We observed the E1 group (unit-group or community, van Elsacker et al. 1995) of wild bonobos at Wamba in the northern section of the Luo Scientific Reserve, D.R. Congo. The history of E1 and the details of the study site are described by Furuichi (1989), Kano (1992), Hashimoto et al. (1998, 2008), and Idani et al. (2008). In January 2005, E1 included 10 adult males, 6 adult females, 1 adolescent female, 2 juvenile females, 3 infant males, and 1 infant female. Hashimoto et al. (2008) have described the more recent changes in membership of the group.
We observed E1 from September 2003 to December 2005. We attempted to locate parties of E1 and to follow them from sleeping site to sleeping site 6 days per week, for a total of 711 days. During this time, we directly observed bonobos for 484 days, or 68% of the total working days. The total time of direct observation, excluding time spent tracing bonobos by footprints or vocalizations, was 2,216 hours. On average, bonobos were within sight of observers for 4.6 hours per day on days we conducted direct observations.
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