Animal freeze

The zoo is actually two separate facilities. The San Diego Zoo in Balboa Park — the largest urban park in the country and the site used by Orson Welles to film the Xanadu scenes in "Citizen Kane" — is near downtown. It offers 800 animal species (4,000 specimens) and 6,000 plant species on 100 acres. The 1,800-acre Wild Animal Park, 30 miles north of San Diego in San Pasqual Valley near Escondido, offers 3,500 representatives of 429 animal species and 3,500 plant species.

The whole thing started in 1916 when the Zoological Society of San Diego founded the San Diego Zoo to care for the animals brought in for the Panama-California International Exposition. The Wild Animal Park was established in the 1960s as a protected natural habitat to serve as a breeding ground. Almost as an afterthought, the public was first admitted in 1972.

Both the San Diego Zoo and the Wild Animal Park are private, nonprofit facilities operated by the Zoological Society of San Diego. That's the same organization that helps to run the Keauhou Bird Conservation Center on the Big Island and the Maui Bird Conservation Center, recently in the news when possibly the last remaining po'ouli bird succumbed to avian malaria. Both centers have had great success with the 'alala, or Hawaiian crow, the nene goose and the reintroduction of the palila to the slopes of Mauna Kea.

As one can tell from its activities, the Zoological Society of San Diego, with an annual operating budget of $150 million garnered entirely from contributions, memberships and 3.2 million visitors each year, is devoted to the worldwide preservation and propagation of species. For example, uninhibited by city budgets or politicians, the zoological society in 1996 rented two giant pandas at $1 million a year from China. Since then, in spacious and nearly natural habitats, the pandas have reproduced. This year one of the grown-up offspring, Hua Mei, was sent to China, where she promptly mated then gave birth to twins. (Fifty percent of panda births are to twins, one of which is normally abandoned by the mother. The zoological society has developed ways to save both offspring.)

The zoological society also maintains a "frozen zoo," collections of DNA from endangered species. While at the zoo, you can visit a cloned wild ox, the Javan banteng, created two years ago from cells frozen 20 years ago.

Helping to ensure the long-term viability of captive and wild populations entails educating the public, and that's where you and the two parks enter the picture. The zoological society provides us not only a grand view of biodiversity but the opportunity to connect with wildlife. In fact, the San Diego Zoo and Wild Animal Park offer perhaps your greatest opportunity to marvel at two (animals and plants) of the five kingdoms that comprise life on earth. (The other three are fungi; protista or single-cell organisms; and monera or single-cell bacteria.)

Skyfari above zoo

Karen, a female orangutan at the zoo's Absolutely Apes exhibit, is taunted by two siamangs who share the habitat. San Diego Zoo photos

When you enter, be sure to get a map and head immediately for the nearby guided bus tour loading area. A 40-minute excursion, complete with expert narration, will take you by many of the main habitats. On the way, you can familiarize yourself with the zoo's layout and the locations of the areas you want to visit on foot. Following the bus tour, hop on the aerial tram ride from Skyfari East. It will give you a bird's-eye view as you get your bearings. Once you complete the Skyfari round trip, it is time to walk the zoo.

A recommended route is to cross the road from Skyfari East to the Reptile House and begin from there. Or, you can visit the nearby Children's Zoo and then visit the Reptile House. The rest of your day should be spent trekking the lush canyons and mesas of the zoo. Along the way, you can hop on and off an express bus that makes designated stops.

Going ape

A cheetah at the San Diego Zoo's Wild Animal Park looks over the East African plains exhibit, a 90-acre habitat that's home to giraffes, rhinos, wildebeest and more. San Diego Zoo photos

Right after Flamingo Lagoon, head west for the primate habitat called Absolutely Apes. Featured are great and lesser apes from Indonesia, orangutans and siamangs respectively. The orangutan is the only great ape from Asia, and the other three species (gorilla, chimpanzee and bonobo) are from Africa.

The exhibit marks the first time that orangutans and siamangs, two different species, have lived together in one setting at the zoo. Surprisingly, the siamangs, the largest of all lesser apes, fit right into and even dominate the social structure. Their bellows and hoots to establish territory can be heard throughout the zoo.

