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January/February 2009 Smithsonian Zoogoer cover
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Mixing It Up

Enrichment offers animals variety and stimulation in their daily lives.

by Linda Lombardi

It’s morning at the Smithsonian National Zoo’s sloth bear exhibit, and keeper Jenny Spotten arrives with an armload of shoeboxes. She sets them down and begins to fill a shoebox with mulch. Then she mixes in a handful of food—some fruit, nuts, special bear chow—and closes the shoebox lid. She places the box in a certain spot within the exhibit, then puts a log on top of it. She proceeds to climb around the entire exhibit, tucking food into decaying branches, nooks in rock walls, and mulch pits.

Why is Spotten going to all this effort? Because she’s offering the four sloth bears more than just breakfast—she’s providing them “enrichment” to stimulate their bodies and their minds. “I could dump a bucket of food in one place, but then five minutes later, the bears would have nothing to do,” she explains. Instead, the bears are given the opportunity to search and forage for their food, similar to the way they might in the wild.

Sloth bear honey treat

Keeper Jenny Spotten makes a sweet enrichment treat for the sloth bears. (Mehgan Murphy/NZP)

Enrichment is central to what zookeepers do each day to keep animals active and engaged. It includes the wide variety of activities and objects that keepers offer to present mental and physical challenges to the animals.

The goal is to encourage natural behavior and give animals options—getting them to use their senses, exercise their bodies, and interact socially in species-appropriate ways. Heidi Hellmuth, the National Zoo’s curator of enrichment and training, says that keepers have historically offered zoo animals enriching activities, but a well-defined idea of enrichment didn’t really take off until the 1990s. Now, the Association of Zoos and Aquariums requires accredited institutions like the National Zoo to include enrichment in their basic standards. “Now we understand that it’s not a separate part but an integral aspect of animal care,” she says.

Hellmuth is working on formalizing enrichment goals for every species at the National Zoo, and she says that what’s particularly significant is that the goals will include categories of behaviors to encourage. These include sensory, social, and cognitive behaviors, as well as methods to elicit them, such as the use of objects and the design and furnishing of exhibits. Keepers will have the freedom to decide how to get animals to perform desired behaviors, such as foraging. “It’s an approach that we haven’t heard of any other zoo taking,” she says. “We’re hoping to raise the bar.”

One category that’s particularly multifaceted is dietary enrichment, as with the sloth bears. Mealtime is when many daily enrichment activities take place, for obvious reasons. Not only is much natural behavior related to seeking food, but animals have to eat anyway, so why not multitask? The most basic dietary enrichment involves varying certain elements of the actual diet—apples one day, bananas the next. But food can also be used to present cognitive and physical challenges; for example, the sloth bear has to figure out where the food is and then dig it out, encouraging a variety of natural behaviors.

Sloth bear foraging
The Zoo's sloth bears get exercise and use their natural instincts to find hidden food. (Mehgan Murphy/NZP)

Of course, in the wild a bear would more likely be tearing bark off of branches than cardboard off a box. Since it’s impractical to provide an endless supply of trees, creative artificial alternatives can serve the same purpose. You’ll see this all over the Zoo: an octopus searching for a piece of shrimp in a plastic puzzle, marmosets digging for mealworms that have burrowed among the strings of a mop, great apes searching for treats through bags and in plastic toys.

Dietary enrichment often keeps things more interesting for the keepers as well as the animals. At the Zoo’s Bird House, keeper Mario Reyes cuts the top off an apple, digs it out like a jack-o-lantern, and fills it with mealworms or waxworms. He’ll freeze treats inside of ice cubes, and cut slits in a whole banana to insert nuts for parrots or half-frozen newborn mice for magpies. They’re combinations that you’d never see in the wild, but like the bear’s shoebox, they have the desired effect when the birds are looking for food, he says: “They have to work at getting it out.”

Beyond meal-based enrichment, a similar type of enrichment can be done to stimulate the animals’ senses. One of the Zoo’s tigers, Rokan, exercises his keen sense of smell one morning as he checks out his yard. Keeper Kristen Clark has sprayed catnip in various spots in the yard. She’s also spread around droppings from zebras and gazelles (readily available materials at the Zoo), which are similar to the tiger’s prey in the wild.

