Nikkor 200-500 VR/TC 14 III @550mm, f8, high ISO (4000); Nikon D750
Black-mantled tamarin; apart from insect and fruit, always looking for sap of a favourite tree.
It seemed to be breaking off pieces of bark using hands (they can’t use their teeth like marmoset) working on the existing holes (Saguinus nigricollis; it may look like it but not graellsi, whether sp. or ssp. - on the Peruvian border)