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Clearing up mysteries about gorillas in the mist
Sunday, March 11, 2001 By Anita Srikameswaran, Post-Gazette Staff Writer
Mountain gorilla groups typically start the day by looking for a good patch of nettles, tender bamboo shoots and leafy greens, says primatologist Dieter Steklis.
When they find it, each animal sits off by itself and chows down, says Steklis, who is scientific director of the Dian Fossey Mountain Gorilla Fund International and an anthropology professor at Rutgers University.
Afterward, "the adults might nap if it's a nice sunny day," Steklis says. "The youngsters use this occasion for playing. Wrestling and chasing, the usual kind of stuff."
Adults, even the awesome mature males called silverbacks, horse around with the youngsters. Females groom the mature males and the children, or cuddle the infants. Sisters may visit new mothers and check out their babies.
The break lasts about an hour. Then the dominant male leads the others in search of another food patch. There may be more than one silverback in a group of gorillas, but only one is in charge.
Another siesta period follows lunch, and in the early evening, after another forage for dinner, the gorillas begin building nests by folding and matting down plant fronds. Each weaned gorilla makes his or her own bed, and mothers share with their infants.
Gorillas may traverse a few miles and consume up to 50 pounds of plants during the daily routine.
"They're big herbivores, and they need to get enough energy from that vegetation to fuel the bulk," Steklis says.
Occasionally, one group of gorillas comes across another in the forest. The dominant silverbacks of each may charge or, if the confrontation gets really heated, they may slap and bite each other, inflicting potentially fatal flesh wounds. Females may approach the front line intending to cross over to the other group, but are often forced back by nondominant silverbacks.
A large group may include 20 adult females and several silverbacks. Small groups may consist of only one silverback and a handful of females. Gorillas are not incestuous, so if a daughter gorilla is to mate and procreate, she must transfer to another group or a lone silverback would have to join hers, Steklis explains.
He estimates that baby mountain gorillas weigh 3 or 4 pounds at birth after an eight-month gestation. Adults are very protective and don't hand babies over to researchers for a proper weighing. After four years or so, the juvenile gorilla is weaned from its mother's breast, but remains with her for several more years until it approaches maturity.
A young male is called a blackback because it does not yet have the silver hair that marks maturity, which comes in at about age 12. A female becomes sexually mature as an 8-year-old and, on average, has a first baby at 10. She may have five or six offspring during her lifetime.
Mountain gorillas differ from the lowland gorillas you can see at the Pittsburgh Zoo in various physical ways, such as having longer hair and being bigger. They also eat different foods. For instance, gorillas from the western lowlands have diets high in fruits, which don't grow in the high altitudes that are home to mountain gorillas.
As with humans, mountain gorilla females tend to have longer life spans than the males. Researchers believe some females have lived into their mid-40s, while the males usually die in their mid- to late 30s.
Steklis says other kinds of gorillas, such as the western lowland, live into their 50s when in the protected and predictable environment of a zoo.
But you won't see a mountain gorilla in a zoo, and it's not just because researchers want to observe them in their natural surroundings or because they are protected by law.
Their numbers are large enough to safely sustain a population in the wild but so small, the loss of even a few individuals could be harmful to genetic diversity in subsequent generations. Simply put, capturing a mountain gorilla isn't worth the risk to those left behind.
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