Abstract
I compared the difference of the duration of a stroke and the stroke techniques used between primate species. I observed allogrooming of Japanese macaques (9 pairs, October, 1997, Arashiyama Monkey Park, Kyoto), chimpanzees (6 pairs, August - October, 1999 and June, 2004, Mahale Mountains National Park, Tanzania), and humans (2 pairs, July, 2000, Katunbi, Tanzania). Strokes using both hands were analyzed. Japanese macaques used palms and fingers for stroking, but humans used thumbs and forefingers. Chimpanzees stroked using thumbs, forefingers, fingers and lower lip. Chimpanzees took more time for a stroke (mean=1.3 s, range=1.0-1.5, N=6) than Japanese macaques (mean=0.55 s, range=0.30-076, N=9) and humans (0.63 s and 0.60 s). Chimpanzees sometimes spent more than 3 seconds for a stroke. On the other hand, Japanese macaques spent 2.6 seconds or less and humans spent 2.5 seconds or less. It was considered that chimpanzees need more time for searching ectoparasites around a large stroked part because they have sparse coats. However, Japanese macaques and humans could not expose such a large part of the body with one stroke because Japanese macaques have dense coats and humans who were observed have coiled hairs. Japanese macaques and humans were also thought to have shorter stroking techniques for holding unruly hair which is not necessarily activity directly used to search for ectoparasites. It was not clear how chimpanzees decide to use short or long duration strokes. I also discussed the relationship between the duration of stroke and the body size among primate species.
