Last year, a silverback alpha male gorilla, the leader of his group, and three females were shot and killed in Virunga national park, in the Democratic Republic of Congo. Two of the females had babies and the other was pregnant. The two babies were not found, and experts say they will probably have died of stress and dehydration.

This was the seventh killing in the Virunga area, which is home to 200 of the world's remaining 700 mountain gorillas. It is thought that these killings are not the work of poachers, because the bodies were left intact. Likewise, at a previous scene of slaughter, a baby gorilla - worth thousands of dollars on the live animal black market - was found clinging to its dead mother.

The motivation for the killings is not known, but it is suspected to be political. The local - and illegal - charcoal industry clashes with conservation efforts in the area, and rangers have been threatened, tortured and killed as a result of the clashes. More than 100 rangers have lost their lives trying to protect the gorillas of Virunga. The Congolese rangers in this group are working with WildlifeDirect, a conservation organisation, and they receive a salary based on donations (wildlifedirect.org).

But the mountain gorillas now face an even more uncertain future. In October this year, rebels loyal to Laurent Nkunda seized the headquarters of Virunga national park. The park's 50 rangers, in fear for their own lives, were forced to flee, leaving the gorillas unprotected.