Ruth Thomsen

Male Masturbation in Free-Ranging Japanese Macaques

We studied masturbatory behavior of males over a 14-mo period in free-ranging Japanese macaques (Macaca fuscata yakui) on Yakushima island, Japan. We distinguished 2 types: (1) masturbation only and (2) masturbation with final ejaculation. Both types occurred in all 15 adult troop males. We calculated masturbation only as an index (M/h). It occurred over the whole year; however, it was more frequent during the mating than during the non-mating periods. Masturbation with ejaculation was restricted to the mating period. Male mating success correlated positively with social status. Both rate of masturbation only and masturbatory ejaculations increased as male social status and male mating success declined. Lower-ranking males had higher rates of masturbation only, i.e., they spent more time masturbating than higher-ranking males did. Lower-ranking males also had higher proportions of ejaculates for masturbation, while higher-ranking males used most of their ejaculates for mating.

Sniffing behaviours in guenons.

In Old World monkeys (OWM), the olfactory sense is thought to be less important than in other primate taxa. However, during the last decade experimental studies have shown that OWM possess much better olfactory capabilities than suspected. Here, we investigate for the very first time sniffing behaviours in three guenon species (Diana, de Brazzas and owl-faced monkeys) held in the Leipzig Zoo, Germany. We recorded frequencies and contexts of sniffing. The sniff index was used to allow comparisons across species. It was found that individuals sniffed 6.12 ± 7.69 times per hour. Most sniffing occurred in food-related contexts. Furthermore, Diana monkeys sniffed less often than de Brazzas and owl-faced monkeys. Thus, natural selection may drive the differences in using the olfactory sense in closely related primate species.