October 17, 2011

Bamboo Season Attracts the Gorillas to the Park Border

With the onset of Rwanda’s biannual rains, it is time for the bamboo season in Volcanoes National Park, when many of the mountain gorilla groups monitored by the Fossey Fund’s Karisoke™ Research Center make their way down to the “bamboo belt” near the park’s border. The Bwenge, Titus, Ugenda, Kuryama, Ntambara and Urugamba groups have already been observed at lower altitudes in the park, tempted by the prospect of tasty bamboo shoots.

When the groups of gorillas converge on the bamboo zone at the border, we are bound to see two things: an increase in interactions between groups and gorillas leaving their protected forests to venture out into the surrounding farmland.

Group interactions

Two group interactions have already occurred. The first happened on the morning of Sunday, Oct. 9 in the Cundura area of the bamboo zone. Ugenda’s group encountered Titus’s group and 7-year-old female Ubufatanye transferred, lured by the displaying of Titus’ dominant silverback Umushikirano. Fortunately, the transfer occurred without any aggression. Karisoke Research Assistant Didier Abavandimwe said “Titus’s group seemed to be more interested in looking for bamboo shoots than in paying attention to the newcomer” and the female “avoided escalation of aggression from Titus’s males by touching them gently and/or keeping some distance.”

The second interaction occurred Oct. 11, when Bwenge’s and Ugenda’s groups met, also in the bamboo zone. The groups were close to the park border and both Karisoke field staff and a group of American tourists happened to be present at the time. Feeding on the bamboo and competing for this limited food source is such a high priority for the gorillas that both gorilla groups essentially ignored each other, despite their close proximity.

During the bamboo season, the Fossey Fund’s field staff has a more difficult time tracking the gorillas. Where the bamboo is prolific, there is a lack of understory vegetation that is typically examined to detect trails. The existing traces are mixed up and often indistinguishable because multiple gorilla groups forage through the same area. During this time, the field staff must rely primarily on feeding evidence to locate the groups.

Crossing the park border

The Ugenda, Titus and Urugamba groups have been observed venturing outside the park borders. The gorillas’ primary motivation for leaving the forest is eucalyptus, a highly prized food source. The light grey-green color of the eucalyptus trees punctuates the farmland surrounding the park and their tasty bark is irresistible to the mountain gorillas.

“The issue of disease transmission becomes critical when the mountain gorillas leave the park because they come in closer proximity to people and domestic animals” says Gorilla Program Manager Veronica Vecellio. The Fossey Fund’s Karisoke trackers monitor the situation closely when a group crosses the park’s stone wall border, and will stay with the gorillas until they reenter their protected forest. Occasionally, when the gorillas venture too far from the edge of the park (400 meters or more), the trackers will form a barrier and guide the group back into the forest.

Urugamba’s group was the first to cross out of the park, and trackers observed the dominant silverback charging a nearby cow. After lingering outside of the park for 20 minutes, Urugamba appeared to become stressed by the cow’s presence. When the cow started running, Urugamba gave chase before stopping dead in his tracks, apparently confused by the situation. As a result of this incident, law enforcement officers were asked to remind local people that their domestic animals should be kept at least 100 meters from the edge of the park.

There are sure to be many incidents in the coming weeks surrounding the highly anticipated bamboo season. Stay tuned!

Jessica Burbridge, Fossey Fund Field Communications Officer