Photograph by Andrew Tolson
Charles used to have big rolls of fat around his neck, and chunky legs and thighs. These days, he’s much less pudgy. Charles dropped 19 lb. from June to October, which—for a 400-lb. male silverback gorilla—is no small feat. “The zoo regulars have been commenting on how good the gorillas look lately,” says Heidi Manicki Claffey, who’s been a gorilla handler at the Toronto Zoo for the past 25 years. Charles, 39, still has a big pot belly, she says, “but that’s normal for a gorilla.”
Charles is on a diet of sorts. Instead of the high-sugar, high-starch foods that zoos have fed gorillas for decades, he and the six others at the Toronto Zoo are munching on parsnips, cabbage, nuts and tofu. (As a treat, they get cinnamon-flavoured herbal tea.) This winter, for the first time, they’re also being given “browse” each day: branches they strip of edible leaves and bark, as they would in the wild. These gorillas are actually being given a greater volume of food, but they still seem to be shedding flab. From June to October, Josephine, a 40-year-old mother gorilla, dropped 22 lb.
Obesity is a growing health problem for virtually all zoo animals, from elephants to dolphins, and certainly for gorillas. In zoos, “about 40 per cent of adult male gorilla deaths are from heart disease,” which is now the number one killer of male western lowland gorillas, the only species in North American zoos, says Elena Hoellein Less, who’s finishing a Ph.D. in biology at Case Western Reserve University. Less, who works at the Cleveland Metroparks Zoo, is leading an effort to bring gorilla diets closer to what the animals eat in nature. Several zoos, including Toronto, are collaborating with her, feeding gorillas a greater volume of food—and more calories—than before, with a focus on high-fibre vegetables and browse, instead of starch and carbohydrates. This work could have implications for our own obesity epidemic, too.
Zoo gorillas live longer than those in the wild because they don’t have predators, parasites and other threats to worry about. And they have a steady source of nutrient-rich food, but it’s not what they’d eat in the jungle. Zoo gorillas are typically fed a diet of special gorilla biscuits, which can account for 15 per cent of their diet, Less says. They also get fruits and vegetables—which still tend to be higher in sugar and starch, and lower in fibre, than anything they’d eat outside the zoo—and sometimes even yogourt. “These foods deliver a lot of nutrients in a short time,” says Jaap Wensvoort, nutritionist at the Toronto Zoo. Even a banana, he says, “is very dense” for a gorilla. He calls it fast food.
Photograph by Andrew Tolson
But gorillas are, by nature, slow eaters. In the jungle, where calories are harder to come by, they spend up to 70 per cent of the day eating or foraging; in zoos, meals take up less than half that time. To fill the extra hours, zoo gorillas are given toys to play with, but “unless it’s food, they don’t really care,” says Ali Vella-Irving, another Toronto gorilla handler. Boredom could be one reason that about 65 per cent of zoo gorillas will voluntarily regurgitate their food and then eat it again, a behaviour that isn’t seen in the wild.
Even before collaborating on Less’s project, the Toronto Zoo had been tinkering with its gorilla diets. About a decade ago, “we took the yogourt and a lot of the gorilla chow away,” Wensvoort says, and added soy proteins, which protect against heart disease in humans. (Gorillas are vegetarian.) Today, they’re fed five times daily, mainly high-fibre vegetables and browse. They still get some gorilla biscuits and muffins—which deliver specific nutrients, and medication like birth control—but they get very little carbs. Higher-calorie foods, like nuts, tofu and yam, are given to each gorilla individually, so they don’t fight over them; lower-calorie foods like celery, mushrooms and leeks are spread around their enclosure, which keeps them busy.
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