A  silverback mountain gorilla carries her twins.

A silverback mountain gorilla carries her twins. (STEVE TERRILL/AFP/Getty Images)

Kabatwa, a silverback mountain gorilla, carries her twins in the Virunga Mountains, just outside Volcanoes National Park in Rwanda. The babies were born in February. According to a 2010 census, the total number of mountain gorillas has increased by a quarter over the past seven years to reach more than 780 individuals. Two-thirds of them are found in the Virunga chain that straddles Rwanda, Uganda and the Democratic Republic of Congo. They were brought to the world's attention primatologist Dian Fossey.