SCIENCE / MEDICINE : Baby Boom : Gorillas: Zoologists try to create natural habitats and learn more about the primate’s behavior in order to create an environment conducive to breeding.
It has become almost a truism in zoology that the more complicated an animal’s lifestyle is in the wild, the less likely it is to be willing to do something simple, like reproduce, in captivity.
This has certainly been the case with the gorilla, a species that shares about 98% of human DNA but, until recently, has shown remarkably little inclination to pass much of it along to offspring in zoos.
However, that situation is changing. As the gorilla’s numbers continue to decline in the wild, there are encouraging signs that new zoo strategies for safeguarding its future in captivity are beginning to pay off.
Zoos routinely had used artificial insemination and forced cohabitation in often unsuccessful attempts to get gorillas to breed. Now they are designing naturalistic habitats and conducting behavioral studies in an effort to get captive gorillas to do what comes naturally to their wild cousins.
And it seems to be paying off.
“In 1985, for the first time, there were more gorilla births than deaths in zoos,” said animal behaviorist Thaya duBois, assistant director of research at the Los Angeles Zoo.
To ensure that this trend continues, zoos are stepping up their collaborative efforts.
In 1983, the American Assn. of Zoological Parks and Aquariums established a species survival plan for the lowland gorilla, a close cousin of the mountain gorilla studied by the late Dian Fossey, and the variety commonly found in zoos. Across the United States, zoos that had competed fiercely for gorillas now participate in transfer and exchange programs aimed at avoiding inbreeding and at exposing the easily bored and often choosy great ape to novel situations and a fresh selection of mates.
“The new spirit of cooperation with which zoos have approached this problem is overwhelming,” said Dr. Terry Maple, who conducted pioneering studies of the lowland gorilla at the Yerkes Primate Research Center before becoming director of Zoo Atlanta in 1984.
While he was at Yerkes, Maple and a colleague, Michael Hoff, drew up guidelines on gorilla care that have been adopted by many zoos. Heading their list was the recommendation that gorillas in captivity be housed in surroundings closely modeled on their natural habitat. Ideally, gorilla exhibits should satisfy the animal’s “tendency to consume its organic environment,” Maple said at the time. He cited San Diego’s Wild Animal Park and Seattle’s Woodland Park Zoo as models for other zoos to follow.
Today, a number of zoos have naturalistic enclosures that allow gorillas to roam and forage. In 1988, under Maple’s leadership, Zoo Atlanta joined the “habitat immersion” ranks, moving 10 gorillas into Tropical Rain Forest, a multimillion dollar replica of their African habitat.
“I’m probably the only zoo director in the world who’s been given the opportunity to put suggestions he made from the sidelines into practice,” Maple now says. He called the Atlanta exhibit “the state-of-the-art effort to give gorillas in captivity some of the control over their lives that they have in the wild.”
In the wild, as Fossey discovered, gorillas live in small, close-knit groups, generally made up of a dominant silverback male, his modest harem of breeding females, and assorted juveniles. Ever since Fossey identified this domestic arrangement, zoos have tried to organize their gorillas in the same way.
At Zoo Atlanta, Maple has taken this concept a step further. There, four gorilla families live side by side. They are separated by barriers to prevent possible altercations among the silverbacks, but are able to continually see, approach and indirectly interact with one another.
Maple believes that this proximity, which mirrors the distribution of wild gorilla bands, may promote breeding by fueling competition among the dominant males. “Hypotheses like this are extremely difficult to test,” he said. “I can tell you that three infants have been born at the zoo since the animals moved in.”
Even without substantially changing habitat design, some zoos have been able to dramatically increase their gorilla population by carefully monitoring and analyzing their gorillas’ behavior. At the Los Angeles Zoo, where 12 gorillas live in groups of six each in two spacious enclosures, such a study has been under way since 1981.
Animal researcher duBois and the zoo’s director of research, Dr. Cathleen Cox, started the project in an effort to understand how the dynamics of gorilla social behavior might be related to greater breeding success, and to gain insights about gorilla society in general.
Now one of the longest running projects in the world, the study involves two research assistants and several trained observers, who keep daily records of more than 150 distinctive gorilla activities, ranging from chest beating and bluff charging to a flirtatious gesture known as the “haunch-scoot.”
“Primate societies are generally so complex,” said Cox, “that only long-term observational studies are likely to reveal what patterns of behavior are an essential part of the animals’ social lives. Short-term studies usually do not tell the whole story; and primate studies in zoos have mostly been short-term.”
According to duBois, who now oversees the project, those observed patterns have helped the zoo’s gorilla watchers to make appreciable differences in the gorillas’ breeding habits. One female who had been reluctant to mate developed a whole new outlook after the zoo reunited her with a more experienced, less-inhibited female gorilla, who had been a childhood companion. Both are now rearing their own infants.
The zoo also has successfully reformed a silverback named Chris, whose history of violent behavior at a former zoo included a fatal attack on his habitat mate. After observing his behavior for months, and consulting with the keepers who dealt with him on a regular basis, the researchers introduced not one, but two tough-minded mature females into his territory. “The two didn’t exactly gang up on Chris,” duBois reported, “but they formed a kind of coalition that kept him in line.”
Eventually, the former delinquent settled down and went on to father four children, two of whom now share his enclosure.
Using such strategies, the zoo has presided over the births of five infants at Los Angeles since 1985. Three of these youngsters are being reared by their mothers in their gorilla groups. The other two, after spending their early months in the zoo nursery, have been transferred to other zoos.
Gorilla mothers raising their own children are a recent phenomenon at zoos, duBois said. In addition to their breeding difficulties, gorillas who do produce children have been reluctant to nurture them. In the past, about 80% of such youngsters have spent their formative years among humans in zoo nurseries.
Today, however, most experts believe that early exposure of young gorillas to their mothers, or--if that is not possible--to their peers, has a critical impact on how well they will relate as adults to their own species. The Los Angeles researchers are monitoring how their young gorillas integrate into adult society and how social skills are being passed from one generation to another.
The researchers have found that gorillas should be allowed to remain with their social groups while giving birth; and that the presence of older, curious gorillas, far from jeopardizing the mother-child bond, as was once thought, appears to strengthen it, by making the mother far more protective of her baby. At the same time, other juveniles are keenly interested in infants, suggesting that it is at this young age that they begin developing attitudes crucial to their success as parents.
Like humans, gorillas are so individual that it is difficult to draw many general conclusions about their behavior, said duBois. The significance of certain behaviors in captive situations can also be very difficult to interpret. One intriguing case she cites concerns a lively female named Cleo, who leaped over the barrier separating the zoo’s two gorilla exhibits one night, struck up a relationship with the silverback next-door and became pregnant.
This behavior hasn’t been reported in captivity before, duBois said, but it looks strikingly like the way females in the wild emigrate out of their native gorilla bands into other groups when they are ready to mate.
“It’s precisely these kinds of behaviors that zoos need to create more opportunities for,” she said.
GROWING GORILLA POPULATION
The gorilla population in North American zoos has risen steadily since the mid-1980s, when an emphasis was placed on increasing the number of babies born and decreasing deaths.
Since 1986, 48 gorillas have been born in captivity, but only 21 have died. Gorillas are no longer captured in the wild; the seven transferred were from German zoos.
1987 1988 1989 Total Population 283 292 302 Births 15 16 17 Deaths 5 9 7 Exchanges 5 2 Net 15 9 10+ Increase
Source: Dan Wharton, New York Zoological Society from the North America Regional Stud Book of the Western Lowland Gorilla.
