Silent ambush killers
Apart from humans, leopards are the sole enemy of the chimpanzees who live in the dense rain forest of the Taï National Park. Leopards are predators that lurk or lie in wait on their prey. They do not have the endurance necessary for long chases and must, therefore, hunt their prey over short distances – an ideal hunting tactic in the dense undergrowth of the rain forest.
Leopard attacks on chimpanzees are difficult to observe, as they are deterred by the presence of humans. Over a period of five years, Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology in Leipzig documented 16 cases of injuries to chimpanzees in the Taï National Park, which could have originated in leopard attacks. In 12 of these cases, the chimpanzees managed to drive their attackers away; however, help came too late for the remaining four. It is likely that two of the killed chimpanzees were partly eaten by the leopards at a later point in time.
The research findings show that the leopards are successful chimpanzee hunters: each chimpanzee is attacked by a leopard every three-and-a-half years on average. Attacks by leopards are probably the most common cause of death among the Taï chimpanzees. Statistically, one chimpanzee falls victim to the feline predator there every 18 years.
The chimpanzees have thus developed different defence strategies to deal with this threat. Christophe Boesch discovered that the risk of attack from leopards has a major influence on the chimpanzee group size. Accordingly, chimpanzees living in areas with a number of leopards form larger groups than, for example, those in the savannah where there are fewer predatory cats. Larger groups provide better options for defence.
During an attack, the Taï chimpanzees show greater solidarity than their species counterparts in the grasslands. If an animal comes across a leopard and emits alarm calls, other group members come to its aid immediately. Moreover, they care for wounded group members intensively for weeks on end.
Attack is sometimes the best defence - and this principle holds true for the Taï chimpanzees. When the animals come across leopards, they do everything in their power to drive them away. They even avail of simple weapons for this purpose: Christophe Boesch has observed chimpanzees using branches to drive leopards away. For this reason, leopard mothers with their young also face the danger of attack. When the chimpanzees encounter a young animal, they kill it and thereby eliminate a future predator.