Detailed descriptions of each community can be found under the “chimpanzees” menu item. Briefly, there are three and perhaps four separate chimpanzee communities in the reserve. In the middle of the reserve the study population is found along the flanks of the Mugiri River and its tributaries. In the far northeast a separate community, though certainly much reduced if not eliminated by habitat destruction, can be found along the banks of the Muzizi River. In 1998 nests were still to be seen there, but since then the forest had been virtually destroyed by illegal logging; it is not certain that any chimpanzees survive.
In the west a population can be found in forests flanking the Nyabaroga Valley. Pant-hoots are still heard there by Reserve staff, and there is no reason to believe the individuals there are threatened.
Chimpanzees are often seen and heard along the Wasa River, but it now seems likely that these chimpanzees are part of the Mugiri community.
Mugiri Community
The chimpanzees of the Mugiri community face four unusual environmental challenges. First, as with all the Semliki chimpanzees, their habitat is dry, sunny and open; most chimpanzees live in forests where the forest floor is damp and dark. Second, their home range is immense, more than 75 sq. km, ranging from the Jogo Jogo swamp to the north to the Wasa River in the south, west to the limits of the Murigi River gallery forest edge, and east to the reserve boundary and beyond. Theirs may be the largest range of any chimpanzee community. Third, their range includes the escarpment, which means chimpanzees range from the rift valley floor up to the very top of the escarpment, more than a 1,000 m higher in elevation. Foraging parties sometimes in move from the rift valley to the top of the escarpment in the same day. Fourth, their habitat is diverse, since it encompasses flooded forest to the north, bushland and wooded grassland on the escarpment to the east, woodland lower on the escarpment, and riverine forests. Their preferred habitat is the riverine forest, which means that in some sense their habitat is one long, narrow forest. Thus resources are widely dispersed, and this puts unusual stresses on the maintenance of social ties.
Chimpanzees are seen sporadically near the lodge, in the Wasa Riverine forest. We once thought that this was a separate community, since when we encounter these chimpanzees they seem less accepting of human contact than individuals we see in the Mugiri. We have long known that these chimpanzees disappear for months at a time. For years we thought they were disappearing to the west, but after year of tracking we have concluded that they are actually the same chimpanzees we see in the Mugiri, or at least some of them are. Perhaps they are more fearful of humans when they’re in the Wasa because it is less common for them to encounter humans there, and because the forest sparser and more open. Still, we are not absolutely certain the Wasa chimpanzees are part of the same community as our study group. They appear rarely enough in the Wasa that we have never gotten a positive ID on any individual there.
The largest party1 in the study area observed so far contained 43 individuals, and with those 43 in sight we could still hear other community members calling some distance away. A rough rule of thumb for estimating community size is that there are twice as many females as males, and about as many juveniles as females. We have identified 29 males so far, but hardly any females. However, if the community contains 30 males, 60 females and 60 juveniles, which our rule of thumb would suggest, the Mugiri community would have 150 individuals, among the largest known.
Chimpanzee community subgroups are more properly referred to as ‘parties,’ rather than groups.
Nyabaroga Community
The Nyabaroga valley shares some things in common with the Muzizi. The valley is the reserve boundary, which means the west side of the valley is outside the reserve, while the eastern half is in the reserve. The chimpanzees of this community were more fortunate than the Muzizi chimps. When Semliki was being surveyed by the Uganda Wildlife Authority Boundaries Committee, they were amenable to changing the boundary of the reserve to include more of the Nyabaroga valley. The area where chimpanzees were found was very nearly unpopulated, and local authorities were willing to discuss giving up some land to the reserve. On September 3, 1997, UWA Boundaries Committee representative Richard Lamprey and Prof. Hunt walked a proposed border with representatives of the local government. At that time a large number of families were illegally living in the Kyabandara area of the reserve. Many of these people claimed to have been displaced when the Rwenzori National Park was created. In any case, the authorities agreed to swap the degraded and heavily populated Kyabandara area for a 5 sq. km area of the Nyabaroga. Prof. Hunt heard abundant pant hoots in Kyabandara in 2010, and rangers report that chimpanzees are often seen in the area, and occasionally crossing the road that runs through the reserve in the area.
The Nyabaroga area is at most a third the size of the Mugiri community area. It is a mosaic of forest, open woodland, and wooded grassland, slightly denser on average than the Mugiri area. It might support a community of 50 individuals. The population seems relatively safe, and UWA rangers still report pant-hoots there. It would benefit from either tourist development or an active research project, either of which would offer monitoring of the area and allow a thorough census of the community.
Muzizi Community
The Muzizi River marks the eastern half of the northern boundary of the reserve, and as such the forest flanking the northern bank of the river is outside the reserve, while the southern half in inside. The southern banks of the Muzizi are on the side of the river closest to the fishing village of Ntoroko, and the point where the Muzizi meets Lake Albert is literally only hundreds of meters from Ntoroko. Ntoroko grew steadily in the 90s, and much faster in the 2000s. With such growth inevitably natural resources nearby are strained. In 1996 and 1997 Prof. Hunt visited the Muzizi River forest several times and heard pant-hoots and saw chimpanzee sleeping nests. At that time some areas were completed deforested by illegal logging, but other areas were less seriously degraded, and still other areas appeared to be relatively undisturbed. Over the next few years much of the forest on the northern bank of the Muzizi was logged. Charcoal was sold in abundance on roads nearby, presumably made from wood logged in the Muzizi forest.
Chimpanzees can live in degraded forest—both of the other dry-habitat chimpanzee sites are in areas with human occupation—so even with perhaps half of the habitat destroyed, chimpanzees were still hanging on in the late 90’s. In 2008 SCP assistant Tim Webster visited the Muzizi forest to check on the status of the community there for the first time since Prof. Hunt had visited in 1999. Webster reported that the forest was completely gone. Satellite imagery from 2011 shows that some forest remains, some within 100s of meters of bare areas. Chimpanzees could certainly live in reduced numbers in the area, and the forest could make a recovery if it were properly managed.