Objectives: Wild Sapajus libidinosus exploit underground storage organs (USOs) that
require extraction and extensive processing before consumption. Since capuchin
monkeys are small-sized extractive foragers that cannot perform forceful precision
grips, we expected that: (a) they would use other body parts together with their
hands, (b) older (and larger) capuchins would be more efficient than younger (and
smaller) ones, and (c) capuchins would invest greater effort/time to exploit USOs
than other foods.
Materials and Methods: We recorded 178 episodes of USO processing performed
by 20 individuals. The behavior was videotaped and scored frame-by-frame.
Results: We identified six sequential stages of processing: Excavation, extraction, soil
removal, transport, peeling, and fragmenting the inner tissues. Capuchins made frequent
use of forceful hand postures and manipulation in which the hands were
strongly supported by other body parts, principally the mouth. Older capuchins were
more efficient than younger individuals in pulling the USOs out of the ground. Finally,
exploiting USOs was time-consuming, lasting more than 4 min per item, on average.
Discussion: Despite having smaller body-mass and greater manual constraints than
catarrhine extractive foragers, capuchins, even smaller individuals, mastered USO
processing thanks to their behavioral flexibility and persistence. Our findings reveal
that precision grips are not essential for forceful actions during complex food
processing and that, unlike catarrhines, capuchins, especially adults, rarely use thumb
opposition during forceful grasping of food. In contrast, extended sustained attention
and varied manual behavior appear to be convergent features of platyrrhine and catarrhine
extractive foragers.
