, the Japanese wood mouse also plays a role in seed-dispersion of the walnut, but the transport distance for mice was shorter than that for squirrels.

Key words:

• Apodemus speciosus
• hoarding
• Juglans ailantifolia
• seed-dispersion