Mountain Gorilla Seasonal Diet — Following the Food Calendar
Mountain gorillas are generalist herbivores whose diet is shaped by the seasonal availability of the Virunga and Bwindi montane forest food base — a food base that varies significantly across the year in both composition and abundance, producing changes in gorilla ranging behaviour and daily activity patterns that are directly observable during the gorilla trekking encounter if the visitor knows what to look for. The gorillas are, at their most fundamental level, animals whose entire daily schedule is organised around food availability, and the seasonal variation in that availability produces the variation in where they are, what they are doing, and how far they travel that makes each gorilla trek slightly different from every other.
The Bamboo Shoot Season
At Volcanoes National Park, the February-to-April rainy season produces the bamboo shoot flush — the period when new bamboo shoots push through the soil across the bamboo belt at the park’s lower elevations (2,400–2,600 metres), providing a food resource that is highly preferred by mountain gorillas relative to their baseline diet of leaves and stems. During the bamboo season, all habituated families in Rwanda shift their daily ranging toward the lower elevation bamboo belt and can be found spending the majority of their active time feeding on shoots that are harvested by grasping the shoot base and pulling upward to snap the shoot at its natural break point.
The bamboo season has a practical implication for gorilla trekking visitors: during the months when families are concentrated in the lower bamboo belt, approach walks are shorter and the terrain is less steep than when families range at higher montane altitudes. The bamboo season represents both a food event for the gorillas — a period of higher-quality, more abundant feeding than the baseline herbaceous diet provides — and a coincidentally more accessible approach for trekkers.
Dry Season Ranging — Higher Altitude, More Fruit
During the June–September and December–January dry season periods at Volcanoes National Park, fruit-bearing species at higher altitudes — particularly Pygeum africanum (African cherry) and various Rubus species — produce the ripe fruit that mountain gorillas seek. Fruit is not a staple food for mountain gorillas (whose digestive system and tooth morphology are adapted for the high-cellulose diet of leaves and stems), but it is a highly preferred food when available, and the families’ ranging tracks follow the fruiting phenology of the higher-altitude species during the dry season. This produces the longest approach walks and the most elevation gain for trekking visitors, because the families are at higher altitude, but it also produces the largest individual fruit-bearing trees and the visual spectacle of a large silverback feeding on ripe fruit in the forest canopy margin.
Baseline Herbaceous Diet
Across all seasons, the bulk of the mountain gorilla diet consists of leaves, stems, pith, and bark from the dominant montane forest plant species: Galium (bedstraw), Lobelia, Hypericum, stinging nettles (which the gorillas handle with the same apparent discomfort-and-tolerance balance that humans demonstrate with the same plant), wild celery, and the various thistles and herbs that dominate the forest floor. The ratio of leaves to stems varies by season — during the dry season when mature leaves are tougher and less palatable, the gorillas preferentially select young leaves and softer stems that provide the same nutritional content at lower chewing cost. The total daily food intake of an adult gorilla is approximately 18–20 kilograms of plant material — a figure that, when translated to the daily activity budget, means that mountain gorillas spend approximately six to eight hours per day feeding.
