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The New Book of Knowledge

National Zoo zookeeper
Bai Yun, a panda who lives at the San Diego Zoo, gave birth to a cub, seen in the yellow square, on August 2, 2005.
(Photo: Zoological Society of San Diego)

Keeping wild animals in zoos, or zoological gardens, is an old practice. But today zoos seem more popular than ever. Each year more people in North America go to zoos than to all the professional baseball, football, and basketball games combined.

Why are zoos so popular? One reason may be that more people now live in cities and towns, where they see little wildlife. They seek places where they can have some contact with nature. And perhaps people sense that when they visit a zoo, they have the opportunity to see things they have never seen before. In many zoos, you can see more kinds of animals in a day than you might see in weeks of travel to faraway places.

Zoos do much more than provide recreation, however. They teach people about the importance of nature. They provide scientists with opportunities to study wild animals. And they are also important because thousands of species of wild animals are in danger of dying out. Saving these endangered species is one of the purposes of modern zoos.

Zoo Exhibits

Traditional zoo exhibits include mammals, birds, reptiles, and amphibians from all over the world. The animals may be grouped according to type--a building for monkeys or reptiles, for example. Animals that have special climate needs, such as tropical species, are especially likely to be housed together. Some zoos group their exhibits according to the continents or geographic regions of the earth. This is called zoogeographic exhibition.

Years ago, most zoo animals were displayed in cages or in areas enclosed with high metal fences. Today, however, many zoos display their animals in more natural surroundings. They are also branching out to include new kinds of exhibits.

Natural Habitat Exhibits.

 These exhibits show animals in settings that mimic their natural homes. For example, a zoo may feature an African grasslands exhibit, in which zebras, giraffes, antelopes, and ostriches roam about in open spaces with grass, a water hole, and perhaps some trees. Some zoos have built tropical forest exhibits for monkeys and other tree-dwelling animals. Ducks, turtles, beavers, and otters may be shown in a wetlands exhibit that contains a pond or a marsh. In many zoos, you can visit polar ice caps, blistering deserts, and steamy jungles—all in a day.

In these exhibits, zoos use glass panels, moats, or thin steel wire to keep people out and animals in. Sometimes there is no barrier between people and the animals. For example, many zoos have walk-through aviaries, where visitors walk on pathways or boardwalks while dozens of birds fly around them.

The animals are more comfortable in these surroundings, and thus they are more likely to remain healthy and reproduce. Natural exhibits also help zoo visitors learn about the animals and understand how important their wild habitats are to their survival.

Special Exhibits.

 Children's zoos, with special exhibits for young people, have been popular parts of big zoos for many years. Today some zoos are teaching children about animals by letting them do some of the things animals do. At the Bronx Zoo in New York City, for example, children can imitate burrowing prairie dogs by wriggling through underground tubes and tunnels. Many other zoos have similar participatory exhibits.

Animal rides are another popular attraction at zoos. Horse, pony, camel, and even elephant rides bring zoo visitors into close contact with animals. Many zoos also offer shows and demonstrations featuring live animals—sea lions, elephants, and sometimes even birds of prey such as hawks and eagles.

Nocturnal displays are featured at some zoos. Many animals are nocturnal—that is, they are active at night and sleep during the day. In the past, zoo visitors rarely saw these animals moving around. Now some zoos are using special lights to reverse the animals' sleeping patterns. Bright lights are kept on at night, so that the animals sleep. In daytime, the exhibit is lit by red light that the animals can barely detect. The animals behave as if it were night, and zoo visitors can see them.

Zoos are also showing more kinds of animals. Many zoos now include insects, spiders, crustaceans (lobsters, for example), and other invertebrates (animals without backbones) in their exhibits. And some display fish and other marine animals, which traditionally had been exhibited only in aquariums.

A few zoos have developed exhibits that include features of museums. An example is the Louisiana Swamp exhibit at the Audubon Park Zoo in New Orleans, Louisiana. In addition to displaying swamp animals in their natural habitat, it shows how early settlers lived and interacted with the wildlife.

How Zoos Acquire Animals

Years ago, it was common for zoos to buy animals that had been captured in the wild. The zoos usually worked with animal dealers, who would supply certain kinds of wild animals. But as wild animals have become rarer, zoos have begun to breed as many animals as possible. Zoo officials realize that collecting too many animals can harm wild species. Today, zoos usually acquire animals by breeding or borrowing them from other zoos.


 Breeding wild animals can be difficult. Some kinds of animals, such as wild sheep and even tigers, breed readily in zoos. But others require special attention. Monkeys and apes, for example, often have strong preferences for mates of the right appearance and personality. Sometimes female monkeys need to observe breeding and infant care when they are young, so that they can behave naturally as mates and parents when they become adults.

Zoos often study the natural habits of animals to breed them successfully. For example, research has helped zoos breed cheetahs, which are slender, graceful spotted cats from Africa. Zoos previously kept male and female cheetahs in pairs for years without breeding taking place. But scientists studied cheetah behavior and learned that females need to come in contact with several males during the breeding season. Males, it seems, are also more successful breeders if they have to compete to mate with a female.


 When zoos are successful in breeding animals, they often sell animals to other zoos or exchange them with one another. Animal exchanges have become one of the most common ways that zoos acquire animals. Every year thousands of animals, such as snow leopards, antelopes, penguins, and monkeys, are exchanged. Loans between zoos for breeding purposes are another way in which zoos obtain animals. These loans are important because they permit zoos to find unrelated animals for mating.