From Absolutely Apes walk downhill to Gorilla Tropics. This is home to two troops of western lowland gorillas, a subspecies of gorilla that is slaughtered for meat in the Congo. Each troop has a dominant male, a silverback with a nearly white saddle covering its rump and thighs. Waterfalls within this tropical habitat drown out the sounds of humans passing by and leave these magnificent animals undisturbed.

From Gorilla Tropics you can make your way to the Scripps Aviary, a habitat for hundreds of birds. Epidemiologists have noted the first human transmissions of a deadly strain of avian flu in Thailand and China as well as exotic Newcastle disease from fighting gamecocks and the West Nile virus from mosquitoes. The zoological society has begun a vaccination program of flamingoes, condors and other species to ward off the West Nile virus, and the many species of birds are watched carefully to protect them and you.

From the aviary, walk to the bonobo or pygmy chimpanzee habitat to visit another species of great ape. The bonobo (kingdom animalia, phylum chordata, subphylum vertebrata, class mammalia, order primates, family pongidae, genus gorilla, and species Pan paniscus) is said to be the species closest to humans (order primates, family hominidae, genus homo, species sapiens). About 98 percent of human and bonobo DNA sequences are identical. (Not to worry. Scientists are discovering that the proteins produced by the identical genes are significantly different and that the proteins are what differentiate the two species.)

When you leave the bonobos, it's probably a good time to pause at the nearby Treehouse. There you will find fast-food service as well as full-service dining at Albert's Restaurant, named after one of the zoo's great apes. You can eat inside or on the outside deck while soothed by the sound from a nearby waterfall.

Pandas, polars and pigs

Among the tigers who live at the zoo's Tiger River is a reputed man-eater rescued from the wild. San Diego Zoo photos

As you approach the end of the Tiger River path, pause at the hippopotamus amphibious habitat with its 150,000-gallon pool. The baby hippo born at the zoo is kept away from the territorial male. In fact, the females pull away from the pod before giving birth so as to avoid contact with the males. Hippos, which love to lollygag around in the water and sun, have sensitive skin and secrete a fluid that seems to serve as an antibiotic and sunblock in one.

When you emerge from Ituri Forest, turn right and head down Panda Canyon. Don't be surprised if the giant pandas from China are asleep in the trees when you arrive. Because their evolution includes an adaptation to a one-staple diet, bamboo, they lack the nutrition needed for energy. Asleep or not, the panda cub Mei Sheng (for "Born in the USA") will charm you. The San Diego Zoo is the only U.S. zoo to breed, birth and rear healthy cubs.

From Panda Canyon, catch the express bus to the Polar Bear Plunge. This is a 2.2-acre tundra habitat dominated by a 130,000- gallon, 12-foot-deep pool of water chilled to 55 degrees. The two young occupants were rescued in Alaska when a hunter shot the mother. Visitors can watch the polar bears from an underwater viewing area.

From the Polar Bear Plunge you can start the long walk through the Horn & Hoof Mesa, featuring zebras, gazelles, giraffes, bongos, and pigs, including a rare Chacoan peccary from Paraguay and Visayan warty pigs from the Philippines.

At the end of the Horn & Hoof Mesa, walk down Cat Canyon and then take Kiwi Trail up to Elephant Mesa. Among other animals, you'll see some magnificent rhinos. From Elephant Mesa, head for Bear Canyon but stop first at the Bat Exhibit and then at the Koala Exhibit. The koalas, marsupials that live on a diet of eucalyptus leaves, have evolved a unique digestive system that enables them to use the few nutrients offered by eucalyptus and at the same time to decontaminate the poison in the leaves. At the koala habitat you'll encounter also a rare tree kangaroo.

As you near the bottom of Bear Canyon, turn left and walk through Fern Canyon and back to the main entrance. Before you leave the zoo, stop at the gift shop where you'll find some interesting items. You might also take the opportunity to pick up the latest edition of Zoonooz, the zoological society's monthly publication that combines scholarship with entertainment. Even better, you can help the cause of preservation by joining forces with the 250,000 members of the zoological society. Your membership ($79 for out-of-region Zip codes) provides you with a subscription to Zoonooz and free admission for a year to the zoo and to Wild Animal Park.

