Western Gorilla - Behavior and Ecology

Behavior and Ecology

Western gorillas live in groups that vary in size between two and 20 individuals, composed of at least one male, several females and their offspring. A dominant male silverback heads the group, with younger males usually leaving the group when they reach maturity. Females transfer to another group before breeding, which begins at eight to 9 years old; they care for their young infant for the first three to four years of its life. The interval between births, therefore, is long, which partly explains the slow population growth rates that make the western gorilla so vulnerable to poaching. Due to the long gestation time, long period of parental care, and infant mortality, a female gorilla will only give birth to an offspring that survives to maturity every six to eight years. Gorillas are long-lived and may survive for as long as 40 years in the wild. A group's home range may be as large as 30 square km, but is not actively defended. Wild western gorillas are known to use tools.

Western gorillas' diets are high in fiber, including leaves, stems, fruit, piths, flowers, bark, invertebrates, and soil. The frequency of when each of these are consumed depends on the particular gorilla group and the season. Furthermore, different groups of gorillas eat differing numbers and species of plants and invertebrates, suggesting they have a food culture. Fruit comprises most of the gorillas' diets when it is abundant, directly influencing their foraging and ranging patterns. Fruits of the generas Tetrapleura, Chrysophyllum, Dialium, and Landolphia are favored by the gorillas. Low-quality herbs, such as leaves and woody vegetation, are only eaten when fruit is scarce. In the dry season from January to March, when fleshy fruits are few and far between, more fibrous vegetation such as the leaves and bark of the low-quality herbs Palisota and Aframomum are consumed. Of the invertebrates consumed by the gorillas, termites and ants make up the majority. Caterpillars, grubs, and larvae are also consumed in rarity.

Some ethnographic and pharmacological studies have suggested a possible medicinal value in particular foods consumed by the western gorilla. The fruit and seeds of multiple Cola species are consumed. Given the low protein content, the main reason for their consumption may be the stimulating effect of the caffeine in them. Western gorillas inhabiting Gabon have been observed consuming the fruit, stems, and roots of Tabernanthe iboga, which, due to the compound ibogaine in it that acts on the central nervous system, produces hallucinogenic effects. It also has effects comparable to caffeine. There is also evidence for medicinal value for the seed pods of Aframomum melegueta in lowland gorillas' diets, which seem to have some sort of cardiovascular health benefit for lowland gorillas, and are a known part of the natural diets for many wild populations.

A study published in 2007 in the American Journal of Primatology announced the discovery of this species fighting back against possible threats from humans. They "found several instances of gorillas throwing sticks and clumps of grass." This is unusual, because gorillas usually flee and rarely charge when they encounter humans.