Characteristics of gouging by captive-born silvery marmosets in gum-producing trees.

Marmosets are obligate gummivores with evolutionary adaptations to harvesting tree exudates. We studied a group of zoo-living free-ranging silvery marmosets (Mico argentatus) that had learned to feed from Prunus spp., to investigate the characteristics of the holes they gouged in four Portuguese laurel trees (Prunus lusitanica). Holes were frequently extended in more than one direction from the base, often producing roughly V-shaped channels. The angles of the holes from the vertical were significantly different from a random distribution and averaged 40° ± 2.1 SE. Mean hole length was 50.9 mm ± 3.4 SE. Mean depth of gouge holes was 5.08 mm ± 0.17 SE and was consistent along the length of the holes. Feeding on Prunus was concentrated in the late morning, and constituted 26.2% of records of the marmosets' overall activity during group scans. Further studies are needed to investigate whether there are consistent species or generic differences in the methods used to harvest gum by marmosets, and whether marmosets use different gouging techniques for different plant species. Understanding how marmosets identify and use new gum sources will be important for their conservation in habitats altered by anthropogenic impacts.