|Location||Denver, Colorado, USA|
|Land area||80 acres (32 ha)|
|Number of animals||3,699 (2010)|
|Number of species||641 (2010)|
|Annual visitors||1.6 million (2001–2010 average)|
|Major exhibits||Predator Ridge, North Shores, Tropical Discovery, Elephant Passage, Primate Panorama, Bear Mountain|
The Denver Zoo is an 80-acre (32 ha) facility located in City Park of Denver, Colorado, USA. Founded in 1896, it is owned by the City and County of Denver and funded in part by the Scientific and Cultural Facilities District (SCFD). It was the most popular paid attraction in the Denver metropolitan area in 2005.
The Denver zoo was started with the donation of an orphaned American black bear. With the construction of Bear Mountain, it became the first zoo in the United States to use naturalistic zoo enclosures rather than cages with bars. It expanded on this concept with Primate Panorama with its huge mesh tents and open areas for apes and monkeys, and Predator Ridge, which has three separate areas through which animals are rotated so that their overlapping scents provide environmental enrichment. Toyota Elephant Passage (which opened on June 1, 2012) is divided into five areas for rotating the various species.
The Denver zoo is accredited by the (American) Association of Zoos and Aquariums (AZA) and is also a member of the World Association of Zoos and Aquariums (WAZA). In 2009, the zoo achieved ISO 14001 certification.
Early years 
The Denver zoo was founded in 1896 when an orphaned American black bear cub named Billy Bryan – short for William Jennings Bryan after the contemporary American politician – was given to Thomas S. McMurry (mayor of Denver from 1895–1899) as a gift. McMurry gave the hard-to-manage cub to the keeper of City Park, Alexander J. Graham, who started the zoo with this animal. Other animals at the young zoo included native waterfowl at Duck Lake, native prairie dogs and antelope which roamed the park, and a flock of Chinese pheasants, which later populated the eastern plains of the state.
In 1905, a population of red squirrels was added to the zoo's collection; this population grew rapidly and decimated the bird population at Duck Lake. A plan to shoot the squirrels was scrapped when citizens protested. Instead, as many squirrels as could be caught were sent to the Denver Mountain Parks.
Mid-20th century 
The zoo was a motley menagerie until 1906, when Mayor Robert W. Speer declared that the zoo's "[p]rison bars can be done away with" in favor of "concrete rocks, waterfalls, trees, etc." Speer hired the city's landscape architect, Saco R. DeBoer, to draw up the plans for his renovation and appointed Victor H. Borcherdt as zoo director.
Borcherdt designed the Bear Mountain exhibit, which opened in 1918. This structure is 43 ft (13 m) tall and 185 ft (56 m) long, and cost $50,000 to build. It was built of dyed and textured concrete forms cast from Dinosaur Mountain just outside of Morrison, Colorado. Hidden moats replaced cage bars, and native plants and an artificial stream enhanced the natural look. The two main exhibits originally housed polar bears and grizzly bears. The south tip of the exhibit was designed to resemble Mesa Verde National Park. Originally it housed monkeys, but due to escape problems sea lions were housed there instead. Between 1941 and 1961 it housed a female polar bear named Velox, who became the mascot of the 31st U.S. Infantry Regiment in 1952. Velox died at the zoo in 1961 and is buried at the zoo. Bear Mountain established Denver as one of the foremost among American zoos, and the Saint Louis Zoo hired Borcherdt after seeing the exhibit.
Although other zoos in the region made extensive use of New Deal funds to upgrade their facilities, only one notable addition was made to the Denver Zoo between 1918 and 1950. Monkey Island was built in 1937 using funds from the Works Progress Administration. Mayor Benjamin F. Stapleton funded the zoo very little, and it was in poorly maintained condition when Mayor Quigg Newton was elected in 1947. Newton hired DeBoer, the architect involved with the zoo's design forty years before, to plan a rebirth. Starting with the 1950 overhaul of Monkey Island, the zoo has steadily added to and improved its exhibits.
The Denver Zoological Foundation was created in 1950, the same year that the zoo acquired its first elephant, Cookie. A Children's zoo was opened in 1951 (since replaced by Primate Panorama). A perimeter fence was built in 1957, defining the zoo as a separate area but still within City Park. Automobile traffic in the zoo was finally eliminated completely in 1959. Pachyderm Habitat was opened the same year, and Cookie was joined by a second elephant, Candy.
The zoo opened the Feline House in 1964, a Giraffe House in 1966, and an Animal Hospital in 1969. Bird World was opened in 1975, followed by the Mountain Sheep habitat in 1979, Northern Shores for polar bears, otters, and pinnipeds in 1987, and Wolf Pack Woods in 1988.
The Marine Mammal Protection Act of 1972 made it impossible to keep the polar bears and sea lions in the Bear Mountain enclosure. This and its deteriorating condition lead to a $250,000 renovation of the exhibit starting in 1987. The exhibit reopened in 1989 with grizzly bears and Himalayan bears occupying the northern two exhibits and coatis in the southern tip.
In 1993 the zoo opened the $11.5 million Tropical Discovery exhibit. Designed by the Denver architectural firm Anderson Mason Dale, this indoor tropical garden topped by glass pyramids is the aquarium and herpetarium of the Denver Zoo, and its opening doubled both the number of species and the number of animals at the zoo. Along with the animals, 90% of which had never been on display at the zoo, there are over 250 species of plants represented in the exhibit.