At an especially delectable spot, Rokan stops and stands with his mouth hanging open—a pose you may have seen in house cats. This behavior, called the flehmen reaction, displays Rokan’s use of what’s called a Jacobson’s organ in the roof of his mouth in order to take in a smell. Clark explains: “By making that face, he’s moving the scent across that organ.”

Tiger enjoying "bloodsicle"
A "bloodsicle" provided by keepers excites the tiger's senses. (Mehgan Murphy/NZP)

Sometimes food isn’t all that matters. Many animals must have companions to hang out with in order to be healthy—they need social enrichment. Zoos were once much like stamp collections; the goal was to have one each of a large variety of species. Now it is recognized that some animals have to live in social groups, like families, for their own well-being. Zoos today tend to keep fewer species, to make room for more individuals of each species.

Social life often means getting out and meeting new folks. The cheetahs, for example, are frequently moved to different enclosures where they can see different cats in the adjacent yards. This kind of social enrichment can also be valuable for species like the giant panda that are usually considered to be fairly solitary, says giant panda curator Lisa Stevens. “We’ve discovered here that we can house our adults together,” she says. While giant pandas are not known to pursue social interactions in the wild, Stevens points out that scientists don’t have enough evidence of what actually happens in the animals’ natural environment. “The play sessions are quiet, it’s a dense understory, and what’s the likelihood that someone has seen it? The field research hasn’t been done,” she says.

Just as people want to have a say in their social interactions, an important part of any kind of enrichment is giving animals choices and some control over how they spend their time. Giving the pandas the opportunity to interact does exactly that, says Stevens: “It gives them another choice. Even if they only play together for a couple of minutes, it’s a choice they’ve made.” Choice is important because otherwise, she says, “we take away the unpredictable aspect of their life in the wild.” Because novelty and choice are important to enrichment, keepers maintain logs to make sure that enrichment items like scents and objects are varied each day.

But enrichment isn’t only about things that change: it starts with the animal’s basic living space. A good animal exhibit is one that meets many enrichment goals at once. There’s a reason that zoos have replaced old-fashioned bare cages with complex naturalistic exhibits, and it’s not just for the aesthetics. The different pools and streams for the otters at Asia Trail, for example, beautify the exhibit, but they also give the animals a choice of water that’s deep or shallow, heated or unheated. And the otters clearly think that the plantings are more than decoration. “You’ll see them running around with big tufts of plants in their mouths,” says curator Tony Barthel.

An enriching exhibit offers the animals opportunities to perform their natural behaviors. At the Bird House, the brush is intentionally left to grow dense in the cassowary yard. This encourages the large bird to use its casque, the bony structure on its head, to push through the foliage like it would in the wild. And in a building like the Small Mammal House, every branch, vine, and stone in an enclosure was placed there by a keeper who was thinking about the animals’ behavioral needs.

“An animal-appropriate environment promotes healthy behavior,” says Stephen Schulze at the Zoo’s Small Mammal House, where exhibits are designed to encourage natural food-gathering and social behavior. An exhibit for small, arboreal tree shrews, he points out, includes plenty of skinny branches for climbing—and they’re designed to have a little bit of give, like real trees, instead of being immobile. Chunky mulch not only resembles the forest floor visually, but allows mealworms to burrow down into it, where shrews can forage for them. And in a nearby enclosure, the meerkats’ rocky exhibit features hilly areas so that the animals can carry out their instinctive guarding behavior. “The idea of providing different heights satisfies their group behavior of posting someone who’s on guard,” Schulze says, pointing to the animal sitting on its haunches, looking around.

Enrichment means not only paying attention to how an exhibit suits a particular species, but how it caters to an individual animal as well. For one aged, blind coati at Small Mammals, Schulze says he keeps the exhibit stable and safe, without the novelty and stimulation a younger animal would require. At the Bird House, one parrot is reluctant to fly, so the keepers have had to take special steps to encourage it. “We put stuff in to make him have to fly if he wants it,” says keeper Gwen Cooper. They’ve also modified the exhibit so the perches aren’t all connected: “Now he has to at least fly from one perch to the other.”