Breeding, exchanges, and loans demonstrate one of the ways that zoos take part in wildlife conservation. These activities can make collecting wild animals unnecessary. And exhibiting rare animals that have been bred in captivity helps make visitors aware of the problems facing wildlife and the role of zoos in conservation.

Keeping Animals Healthy

Perhaps the most important part of a curator's job is to keep the zoo animals healthy and to prevent disease and injury. This involves making sure that the animals are properly fed and that they receive good veterinary and other care.

Animal Diets.

 More kinds of food are probably served in a zoo than in most restaurants. To feed their livestock, zoos are always buying large quantities of grain, fruit, vegetables, meat, fish, and other foods. Many zoo visitors enjoy seeing animals fed. Zoos often announce the feeding times for such animals as big cats, sea lions, eagles, and crocodiles because these animals are fed on regular schedules. For most birds and small mammals, food is available at all times.

Many zoo animals, especially those that eat a wide variety of foods in nature, are fairly easy to feed in captivity because they thrive on a diet that is easy to obtain. Raccoons, for example, eat familiar foods such as apples, carrots, grapes, bananas, hard-boiled eggs, and fish, as well as commercial livestock feed.

Some animals are picky eaters in nature and need special diets. A famous example is Australia's koala, which eats only fresh leaves of eucalyptus trees from its native land. Giant anteaters from South America eat mainly termites and ants in the wild. In zoos, they eat a special mixture that includes water, evaporated milk, ground horsemeat, cereal, and raw egg yolks.

Some animals eat their food just as it comes. But for many animals, food must be measured, chopped, combined, or even cooked. One example is the diet of the giant panda, which in the wild eats mainly bamboo. Zookeepers provide bamboo, apples, carrots, ground beef, and a special food called panda bread. This is made of corn meal, soybean meal, bone meal, salt, and water. The ingredients are mixed, patted into a cake pan, and baked.

Baby animals sometimes have special dietary needs. Baby mammals do best if they nurse from their mothers, but sometimes an infant may not nurse properly or a mother may not produce enough milk. Then the zoo must assign a keeper to bottle-feed the baby. Baby birds can pose problems, too. Sometimes the strongest chick in the nest takes most of the food, so zookeepers must feed the others by hand to make sure that all receive enough food.

Diet plays an important part in keeping animals healthy, and zoo diets are constantly being improved as scientists learn more about the nutritional needs of animals in zoos. Zoos must know a great deal about the nutritional content of the food they buy. They often add vitamin and mineral supplements to the food to prevent the problems that can arise if these substances are lacking.

Veterinary Care.

 Years ago, most veterinary treatments for zoo animals were based on knowledge of dogs, cats, and other domestic animals. Today research is advancing knowledge of wild animal medicine all the time.

Most big zoos have a full-time staff of animal health professionals, including veterinarians and animal health technicians. These people examine the animals and treat any health problems that arise. Some small zoos use local veterinarians to help with animal health problems. But even when a zoo has a full-time veterinarian, it may occasionally need the assistance of a specialist, such as a veterinary dentist, bacteriologist, or surgeon.

Even in zoos with the best animal health programs, animals occasionally get hurt and need emergency treatment. In these cases, it is often necessary to restrain the animal--wild animals do not sit still for the veterinarian. If the animal cannot be held still, the veterinarian uses a tranquilizing drug or even a general anesthetic. This can be risky because the proper doses for different sizes and species of animals are not always known.

Other Care.

 Many aspects of animal care contribute to keeping animals healthy. The animal curators (managers), veterinarians, and other zoo professionals work together to design ways to prevent illness and injury.

One of the regular jobs of animal keepers is to clean the places used by animals and those where food is prepared. Good sanitation practices can prevent diseases caused by bacteria and parasitic organisms.

Zoo professionals prefer to handle their animals as little as possible because, for many animals, handling causes stress. Stress can make a healthy animal sick and a sick animal worse.

Research and Education

Research and education are important goals of the modern zoo, although many zoo visitors are not aware of these activities.


 Zoo research usually falls into three categories: breeding biology, veterinary medicine, and nutrition. Research into breeding biology is important to conservation, especially in efforts to breed endangered species. For example, the San Diego Zoo, the Cincinnati Zoo, and others are developing better ways to diagnose pregnancy in wild animals. Research into veterinary care and nutrition is essential to improving wild animal care. At the Bronx Zoo, for example, a professional nutritionist has conducted studies that have helped the zoo formulate better diets for leaf-eating monkeys. At some zoos, research into animal behavior is also becoming common, as curators seek to understand how animals use natural habitat exhibits.


 Most zoos have education departments that conduct group programs. An educator or naturalist may demonstrate live animals, point out important aspects at exhibits, and present brief talks illustrated with slides, films, or videotapes. Many North American zoos also offer summer day-camp programs for children, special lectures for adults, and workshops for teachers.


Throughout history, people have had various reasons for keeping collections of wild animals. In ancient times, rulers kept wild animals to show off their wealth, entertain their subjects, or present as gifts to other kings and queens. The first step toward the modern zoo may have been taken 3,000 years ago, when a Chinese emperor developed a collection of animals for study rather than amusement.

There were public zoos in Europe as early as the AD 900's, but they were mostly small. In the 1700's, however, zoos expanded their collections and began to be involved in research. The first U.S. zoos were founded in the mid- and late 1800's, in cities such as Philadelphia, New York, and Chicago. The National Zoological Park, in Washington, D.C., was set up by Congress in 1889.

In recent years the goals of conservation, education, and research have become more important to zoos. This has led to many changes in the way zoos work and in their appearance.

Douglas Falk
Assistant Curator of Education, New York Zoological Society