When it comes to choosing a place to live, male chimpanzees in the wild don't stray far from home, according to a new report in the Dec. 27th Current Biology, a publication of Cell Press. The researchers found that adult male chimps out on their own tend to follow in their mother's footsteps, spending their days in the same familiar haunts where they grew up. Male chimpanzees are generally very social, but how they use space when they are alone might be critical to their survival, the researchers said.
"We have found that, like females, male chimpanzees have distinct core areas in which they forage alone and to which they show levels of site fidelity equal to those of females," said Anne Pusey of the University of Minnesota. "Moreover, males remain faithful to the area in which they grew up with their mother, even 20 years after she has died. Even alpha males, who could presumably compete successfully to forage in the most productive areas, instead continue to forage in the areas in which they grew up, even in cases where this area is of poor quality."
They suspect that sticking to places they know well might give chimpanzees an advantage when searching for food. The new findings therefore suggest that, even for males, the need to eat can sometimes trump sex. Because males' reproductive success depends on the number of females they can fertilize, their ranging patterns were generally thought to be driven more by access to females than to food, she said. This study demonstrates that food and members of the opposite sex both affect male space use.
The majority of studies on site fidelity have focused upon strictly territorial species in which individuals range in well-defined, exclusive areas, the researchers said. By comparison, little is known about species, including chimpanzees, that form more transient groups, lending them greater flexibility in individual space use.
Earlier studies based on indirect measures of ranging indicated that young adult male chimps seemed to continue to range near their mothers. In the new study, the researchers analyzed space use of male chimpanzees living in Gombe National Park, Tanzania, over four years. They compared the males' ranges to those in which their mothers had travelled in years past.
"Our study shows that male site fidelity persists for years after the mother has died and probably for the whole life of the male," Pusey said.
The findings raise interesting questions for future studies, she said. They plan to test whether chimpanzees really do find food more efficiently in familiar areas. They would also like to know whether males learn to follow particular diets from their mothers.
The researchers include Carson M. Murray, Jane Goodall Institute's Center for Primate Studies and Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, Minnesota, USA, and Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, IL, USA; Ian C. Gilby, Department of Anthropology, Harvard University, Cambridge, MA, USA; Sandeep V. Mane, Department of Computer Science, University of Minnesota, Minneapolis, MN; and Anne E. Pusey, Jane Goodall Institute's Center for Primate Studies and Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN, USA.