Structural analysis of behavioral freedom in free-ranging and captive chimpanzees

Behavioral freedom is becoming an increasingly important issue bridging animal welfare and conservation biology. This study focused on range size and spatiotemporal variation in Western chimpanzees, creating a novel index for behavioral freedom. Direct observations were conducted on a group of seven free-ranging chimpanzees in Bossou, Guinea, during 10-hr observation periods over 10 days, and on a group of five captive individuals at the Kumamoto Sanctuary during 7-hr observation periods over 7 days. Bossou chimpanzees showed dynamic ranging patterns; their range size was larger, and their day and time-of-day ranges did not generally overlap. Additionally, the average time-of-day range was 5.2 times greater than the day range. In contrast, sanctuary chimpanzees showed a static ranging pattern, with a smaller range size and a time-of-day range to day range ratio of 1.0. Therefore, the time-of-day range to day range ratio is a suitable quantitative index of behavioral freedom in chimpanzees.