研究表明大猩猩在拥挤的森林里变得更暴力

Gorillas are very social animals -- up to a point. Crowded areas can make silverbacks more violent, scientists say.

Silverbacks are adult male mountain gorillas that often have a white area across their backs. They are the leaders of gorilla families.

Mountain gorillas are genetically similar to humans. The large animals spend most of their time sleeping, eating, and cleaning each other. They are mostly peaceful creatures.

They live in parts of Uganda, the Democratic Republic of Congo, and Rwanda.

Researchers recently studied 50 years of data from Rwanda. They found that as the number of gorilla family groups increased, so too did the of violent fights between them. Most often, silverbacks led the fights.

Some gorillas died, especially infants, or babies. These deaths, in turn, slowed population growth.

Damien Caillaud of the University of California, Davis, was a co-writer of the new study, published in Science Advances.

"Males will fight to protect the females and infants in their group, and to acquire new females," he said.

The study found that the amount of fighting was not a result of the total number of individuals in an area. What was important was the number of family groups in an area.

Since the 1960s, mountain gorillas have been carefully studied and protected in central Africa. These animals almost died off in the 1970s. The population has since grown to just over 1,000 animals.

Rich Bergl is a primatologist at the North Carolina Zoo. Bergl was not involved in the study.

"Rarely do we think about how an animal's behavior and social structure can influence population size," Bergl said. He added, "But it turns out we should, especially for social animals like gorillas."

Tara Stoinski was a co-writer of the new paper. She is also president of the Dian Fossey Gorilla Fund, a noNPRofit group.

"Everyone wants to know how many gorillas can live inside the protected habitat area. It turns out the answer depends partly on how they organize themselves socially," she said.

While in Rwanda, Stoinski said she saw changes in gorilla behavior beginning about 2007. Around that time, three large family groups broke into many smaller family groups.

The gorilla population grew and families spread out in Volcanoes National Park.

There were about 10 family groups in the study area. The number of fights between them increased by three times. The number of infant deaths increased by five times. The population growth fell by half.

The large family groups likely broke apart after the deaths of important silverback leaders, said Stoinski.

"When these ‘elder statesman' gorillas got older and died, the younger males weren't able to keep the groups together," she said.

The study was based on data from about 400 gorillas in Rwanda between 1968 and 2017.

I'm John Russell.

Christina Larson reported on this story for the Associated Press. John Russell adapted it for Learning English. Caty Weaver was the editor.