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This study reports the first observed case of wild chimpanzees (Pan troglodytes) obtaining animal prey freshly killed by a sympatric leopard (Panthera pardus) and scavenging it with the leopard still nearby. This observation has important implications for the emergence of confrontational scavenging, which may have played a significant role in human evolution. Many scholars agree that eating meat became important during human evolution, and hominins first obtained meat by scavenging. However, it is debatable whether scavenging behavior was "passive" or "confrontational (power)." The latter is more dangerous, as it requires facing the original predator, and it is thus considered to have been important for the evolution of several human traits, including cooperation and language. Chimpanzees do scavenge meat, although rarely, but no previous evidence of confrontational scavenging has hitherto emerged. Thus, it was assumed that they are averse to confrontation with even leopard-sized predators. However, in the observed case the chimpanzees frequently emitted waa barks, which indicated that they were aware of the leopard's presence but they nevertheless continued to eat the scavenged meat. In addition, we compiled and reviewed 49 cases of chimpanzee encounters with animal carcasses in the Mahale Mountains of Tanzania in 1980-2017. Chimpanzees scavenged meat in 36.7% of these cases, and tended to eat the meat when it was fresh or if the animal species was usually hunted by chimpanzees. However, no evidence indicated that carcasses were avoided when leopard involvement was likely. These results suggest that chimpanzee-sized hominins could potentially confront and deprive leopard-size carnivores of meat.

Leopard diets in the Kasoje area of the Mahale Mountains National Park, Tanzania, were analysed by inspecting prey remains in 256 scats. This area is unique as leopard density is high despite a relatively low density of medium‐sized ungulates, regarded as the most preferred prey of leopards. At least eleven prey mammal species were confirmed in the scats. Small prey mammals up to 10 kg comprised 91.4% of the relative biomass consumed; the mean prey biomass in each scat was 7.6 kg. Blue duiker (31.2%) was the most dominant prey species, followed by the red colobus (29.2%), semi‐terrestrial Cercopithecinae (the vervet monkey and yellow baboon combined) (10.5%) and the red‐tailed monkey (9.9%). At the order level, the most consumed prey taxon was Primates (53.8%), followed by Cetartiodactyla (39.6%) and Rodentia (5.8%). Among primates, the blue monkey was the most preferred prey species, followed by the red colobus and semi‐terrestrial Cercopithecinae. High consumption of primates is a unique characteristic of the leopards in Mahale. This trend exemplifies the flexibility of leopards in their choices of prey, and such flexibility may be one of the underlying reasons for leopards exhibiting the broadest global distribution among all wild felid species.

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The activities of predators and prey have been reported to influence each other. However, few studies have clarified when African leopards Panthera pardus are likely to encounter their prey. One reason for this is that the activity patterns of African forest mammals are poorly understood. Therefore, I aimed to clarify the activity patterns of leopards and their prey species by deploying camera traps on the ground and in trees in Mahale Mountains National Park, Tanzania. In total, 4468 camera days of camera traps set on the ground and 286 camera days of camera traps set in trees were analyzed. The overlap in activity patterns between leopards and their main prey species was calculated using coefficient Δ. At least seven leopards were identified in the study area. Leopards were active throughout the day, with crepuscular peaks at dawn and dusk. Blue duikers Philantomba monticola, the most consumed species in Mahale, were predominantly diurnal. The activity patterns of leopards moderately overlapped with those of blue duikers (Δ = 0.65). The activity patterns of leopards showed a moderate (Δ = 0.61) or low (Δ = 0.42) overlap with those of red‐tailed monkeys Cercopithecus ascanius when detections were captured by arboreal or terrestrial cameras, respectively. Mahale leopards may hunt blue duikers and arboreal primates in the midday on the ground, and may also attack primates in roost trees at night. Future studies on the leopard diet in various study areas, as well as comparisons of activity patterns between leopards and other animals, will elucidate leopard ecology.