BITE FORCES USED BY JAPANESE MACAQUES (MACACA-FUSCATA YAKUI) ON YAKUSHIMA ISLAND, JAPAN TO OPEN APHID-INDUCED GALLS ON DISTYLIUM-RACEMOSUM (HAMAMELIDACEAE)

Japanese macaques on Yakushima Island have been seen attempting to ope n thick, woody plant galls in order to eat aphids contained within the m. We analysed a sample of galls and gall fragments with toothmarks an d found that 22% were still intact indicating a failure to open them. These marks were examined and measured. Teg pits had a mean indentatio nal area of 1.44mm(2) (S.D. 0.28mm(2)), while 15 elongated scratches h ad a mean width of 1.26mm (S.D. 0.27 mm). The gall resembled a lightwo od in its mechanical properties and had a microhardness of 80.4 MPa. A ssuming that at least two marks were formed in any given bite, indenta tional analysis gave a mean estimate of bite forces of 232 N (maximum 291N) to produce pits and 255N (maximum 487N) to produce scratches. Th ese forces are consistent with, but at the high end of, limits predict ed by anatomical analysis.