Washington, Feb 2 : A new study has indicated that chimpanzees are likely to hunt only when key males among the species, known as "impact hunters", are present in the group.
According to the study, these males are the ones who initiate a hunt, and hunts rarely occur in their absence.
The findings, which appear in the current issue of Animal Behaviour, shed light on how and why some animals cooperate to hunt for food, and how individual variation among chimpanzees contributes to collective predation.
The study was led by Ian Gilby, a postdoctoral researcher in the Department of Anthropology in Harvard's Faculty of Arts and Sciences, with Lynn Eberly of the University of Minnesota and Richard Wrangham, Ruth Moore Professor of Biological Anthropology at Harvard.
For this study, the researchers followed the hunting patterns of 11 adult males over more than a decade, among which two chimpanzees were identified as impact hunters. The chimpanzees that were studied live in Kanyawara, in Kibale National Park, Uganda.
"Our findings show that while hunting among chimpanzees is a group process, these individual males have a strong effect on whether or not others decide to hunt," said Gilby. "They have a strong catalytic effect on the decision to hunt," he added.
Chimpanzees live in communities of 40 to 150, within which fluid subgroups of changing size and composition form. While their diet is largely ripe fruit, chimpanzees also prey upon red colobus monkeys, which are agile and live in the trees.
According to Gilby, "When a party of chimpanzees encounters a troop of red colobus, the impact hunters tend to be the first to hunt. By doing so, they dilute the prey's defenses, thereby reducing the costs of hunting for other chimpanzees."
"Hunts rarely occurred in the absence of the impact males," he added.
Of the two impact hunters, one was the alpha male, but one was not particularly high-ranking or outstanding in terms of physical appearance.
Though it is not entirely clear what special qualities these chimpanzees might posses that would contribute to their role in hunting groups, what appears to be significant is that these particular chimpanzees display a unique willingness to hunt, and have a high success rate when hunting.
The findings of this study may also be applicable to the hunting behavior of other animals that hunt in this way, such as dolphins and lions.