Western Lowland Gorilla

The results, detailed in the current issue of the science journal Current Biology, may help to explain curiously peaceful interactions among neighboring social groups. The groups were observed in new behavioral studies of the western lowland gorilla (Gorilla gorilla gorilla).

1. The study could also provide clues about the role and development of kinship in early human society, say researchers behind the work. Despite being the most numerous kind of gorilla, the western lowland gorilla species is the shyest and least understood. Up to a hundred thousand western lowland gorillas are thought to inhabit the forests of central Africa.

2. Aggressive Interactions

Most knowledge of gorilla behavior comes from studies of the eastern mountain gorilla (Gorilla beringei beringei), found mostly in Rwanda and Uganda. In that species several reproductively active mature males (silverbacks) may remain within the group in which they were born for life. And among the eastern mountain gorillas, it is the females that migrate when mature.

Competition among eastern mountain gorilla groups for females can therefore be fierce, and levels of aggression among males in neighboring mountain gorilla groups can be extremely high.

Studies have revealed that male mountain gorillas engage in displays of aggression over 90 percent of the time when neighboring groups come in close contact These spectacular male-to-male displays often involve chest beating, charging, and hooting. One in five displays may culminate in physical violence,

Studying lowland gorillas has proved more difficult than studying their mountain counterparts. The dense, flat forests that lowland gorillas call home do not provide them the long-range visibility that allows mountain gorillas to spot researchers from afar and slowly get used to their presence.

In the past few years Doran-Sheehy has documented neighboring groups of western lowland gorillas feeding alongside one another in swamps and other habitats. "Females from one group may move along and sit right by the silverback from another--the two groups are totally nonchalant, just hanging out," Bradley said. "You would rarely see this kind of behavior in mountain gorillas."

To complement behavioral observations, Doran-Sheehy, Bradley, and others collected DNA from gorilla hair and dung left in night nests of 12 western gorilla groups. Genetic data is important to help understand the mating system and dispersal patterns of species. The data is also Grueling Journey

Paternity tests performed in Leipzig on DNA from silverback hair and dung samples revealed that many western gorillas (especially those in directly neighboring groups) are related as half or full brothers or as fathers and sons. "Our results suggest that males have to leave their group to acquire females, but they don't go far,

Western gorilla