These solutions may seem obvious, but not all behavioral needs are clear, even to the Zoo’s animal experts. Biologist David Kessler cites one instance in which the Small Mammal team was trying to figure what to do to get a rock hyrax to move around more. They had to do some research into the published literature and found that hyraxes in the wild stay still most of the time. “So the hyrax was actually doing just fine,” says Kessler.

In some cases, the Zoo’s keepers and curators do research of their own to determine the animals’ enrichment needs. When the Invertebrate Exhibit acquired five baby cuttlefish, museum specialist Tamie DeWitt and her colleagues wanted to learn more about them. DeWitt started by making a list of some of their known and observed behaviors. This list included not only swimming, resting, and waving their arms, but also changing the colors and patterns on their skin—something not many other creatures can do.

Cuttlefish eating shrimp

Wiggling a shrimp brings out a cuttlefish's natural behaviors, including changing color. (Mehgan Murphy/NZP)

“They’re highly visual,” she says. “We’ll try changing backdrops—will stripes make them do stripes?” She watches as a volunteer, her arm submerged in water, patiently offers a piece of shrimp on the end of a fishing line to a cuttlefish with a square white patch on its back. As she wiggles the shrimp, the white patch goes dark for a moment. A light square with three stripes radiating from it appears and flashes on and off, and then the pattern settles down to the original white patch again.

This sort of experiment helps DeWitt, invertebrate curator Alan Peters, and Hellmuth figure out how cuttlefish behave in order to test out new enrichment strategies and track their reactions. These research efforts are needed because there’s no textbook on how to enrich a cuttlefish.

Whenever Zoo staff come up with new enrichment ideas for the different animals, frequent follow-up testing and evaluation of the methods is essential. You can’t always predict what will happen when an enrichment item meets an animal. In one example, a hard, thick plastic ball was considered a good product to use to stimulate some of the animals to play. “The manufacturer of the ball used to call it ‘the indestructible ball’ until someone gave it to a lion,” says curator Hellmuth. “Now they call it ‘the almost-indestructible ball.’”

Lion toys run ragged

Heidi Hellmuth, the Zoo's curator of enrichment and training, displays "almost-indestructible balls" punctured by lions. (Jessie Cohen/NZP)

The balls can usually be used for a couple of years, according to keeper Clark, but they won’t stand up to a big cat indefinitely. A retired ball that she hauls out of a storage space is raked with claw marks and has a ragged-edged hole in it. “We have to take the ball away,” explains Clark. “A lion could get a tooth stuck if it tried to carry the ball in its mouth.”

But despite occasional glitches, enrichment is more useful than troublesome. It can be used to solve specific behavior problems. Reyes at the Bird House says that adding different juices to the nectar fed to honey-eaters means it’s easier to give them medication in their food, because they’re used to new flavors. In another example, a red ruffed lemur named Ceres at the Small Mammal House lost her mate, Nike, so she stopped eating and was losing a dangerous amount of weight. Until a new mate could arrive, keepers employed many enrichment methods to meet her social needs: Ceres was housed with other animals, had a stuffed animal that she groomed and slept with, and got extra attention from the keepers. She also had a TV that played videos of nature programs. Ceres not only started eating and gaining weight, says keeper Rebecca Smithson, but she responded to the enrichment activities in other ways as well. She would react to the TV programs, showing that the stimulus succeeded. “When lemurs vocalized, she vocalized back,” says Smithson. “She hadn’t vocalized since Nike died.”

Whatever the activity, it all comes back to ensuring a high quality of life for the animals at the Zoo. To do this, keepers look at things from the animal’s point of view. Keeper Spotten watches a sloth bear rip into a shoebox of hidden food and smiles with obvious affection. “Their natural instinct is to go around and destroy stuff,” she says. “It’s just way more fun for a bear to do that than to pick up nuts off the ground and eat them.”

— Linda Lombardi is a freelance writer who has worked as an animal keeper at the Smithsonian’s National Zoo.


Look for a Sign

New signs all around the Zoo invite visitors to learn more about enrichment. If you see a WHAT'S THAT? sign near an animal exhibit, you can call the posted phone number and hear a recording of a keeper explaining a specific enrichment activity. Get fascinating inside info on how the antelopes act around log piles, why the toucan needs a training crate, and more. Also, check out animal enrichment photos from the Zoo.