Food dropping as a food transfer mechanism among western lowland gorillas in Moukalaba-Doudou National Park, Gabon

摘要

In this paper, I describe the food-dropping behavior of western lowland gorillas observed in Mouka-laba-Doudou National Park, Gabon. I collected observational data of gorillas eating in trees, and recorded whether any individuals were positioned under the same tree. In 22 of the 24 cases of individuals being present under a tree, I observed the gorilla in a tree dropping food to the individual below. In most cases, the recipient was a silverback or an elder half-sibling of the dropper. The dropper'selder full-sibling was never a recipient. The food-dropping behavior of Moukalaba western lowland gorillas is likely due to a combination of factors: their frugivory, arboreal-ity, large body size, and the scarcity of terrestrial herbs. It is difficultfor multiple gorillas to simultaneously feed in the same tree. Under such limitations, younger gorillas face difficulties in defending their feeding patches from older individuals. Nearly 90 % of the recipients were older than the food droppers. Furthermore, food droppers were significantly younger than non-food droppers who simultaneously fed on the same tree, and most-food recipients were significantly older than least-food recipients on the ground. Food dropping may, therefore, be a tactic employedby younger gorillas to defend a feeding site from older individuals. This study suggests that food dropping may reduce feeding contest competition in a gorilla group in Moukalaba. This is a preliminary study that indicatesthat food dropping may be intentionally used as a way to reduce feeding competition; nevertheless, further studies are needed.