Mountain gorillas friendly with neighbors outside of core home ranges

Oct. 28 (UPI) -- Mountain gorillas are surprisingly neighborly.

According to a new study published Wednesday in the Journal of Animal Ecology, mountain gorillas act friendly with neighboring gorillas, as long as they stay out of the "core" parts of their territory.

Mountain gorillas occupy what scientists call a "core home range" and a wider "peripheral" range. The apes organize themselves in close-knit groups -- eating, sleeping and playing within each range.

Sometimes, groups of mountain gorillas split permanently. When they do, closely related gorillas can find themselves living apart after years of companionship.

The latest study showed old friends and relatives recognize one another years later. Researchers found groups of mountain gorillas that once lived together are four times more likely to be friendly with one another, even a decade after a group's split.

Non-group members aren't tolerated in the core home range, no matter what. But in the peripheral range, familiar neighbors mingle peacefully.

Scientists arrived at their conclusions after analyzing 16 years worth of data on the simultaneous movement and interaction patterns of 17 mountain gorilla groups in Rwanda's Volcanoes National Park.

"Meetings of groups are fairly rare, and at first both groups are usually cautious," Robin Morrison, a biological anthropologist with the University of Exeter's Center for Research in Animal Behavior, said in a news release.

Upon meeting, gorillas often beat their chests to demonstrate strength. Interactions can either turn aggressive, with fighting and yelling, or they turn friendly -- or what scientists call "affiliative."

"In affiliative interactions, the initial tension passes and the groups intermingle," Morrison said. "They may rest together, and younger gorillas will often play with youngsters from the other group."

Humans maintain friendly relations and cooperate with large numbers of individuals outside their immediate groups. Some scientists have theorized that the evolution of this socializing pattern allowed humans to take advantage of shared resources and space without the risk of violence.

Scientists suggest their study of mountain gorillas supports such a theory.

"The pattern we found mirrors what we see in humans," Morrison said. "We also have concepts of public spaces outside our 'range' where we tolerate anyone, spaces like our homes where we tolerate certain individuals, and private spaces within those homes reserved for close family or just ourselves."

The latest findings could also aid conservation planning. Mountain gorilla numbers are actually growing, thanks to effective conservation efforts, but the species' available habitat is shrinking. The species have less than 300 square miles of habitat remaining.

"Understanding how groups interact and share their limited space is important for estimating future population dynamics and trends in this endangered species," said study co-author Jean Paul Hirwa, gorilla program manager at the Dian Fossey Gorilla Fund.