Insect‐eating by sympatric Lowland gorillas (Gorilla g. gorilla) and chimpanzees (Pan t. troglodytes) in the Lopé Reserve, Gabon

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Abstract
Sympatric populations of lowland gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes troglodytes) in the Lopé Reserve in central Gabon consumed insects at similar average frequencies over a 7-year period (30% versus 31% feces contained insect remains). Data came mostly from fecal analysis supplemented by observation and trail evidence. The weaver ant (Oecophylla longinoda) was the species eaten most frequently by both gorillas and chimpanzees. Other species of insects wore eaten but there was virtually no overlap: Chimpanzees used tools to eat Apis bees (and their honey) and two large species of ants; gorillas ate three species of small ants. Thus, despite their shared habitat, the esources utilized were not identical as gorillas do not show the tool-use “technology” of chimpanzees. The frequency of insect-eating by both species of ape varied seasonally and between years but in different ways. This variation did not seem to be related to the ratio of fruit to foliage in their diets. Gorillas of all age-classes ate insects at similar rates. Comparisons with insectivory by other populations of gorillas indicate differences exist. Mountain gorillas (Gorilla g. beringei) in the Virunga Volcanoes, Rwanda, consume thousands of invertebrates daily, eating them inadvertently with handfuls of herbaceous foods but they deliberately ingest insect-foods only rarely. Lowland gorillas at Lopé habitually ate social insects, and their selective processing of herbaceous foods probably minimizes inadvertent consumption of other invertebrates. Gorillas at Belinga in northeastern Gabon, 250 km from Lop6, ate social insects at similar rates but ignored weaver ants in favor of Cubitermes sulcifrons, a small species of termite that occurs at Lopé but was not eaten by gorillas. This indicates that local traditions similar to those reported for chimpanzees also exist amongst populations of gorillas.

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