Wild Animal Park

A giant panda, Bai Yun, cuddles with her newest cub, Mei Sheng, at the SBC Giant Panda Research Station at the San Diego Zoo. San Diego Zoo photos

The zoological society's Center for Conservation and Research for Endangered Species is at Wild Animal Park. CRES features an advanced and computerized library (11,000 books and 635 serial titles) and four different labs. At CRES, scientists including Dr. Fred Bercovitch, an expert in primate physiology and genetics, explore ways to put findings from evolutionary and behavioral biology to work for conservation and propagation. (Dr. Edward O. Wilson, the father of behavioral biology and author of the breakthrough work of 1975, "Sociobiology: The New Synthesis," was the zoological society's 1998 Conservation Medalist.)

The Wild Animal Park, because it started as a preserve not open to the public with human visitors an afterthought, is a little more difficult to see than the zoo. It is first and foremost an accredited botanical garden and protected conservation site. Among other things, many of the deadly California rattlesnakes you saw at the San Diego Zoo make the Wild Animal Park their natural home, so stay on designated trails.

The best place to start is Nairobi Village. It serves as a sort of hub to the various paths and excursions. While at the village, be sure to walk through Lorikeet Landing. This aviary features multicolored parrots from Australia that aren't shy about using you as a landing spot.

Bush Line Railway

A southern white rhino grazes alongside sable antelope at the Wild Animal Park where you can travel by monorail or ground safari tour. San Diego Zoo photos

Ride the monorail first thing because it can get crowded later in the day. It travels through four separate 80-acre areas: East Africa, South Africa, Asian plains and a Eurasian water hole. You'll encounter lots of groups — herds of elephants, towers of giraffes and crashes of rhinos, including white rhinos that once numbered only 50 in the world but now are at 12,000.

Look also for the one-year-old elephant calf. The park rescued its mother and five other African elephants in 2002, in spite of protests and even lawsuits by PETA, the animal-rights group, when Swaziland embarked on a culling program. Six months later — the average gestation period for African elephants is 21 months — the rescued mother gave birth to Vus'musi, which means "to build a family."

If you want to transverse the same four 80-acre areas in an open-air truck, special photo caravans are available at a cost of $90 for the 2-hour trip. Don't be alarmed if a rhinoceros lumbers alongside your truck to size you up.

Heart of Africa

At San Diego's Wild Animal Park, guests in a caravan safari tour have an opportunity to hand-feed giraffes. San Diego Zoo photos

Along the way you'll encounter okapis, cheetahs and monkeys. You'll see giraffes you can hand- feed. Be sure to see also the critically endangered black rhinos, including a mother and baby. Whenever a zookeeper approaches this habitat, the mother reins in the baby and then charges in the direction of the intruder.

The horticulture in the Heart of Africa is remarkable. You'll even see papyrus, the plant that gave us our word for paper because the ancient Egyptians pressed, dried and wrote on it.

Also of great interest are the yellow bark acacia or fever trees, once thought to cause malaria because they are common in watery areas where mosquitoes breed, and the fortnight lily, which blooms every two weeks for just one day.

This savanna habitat features six young lions. There are 36 species of the cat family (felidae), but lions (Panthera leo) are the only truly sociable species. The females in the pride share a traditional home range and remain lifelong residents of their mothers' territories, but adolescent males are forced to depart when their fathers begin to see them as rivals.

Condor Ridge

Wild Animal Park is devoted to Asian and African species with the exception of Condor Ridge, which is reserved for native Californians.

Featured are the California condors that dine exclusively on carrion. If you're lucky, you'll see one of these birds flaunt its 9-foot or greater wingspan that allows the condor to soar on the air currents without so much as flap of the wings. There were only 22 of these magnificent birds left in 1980, but Wild Animal Park's breeding and release program has restored the population in the wild to 100 or more.

On the walk up Condor Ridge you'll see American magpies, greater roadrunners, the birds that eschew flight to race around on the ground in search of small animals to eat, and western Harris' hawks. These hawks, unlike most, hunt in cooperative pairs or groups.