A friend in need is a friend indeed: feeding association between Japanese macaques and sika deer

“Gleaning” is a behaviour observed in feeding associations between arboreal and ground-dwelling animals, wherein the former drop plant items that the latter consume. However, it is not well known whether gleaning is in fact beneficial for the ground-dwelling animals. We observed the gleaning association between sika deer,Cervus nippon Temminck, 1838, and Japanese macaques,Macaca fuscata Blyth, 1875, for 6 years (May 2000 to December 2005) on Kinkazan Island, northern Japan. The gleaning occurred most frequently in spring (from March to May, 28 events), followed by fall (from September to November, 15 events). Gleaning frequency seemed to be affected by both food shortage and nutritional requirement of the deer. Nutritional values of “gleaning foods” dropped by the macaques were higher than those of other non-gleaning foods. These results suggest that the gleaning association with macaques is beneficial to the deer.