Background information and definitions
Many primate species are leaf eaters which spend significant amounts of time browsing in the wild. In captivity, pellet and produce-based diets are supplemented with cut branches from trees and shrubs referred to as browse. Browse is an important dietary component but also aims to increase time spent feeding and promote natural foraging behaviours.
Supporting evidence from individual studies
A replicated, before-and-after study in 2006 at three zoos in the Netherlands and Germany (Tennie et al. 2008) found that western lowland gorillas Gorilla gorilla gorilla, presented with stinging nettles Urtica dioica, used the same processing skills as wild mountain gorillas, Gorilla beringei beringei. Eight of nine captive western lowland gorillas gathered and processed leaves before eating them (just as wild mountain gorillas do). A captive gorilla with no experience of nettles gathered and processed leaves 32% of the time and omitted the process stage 59% of the time. As a comparison, captive gorillas given willow plant Salix sp., omitted the process stage 79% of the time and 17% of the time ate the leaves as soon as the willow was obtained. Leaves were offered either inside or as a scatter feed outside. Sixty-eight hours of video contained 296 behavioural sequences of nettle feeding from nine gorillas and 176 behavioural sequences of willow feeding from 11 gorillas. (CJ)Study and other actions tested