Habitat and Diet
The image to the left is a mosaic of two SIR-C images obtained by Shuttle astronauts in 1994 is presented. The original images were processed and colored (slightly differently) by Dr. Scott Madry at the Rutgers Center for Remote Sensing and Spatial Analysis. Scene is about 68 km across. North is to upper left.
Habitat The image above shows the Virunga volcano chain, home to about half of the mountain gorillas remaining in the world. The pristine rainforest, shown in different shades of green in this false color image, appears as an irregular strip spanning the eight volcanoes of the chain. The forest is a small island of habitability for the gorillas surrounded by a vast sea of cleared agricultural lands, shown in light purple speckled with light green. The six volcanoes at the center and right end of the chain are dormant. The two at the left end are still very much alive, as indicated by the numerous distinct lava flows (in brown and purple) radiating from them.
There is a great span of elevation in the Virunga
Mountain habitat of the mountain gorillas, ranging from about 1,525 m (5,000 ft) on the
plains at the base of the volcanoes to over 3,965 m (13,000 ft) at the summits. The change
in temperature and rainfall with elevation gives rise to a correspondingly wide range of
forest and vegetation types. The distribution of the different vegetation types in the
rainforest around the six dormant volcanoes is shown in this map developed by the Rutgers
The dominant types of land cover are the Hagenia forest, the bamboo forest, and the mixed Hagenia-bamboo forest. There are several other types occupying small areas, such as various types of grassy meadows, mimulopsis meadows, and alpine and subalpine growths dominated by the giant senecio plants. Similar vegetation types and zonations are found on the two active volcanoes off the left edge of the map, though the forests are a little drier and divided by abundant flows of frozen lava. Left: Typical Hagenia forest with dense brush near the ground and an open canopy of trees overhead. This scene is between Mounts Karisimbi and Visoke. Photo: Courtesy of the Dian Fossey Gorilla Fund
Based on observations by George Schaller and others, the Virunga mountain gorillas live within the area shown on the vegetation map. Most of them live on the slopes of the three dormant volcanoes in the lower portion of the map (Karisimbi, Mikeno, and Visoke); the rest live around the three dormant volcanoes in the upper portion (Sabinyo, Mgahinga, and Muhavura). No gorillas live around the two active volcanoes (Nyamlagira and Nyiragongo). Even within the area shown on the vegetation map, the gorillas apparently never climb above about 3,965 m (13,000 ft) and are seldom seen in the low area between the two groups of dormant volcanoes. Interestingly, the gorillas also seem to avoid open meadow areas, even preferring to go around a meadow rather than cross it. The gorillas are found most frequently in the Hagenia forests, seasonally in the bamboo forests, and occasionally in the subalpine vegetation zone. Why? The most basic reason of all--food!
Diet Mountain gorillas are primarily vegetarians. They eat many types of plants, including the roots and stems of some plants, the leaves and flowers of other plants, and even the bark of certain trees. Right: Gorilla eating inner bark of Hagenia tree. Photo: Courtesy of the Dian Fossey Gorilla Fund
They also eat the fruit of several types of trees and vines, wild celery, thistles, the tender shoots of bamboo plants, and certain vines in their entirety.
Most of the foods gorillas eat are found year-round in the Hagenia forests--so that is where they spend most of their time. It is their primary habitat. Bamboo shoots are available only a few months of the year, usually, but not always, between August and December. The gorillas visit the bamboo forests only when fresh shoots are available. Since the growth of bamboo shoots is highly variable from year to year, depending on weather, the bamboo forest is a secondary habitat for the gorillas. The gorillas also eat the soft centers of the giant senecio trees, so occasionally they make the long hike up the mountain sides to the subalpine zone where these plants live. The other vegetation zones have little for the gorillas to eat, so they are seldom, if ever, found there. Left: This gorilla is resting amid some gallium vines, a local fast-food favorite. They eat the whole thing: leaves, stems, flowers, and berries--the works! Gorillas often take naps after eating a meal in the middle of the day. Photo: Courtesy of the Dian Fossey Gorilla Fund
For the most part, the gorillas live peacefully within the confines of the mountain forests and avoid the open, cultivated fields of the surrounding humans. Occasionally, however, mountain gorillas have been known to enter the farmers' groves to forage for bananas!
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