June 27, 2012
End of a Busy Bamboo Season
The spring bamboo season came to an end by the third week of June. For three months, eight of the ten gorilla groups monitored by the Dian Fossey Gorilla Fund’s Karisoke Research Center had shared the bamboo zone located at the bottom of the Karisimbi and Visoke volcanoes. The season for the tender bamboo shoots to appear lasted longer than it had the previous year, starting at the end of March. Just as in the previous bamboo season in October and November, the gorillas took advantage of their close proximity to Volcanoes National Park’s edge to move out of the forest, walking through agricultural fields to find cultivated eucalyptus, which they also love.
In June, gorillas left the park eight times. Unlike the last season, the gorillas went farther than 400 meters from the park’s edge only once. This was in the case of Kuryama’s group, which was then herded back into the park by trackers, an operation that had been carried out 22 times in November. The greater abundance of bamboo shoots inside the park this time is likely to be the reason why the gorillas did not cross the park border more often to explore different resources outside.
Only Inshuti’s and Giraneza’s group (the two smallest among the groups monitored by Karisoke) did not move downhill to the bamboo zone. Even if the bamboo offers an irresistible food resource, it grows in a limited area, causing groups to come very close to each other. Consequently, encounters between two groups occur at a higher rate during the bamboo season, and that’s why Inshuti and Giraneza avoided it.
Giraneza had formed his own group at the beginning of 2012, gaining two females at the expense of Inshuti, who retained only one female and two infants. For Inshuti and Giraneza, the temptation to feed on their favorite bamboo shoots did not overcome the risk of being close to other groups and possibly losing one or more females. In particular, it is almost four months since Inshuti moved to the alpine zone of Mount Karisimbi. This is the farthest region in which a group monitored by our staff at Karisoke had lived for such a long period. Since then the monitoring of the four gorillas of Inshuti’s group has been limited to a few minutes per day, due to the long distance the field staff must walk to reach them. Because of the limited opportunity for observation, the behavioral data collection on this group has been suspended.
The bamboo zone was the location of three very long interactions between groups that took place in June. One occurred between Titus’ and Urugamba’s group and lasted two and a half hours, with all five males exchanging displays. More severe was the one between Bwenge’s and Isabukuru’s group, which lasted about three hours. Dominant Isabukuru faced Bwenge’s group alone, pushing the group for about three kilometers! The juvenile Ntaribi, from Bwenge’s group, gave proof of his courage on this occasion. He displayed to Isabukuru, facing him in a typical confrontational posture. Isabukuru wasn’t intimidated by the young gorilla and he suddenly grabbed him with his mouth, transporting the youngster for many meters. Ntaribi, terrified, immediately ran away when Isabukuru finally dropped him. After that, Bwenge’s group ran away, followed for hours by the persistent silverback.
By contrast, the interaction between Kuryama’s and Urugamba’s group was unusually calm. The two groups faced each other in the same area for one hour, apparently ignoring their close proximity. Silverback Urugamba displayed only once, but the most remarkable behavior was that of the juvenile gorillas from both groups, who played together.
In June, another gorilla took advantage of the proximity of two groups. This was subadult male Inkumbuza, who was already famous for changing frequently between Ugenda’s and Urugamba’s groups. In just a few weeks he changed groups five times (11 times since the beginning of the year).
The bamboo season also offered a good opportunity to meet lone silverbacks, who also harvested the young shoots. In May and June the field staff saw four of them ranging in the same area as the research groups, including the young silverback Mafunzo, who had recently left his natal group to start a solitary life.
As the season has now finished, the gorillas are moving from the bamboo zone, located at the bottom of the volcanoes, to their usual range at higher altitude, and their life is returning to its normal routine.
Veronica Vecellio, gorilla program coordinator