PRIMATES, 37(4): 389--397, October 1996 389 Anti-predator Behavior of Gelada Baboons TOSHITAKA IWAMO'IO, Miyazaki University AKIO MORI, Kyoto University MASAO KAWAI, Nihon-Fukushi University and AFEWORK BEKELE, Addis Ababa University ABSTRACT. The anti-predator behavior of gelada baboons has been observed to consist of simple flight (i.e. they flee to cliffs after becoming alarmed by potential predators). However, active anti- predator behavior was observed in a recently found gelada population in Arsi, Ethiopia. This population showed frequent active counter-attacks and severe mobbing at predators. Males fought domestic dogs on the plain and exhibited a systematic mobbing behavior towards a leopard on the cliff face to chase it off. These active anti-predator behaviors are the first confirmed reports on gelada baboons and may provide a useful insight for the understanding of the process of evolutionary adaptation to highland habitats by gelada baboons, as well as for the origin of this small southern population. Key Words: Theropithecus gelada; Anti-predator behavior; Predation; Mobbing. INTRODUCTION Gelada baboons (Theropithecus gelada) inhabit a highland plain bordered by cliffs at altitude of 2,000-4,500 m in Ethiopia. They feed in the grassland of the plain in the daytime and spend nights on the cliff face (CROOK & ALDRICH-BLAKE, 1968; KAWAI & IWAMOTO, 1979). A considerable amount of observation has been accumulated on the social structure (CROOK, 1966; KAWAI et al., 1983; DUNBAR, 1993) and feeding ecology (DUNBAR, 1977; IWAMOTO, 1979, 1993; IWAMOTO & DUNBAR, 1983), but no intensive obser- vation has been made on their anti-predator behavior. There are very few studies on their anti-predator behavior mainly because of their simple avoidance of predators. They rarely show active defense against predators and generally flee to the cliffs while making alarm barks (OHSAWA, 1979; IWAMOTO, 1993). Sleeping on the cliff face at night is also considered a passive anti-predator behavior because the site is too steep for predators. Several reproductive units (one-male unit) form a band with relatively loose relationships, and a few bands sometimes aggregate to form a large temporary "multi-band" of up to several hundred geladas (CROOK, 1966; OHSAWA, 1979; KAWAIet al., 1983). This aggregation is also regarded as another passive anti-predator behavior in order to detect predators as early as possible, when they spread deep inside the plain (IWAMOTO, 1993). These passive anti-predator behaviors differ clearly from those found in other savannah-living baboons (ALTMANN & ALTMANN,1970; COWLISHAW, 1994). MORI and BELAY (1990) reported a new gelada population on the fringe of the southern Ethiopian highlands south of the Great Rift Valley. This was contrary to the general belief that gelada baboons inhabited only the northern highlands, north of the Rift Valley (YALDEN et al., 1977). Since the Rift Valley that was formed in the late Pliocene (3.5 - 2.5