Female chimpanzees giving first birth in their natal group in Mahale: attention to incest between brothers and sisters.

Chimpanzee societies generally show male philopatry and female dispersal. However, demographic data on wild chimpanzee societies from long-term study sites have revealed that some females give birth in their natal group (i.e., "remaining females"). Here, we report two remaining females in the M group in Mahale, Tanzania, and compare their cases with previous reports to explore the social and ecological factors that lead to females remaining in their natal group. The results revealed that neither the social traits of the remaining females nor the ecological factors they experienced showed a coherent trend. However, we found multiple, non-mutually exclusive potential factors that may influence the decision by females to remain in their natal group: a decrease in indirect feeding competition, support from mothers or allomothers in the care of offspring and in aggressive interactions with other individuals, close relationships with the other remaining females, and a short adolescent infertility period. Additionally, we observed a natal female copulating with her older brother, which was the first observation of brother-sister incest in Mahale. Although DNA analysis revealed that her infant was not a product of inbreeding, the pair copulated frequently in the latter half of her estrus period, suggesting that they did not avoid incest behaviorally to avoid inbreeding. Furthermore, there was no hard evidence that the remaining female avoided mating with her maternal brother, suggesting that incest avoidance may not be a proximate factor responsible for female dispersal.

Ranging behavior of Mahale chimpanzees: a 16 year study.

We have analyzed the ranging patterns of the Mimikire group (M group) of chimpanzees in the Mahale Mountains National Park, Tanzania. During 16 years, the chimpanzees moved over a total area of 25.2 or 27.4 km(2), as estimated by the grid-cell or minimum convex polygon (MCP) methods, respectively. Annually, the M group used an average of 18.4 km(2), or approximately 70 %, of the total home-range area. The chimpanzees had used 80 % of their total home range after 5 years and 95 % after 11 years. M group chimpanzees were observed more than half of the time in areas that composed only 15 % of their total home range. Thus, they typically moved over limited areas, visiting other parts of their range only occasionally. On average, the chimpanzees used 7.6 km(2) (in MCP) per month. Mean monthly range size was smallest at the end of the rainy season and largest at the end of the dry season, but there was much variability from year to year. The chimpanzees used many of the same areas every year when Saba comorensis fruits were abundant between August and January. In contrast, the chimpanzees used several different areas of their range in June. Here range overlap between years was relatively small. Over the 16 years of the study we found that the M group reduced their use of the northern part of their range and increased their frequency of visits to the eastern mountainous side of their home range. Changes in home-range size correlated positively with the number of adult females but not with the number of adult males. This finding does not support a prediction of the male-defended territory model proposed for some East African chimpanzee unit-groups.

Descriptive epidemiology of fatal respiratory outbreaks and detection of a human-related metapneumovirus in wild chimpanzees (Pan troglodytes) at Mahale Mountains National Park, Western Tanzania.

Over the past several years, acute and fatal respiratory illnesses have occurred in the habituated group of wild chimpanzees at the Mahale Mountains National Park, Tanzania. Common respiratory viruses, such as measles and influenza, have been considered possible causative agents; however, neither of these viruses had been detected. During the fatal respiratory illnesses in 2003, 2005 and 2006, regular observations on affected individuals were recorded. Cause-specific morbidity rates were 98.3, 52.4 and 33.8%, respectively. Mortality rates were 6.9, 3.2 and 4.6%; all deaths were observed in infants 2 months-2 years 9 months of age. Nine other chimpanzees have not been seen since the 2006 outbreak and are presumed dead; hence, morbidity and mortality rates for 2006 may be as high as 47.7 and 18.5%, respectively. During the 2005 and 2006 outbreaks, 12 fecal samples were collected from affected and nonaffected chimpanzees and analyzed for causative agents. Analysis of fecal samples from 2005 suggests the presence of paramyxovirus, and in 2006 a human-related metapneumovirus was detected and identified in an affected chimpanzee whose infant died during the outbreak. Our findings provide preliminary evidence that the causative agent associated with these illnesses is viral and contagious, possibly of human origin; and that, possibly more than one agent may be circulating in the population. We recommend that baseline health data be acquired and food wadge and fecal samples be obtained and bio-banked as early as possible when attempting to habituate new groups of chimpanzees or other great apes. For already habituated populations, disease prevention strategies, ongoing health monitoring programs and reports of diagnostic findings should be an integral part of managing these populations. In addition, descriptive epidemiology should be a major component of disease outbreak investigations.

Chimpanzee deaths at Mahale caused by a flu-like disease.

A flu-like disease spread among chimpanzees (Pan troglodytes schweinfurthii) of the M group at Mahale Mountains National Park, Tanzania, from June to July 2006. This epizootic or epidemic killed up to 12 chimpanzees. The obvious evidence of their deaths came from finding the bodies of three infants who had previously shown some symptoms of the disease. At least one of these infants died of pneumonia. In addition, nine chimpanzees were missing after the outbreak. These individuals were assumed to have been killed by this epizootic because most of them had contact with the infected individuals on the last days they were observed. We also found two dead bodies during this period, which were thought to be those of two missing individuals. We confirmed 23 (35.4%) of 65 individuals of the M group showed some symptoms of the disease, although most of them (20/23) did not die. More than half of them (14/23) had kin showing symptoms. Since this epizootic may have been caused by contact with humans, it will be necessary to establish and follow appropriate protocols for researchers, tourists, and park staff to observe chimpanzees, and to explore the mechanism of disease transmission from humans to chimpanzees and among chimpanzees.

Responses of wild chimpanzees (Pan troglodytes schweinfurthii) toward seismic aftershocks in the Mahale Mountains National Park, Tanzania.

This is the first report documenting the responses of wild chimpanzees (Pan troglodytes schweinfurthii) to seismic activities. During our long-term fieldwork in Mahale Mountains National Park, Tanzania, a high-intensity earthquake with a Richter magnitude of 6.8 occurred at 15:19 hours local time on 5 December 2005. During the main tremor, the chimpanzees displayed the "wraa" call, "scream," and "pant bark" or "bark" vocalizations. Many mild aftershocks followed the main tremor, and the wild chimpanzees displayed a variety of responses to these. In several cases, they climbed trees or stopped activities such as grooming, moving, and feeding. These responses are similar to those previously reported in nonhuman primates. During the observations, a unique behavior, one never reported before was exhibited by a female chimpanzee. She placed her right palm on the ground giving the impression she was inspecting the trembling of the ground.