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Jean-Baptiste Leca, Ph.D.

Associate Professor

Department of Psychology

University of Lethbridge


A new case of fish-eating in Japanese macaques: Implications for social constraints on the diffusion of feeding innovation

We investigated how socio-ecological features may constrain the long-term maintenance of a particular feeding innovation in a free-ranging social group of Japanese macaques under natural conditions.

We documented a seldom observed event of fish-eating, involving a new fish food species for the monkeys on Koshima island.


Following the discovery of a large beached sea bass by a peripheral male, we observed a total of 16 individuals feeding on the fish in turns, and interacting around it.

The rank order of access to the fish was mainly explained by the spatial position of group members, whereas dominance determined how long the fish was monopolized.

Although limited, the tolerated presence of close-bystanders while feeding was affected by kinship and affiliation.

We examined the complex ecological and social conditions under which feeding innovation and its subsequent propagation may occur in natural populations of Japanese macaques.

We also assessed the long-term diffusion and maintenance of the fish-eating habit in Koshima monkeys by updating an existing genealogy of lineages of fish eaters recorded on the island.

Genealogical data suggested that fish-eating behavior was well maintained in terms of maternal lineages.

This study contributed to a better understanding of the various factors facilitating and those limiting the appearance and maintenance of feeding innovations in wild primate groups.