Chewing the Scenery

Springtime brings human locavores to the farmers market to browse for fresh greens. Meanwhile, the chameleons, chimpanzees, and alpacas (pictured above) living at Lincoln Park Zoo are eating right from the backyard

Chimpanzees and gorillas enjoy mulberry leaves, willow branches, and grapevines. Tortoises go nuts for homegrown hibiscus flowers. And the alpacas and camels? “They’ll eat pretty much anything,” says Katrina Chipman, director of horticulture. “They’re like giant goats.”

Red-footed tortoises forage on fragrant hibiscus flowers at Regenstein Small Mammal-Reptile House.

Providing fresh leaves and other plant parts—what zookeepers call “browse”—has been a priority for Chipman and Nutrition Center Manager Karina Carbo. Carbo’s hope is to supplement the grain-based food most zoo animals eat with at least 1–2 percent of fresh greenery. “It has higher fiber content,” she says. “It takes longer to eat. It’s a more wild type of diet.

In the past, keepers fed animals browse when they got the chance—for example, when shrubs were being pruned. Now, improving the natural relationship between animals and plants is part of the garden plan. Small browse gardens are being expanded. Chipman is working with Carbo; Allison Kao, manager of enrichment and behavioral husbandry; and the zookeeping staff to grow appealing plants that improve the animals’ diet and help enrich their lives

Plants for Habitat

The gardens already supply habitat. In Helen Brach Primate House, black-and-white colobus monkeys scamper up branches from trees on the grounds. In McCormick Bird House, nests are built from local twigs and wisps of greenery. Peccaries—wild pigs—like to root around stumps. “Stumps have lots of nooks and crannies,” says Chipman. “It gives the animals more complexity to explore.”

New plants to smell, touch, and taste are a stimulus for the animals. Even Siku the polar bear enjoys leafy branches in his enclosure, although “he likes playing with them more than eating them,” Carbo says.

Keepers often spread browse around an enclosure or tuck it in out-of-the-way places so the animals can experience the mental challenge of finding it. In Regenstein Center for African Apes, each new stick is a new tool for chimpanzees as they fish for hidden food.

A stick doubles as a toothpick and insect-foraging tool for a chimpanzee at Regenstein Center for African Apes.

“When you see the animals engaging in natural behaviors and eating, it’s very satisfying,” says Chipman.

Using wood and leaves for the animals also helps avoid the need to discard waste from the gardens, an important tenet of sustainable gardening. “Whatever we can’t use, we grind up for mulch,” she says. “We want to recycle and reuse everything.”

Finding a Way

There are challenges to growing plans for the sake of animals. One is figuring out which animals like to eat what, Chipman says. Keepers are now keeping track of which plants animals seem to prefer, so she can try to figure out how to grow or scrounge more of them.

She can’t plant whatever she likes. All browse plants must be approved by Kathryn Gamble, D.V.M., the zoo’s Dr. Lester E. Fisher Director of Veterinary Medicine, to make sure they are safe.

She also reviews ornamental plants for the gardens and the exhibits to guard against the chance that a harmful plant might find its way into an animal’s enclosure. For example, any plant in the allium family—such as onions, garlic, or the huge purple globe alliums that bloom just after the tulips—is toxic for carnivores. Plants to be grown in or near an exhibit—such as the trees and shrubs a 19-foot-tall Baringo giraffe is able to reach from Regenstein African Journey’s Kovler African Savanna—are carefully screened.

Zoo horticulturist David Lutz prunes plants in a zoo browse garden.

Even if a plant grown for browse is safe, it may not be appetizing. Rhinos did not evolve to eat plants that grow well in the Chicago climate, Chipman points out. Yet evolution is not necessarily a reliable guide. Animals from around the world seem to enjoy the tender little leaves of honey-locust, although it’s a Midwestern native tree.

Everything Chipman plants at the zoo must be able to survive Chicago’s erratic springtimes; hot, humid summers; and cold winters. Those winters shut down the fresh browse supply. Instead, animals get frozen grape leaves and other plants kept in a walk-in freezer. “The animals don’t love it as well as fresh browse, but they will eat it,” says Carbo. A crew of volunteers helps greatly with the time-consuming work of packing browse for freezing.

The Volunteer Enrichment Group’s Barb Jackson and Jenna Lieblich process browse for frozen storage, which allows apes such as herbivorous western lowland gorillas to receive it year-round.

Growing for browse changes the way the horticulturists care for plants. “Constantly removing plant material depletes the soil,” says Chipman, because the plant has to absorb more nutrients to regrow the leaves and branches that were harvested. Like farmers, the horticulturists must replenish the soil’s fertility. They apply a mulch of composted leaves, collected from the zoo’s trees. The mulch layer will be slowly broken down by soil organisms to resupply nutrients. Meanwhile, it also suppresses weeds that would compete with the browse plants

A Small Urban Garden

One big limitation for browse growing is Lincoln Park Zoo’s small size. Some zoos have entire farm fields, but here, browse gardens are small patches among the formal garden beds. Several kinds of hardy bamboo, beloved by gorillas, now grow near the carousel and behind  Regenstein Birds of Prey.

To supplement what the horticulturists can grow on site, they harvest willow branches from the Diversey Driving Range just north of the zoo. They also are experimenting with pollarding and coppicing—traditional pruning techniques used to push trees to increase production of new, tender twigs and branches.

Keeper Michael Richlak distributes browse for the Bactrian camel herd.

Growing for the animals shapes the plans for the zoo’s entire grounds. “In the gardens, whenever we can add a plant, we try to make it something we can harvest for browse,” says Chipman.

From the stately leaf-eating walking stick insects at Children’s Zoo to the 12-foot-long eastern black rhinos, animals all over the zoo benefit from its plants. Yet the zoo gardens must be lovely for people, too—which makes it so handy that tortoises go nuts for beautiful hibiscus blooms

By Beth Botts