Active vision during prey capture in wild marmoset monkeys.

A foundational pressure in the evolution of all animals is the ability to travel through the world, inherently coupling the sensory and motor systems. While this relationship has been explored in several species, it has been largely overlooked in primates, which have typically relied on paradigms in which head-restrained subjects view stimuli on screens. Natural visual behaviors, by contrast, are typified by locomotion through the environment guided by active sensing as animals explore and interact with the world, a relationship well illustrated by prey capture. Here, we characterized prey capture in wild marmoset monkeys as they negotiated their dynamic, arboreal habitat to illustrate the inherent role of vision as an active process in natural nonhuman primate behavior. Not only do marmosets share the core properties of vision that typify the primate Order, but they are prolific hunters that prey on a diverse set of prey animals. Marmosets pursued prey using vision in several different contexts, but executed precise visually guided motor control that predominantly involved grasping with hands for successful capture of prey. Applying markerless tracking for the first time in wild primates yielded novel findings that precisely quantified how marmosets track insects prior to initiating an attack and the rapid visually guided corrections of the hands during capture. These findings offer the first detailed insight into the active nature of vision to guide multiple facets of a natural goal-directed behavior in wild primates and can inform future laboratory studies of natural primate visual behaviors and the supporting neural processes.