One of Cayo Santiago’s rhesus superstars, Pinocchio or 84J, made it to BBC News after Comins et al wrote a short article for the Journal of Ethology. The article recorded this particular macaque’s “innovative and highly beneficial foraging behavior.” They reported that this male rhesus has been able to open the coconut by tossing it on a cement dock or at any hard surface on the island until the hard shell cracks and the white flesh is exposed.
The researchers explained the mechanics of Pinocchio’s nut-cracking technique:
The coconut-opening behavior of 84 J has two notable components: a horizontal toss and an underhand vertical throw. The horizontal toss is used to transport the coconut as he moves towards the island’s dock. This is a useful technique since it is cumbersome for a largely quadrupedal rhesus to carry a coconut in one or both arms. The second component of the coconut-opening behavior occurs once 84 J has reached the rocky area near the island’s dock. Rearing back on his hind legs, he springs upward into a small hop while concurrently propelling his front arms upward in an underhand throw. Towards the peak trajectory of his hop and throw, 84 J releases the coconut from his front hands, projecting the coconut upwards and then allowing it to fall on the nearby cement or rocky terrain. This process is repeated until the shell cracks, allowing him access to the flesh inside.
Despite the efficiency of 84J’s nut-cracking abilities, this innovation has not been transmitted to the Cayo Santiago macaques or to Pinocchio’s immediate group. Although Comins et al suggest a “systematic investigation” to understand this foraging behavior and its social learning implications, I would like to add my two cents anyway regarding the potential factors that may have prevented the transmission of the nut-cracking skills from 84J to the rest of the troop:
Firstly, coconuts are high-energy expenditure food items requiring more effort on the part of the macaque forager (climbing, unhusking, throwing, breaking). Coconuts are said to be “plentiful” on the island, but may in fact be minimal if compared to the relative abundance of other low-energy expenditure food sources (e.g., monkey chow, leaves, clay, and mangrove saplings). The presence of these food items could be a factor in lessening the incentive for seeking out coconut as a food resource.
Besides in a small island like Cayo with a macaque population of around 1000, the number of actual coconut trees may not be enough to encourage coconut foraging unless, of course, if there is a food preference for coconuts over other food items. In this regard, given the relative scarcity of coconuts on the island, it would thus be interesting to investigate the frequency of 84J’s nut-cracking activities (ditto with the mention in the article of Berard’s account of two macaques opening a coconut in full view of conspecifics).
Secondly, one way to address the conundrum is to determine the position of 84J in the Cayo macaque social organization and his behavioral tendencies. For example, low-ranking males usually stay at the periphery with minimal interaction with most of the individuals while high-ranking males stay more (and get to interact more) with individuals in the group . Thus, the position of 84J in the dominance hierarchy (and the nature of male migration) may also have been factors in the non-transmission of this innovative behavior. An investigation into Pinocchio’s social behavior would also reveal the range of possibilities for transmission.
These blog ideas are mere shots from the hip. Comins et al’s recommendation for a systematic investigation into 84J’s behavior should thus be heeded in order to understand more thoroughly the nature of primate social learning and cognition.
Jordan A. Comins • Brian E. Russ •, & Kelley A. Humbert • Marc D. Hauser (2010). Innovative coconut-opening in a semi free-ranging rhesus monkey
(Macaca mulatta): a case report on behavioral propensities
Vodpod videos no longer available.