On November 6, 1994, twin polar bear cubs Klondike and Snow were born to a first-time mother named Ulu, who rejected the cubs. They were successfully raised by zoo staff and became a popular attraction. The bears were transferred to SeaWorld Orlando, where Kondike still resides. In 2012 Snow was transferred from Sea World in Orlando, Florida to the Reid Park Zoo in Tucson, Arizona) where she died unexpectedly on Sept. 2, 2012.  Their story is commemorated at the Denver Zoo by a bronze sculpture located across from the main polar bear viewing area. 
On February 24, 2007, a jaguar mauled zookeeper Ashlee Pfaff inside the animal's enclosure. The jaguar was shot and killed by the zoo's emergency response team while rescuing Pfaff, who later died of her injuries at a local hospital. This event occurred despite zoo policy prohibiting direct contact between keepers and big cats. An investigation by the zoo concluded the attack was the result of human error by Pfaff.
In 2009, the Denver Zoo was the first zoo in the United States to achieve ISO 14001 certification. City park rebuilt its greenhouses in 2009, and as part of this project was able to provide the zoo with its own dedicated greenhouse.
In 2010 the zoo, in cooperation with the City and County of Denver, drained Duck lake in order to remove sediment buildup and improve its water quality. Duck lake is part of the 330-acre (130 ha) City Park but not part of the zoo, but it is a major nesting ground for black-crowned night herons and snowy egrets in the state. The nature walk along the lake shore was upgraded as part of the Asian Tropics project.
In 2012 the zoo opened the $50 million Toyota Elephant passage. The exhibit was originally announced in 2006 as Asian Tropics, and bids for a general contractor were sent out in June 2009. The exhibit was constructed by the Kiewit Building Group and groundbreaking was on December 2, 2009. It was opened to the general public on June 1, 2012.
The Denver Zoo houses species from all over the world, including hoofed mammals, carnivorous mammals, primates, pachyderms, birds, reptiles, and fish. The zoo is laid out in a large loop, with exhibits both inside and outside the loop. Current exhibits (in 2010) include the following:
Bear Mountain 
This historic exhibit, originally opened in 1918, is one of the first natural-style zoo exhibits in North America, and the first to use simulated concrete rocks. It underwent a $250,000 restoration between 1987 and 1989, and is now home to grizzly bears, Asiatic black bears, and coati.
Primate Panorama spreads over 7 acres (2.8 ha) and primarily houses apes and other larger primates. Tree-dwelling apes and monkeys live in open-air wire mesh tents that soar four stories high and cover more than an acre of ground. Inside these tents, the primates can play and climb on twisting vines. Gorillas roam freely, climbing ropes and taking afternoon hammock naps in one of the largest Gorilla habitats in the world. Orangutans have their own outdoor habitat where they can climb trees and swing in hammocks.
Jewels of the Emerald Forest pavilion features a meandering trail through diorama replicas showing four primate environments: Malagasy, South American forest floor and forest canopy, and primates of the night.
The nearby Shamba offers a view of a Central West African village and is home to red river hogs.
Monkey Island was built in 1937 with funds from the Works Progress Administration. It was rehabilitated in 1950. It is surrounded by a moat that also houses some aquatic birds (including Pelicans) in the summer. The moat is drained in the winter and the monkeys are housed in Monkey House.
Monkey house, facing Monkey Island, was the original primate exhibit in the zoo and currently still houses several species of monkeys, including those that are released on Monkey Island in the summer.
Predator Ridge is a large exhibit representing the African savanna. It has the ability to rotate different African predators (lions, hyenas, and African wild dogs), whose overlapping scents provide environmental enrichment for the animals.
Feline House was created in 1964 and comprises two buildings with three large outdoor exhibits and 6 smaller outdoor exhibits connected to the indoor rooms. Cats can retreat inside in inclement weather but be outside part of the time as well. The larger outdoor exhibits are currently inhabited by striped hyenas, maned wolves, and tigers. Other species on exhibit here include snow leopards (with three cubs born in 2008), dwarf mongoose, Amur leopards, servals, meerkats, and jaguars, and a fossa.
Cheetahs have their own large enclosure across from Pachyderm Habitat.
Pachyderm habitat 
Hoofed mammals 
Hoofed mammals are generally housed in the center of the zoo, though Sheep Mountain is in the North East corner. Hoofed mammals at the Denver zoo (counter-clockwise from the entrance) include Grevy's zebras, reticulated giraffes, Bactrian and dromedary camels, Mishmi takin, okapi, many species of antelope and deer, Dall sheep, bighorn sheep, and Cape buffalo.
Giraffe House was created in 1966 and, along with the outdoor Giraffe run, houses the zoo's giraffe herd.
Nearly 200 bird species, many rare and endangered, are exhibited in Denver Zoo's bird facilities, all of which are located next to or in Primate Panorama.
Bird World, opened in 1975, features open aviaries in which guests can mingle with exotic birds (and two-toed sloths). Each area features naturalistic habitats and replicated tropic and aquatic ecosystems, with three major exhibits built without barriers so the birds can fly freely among Zoo visitors. At the Bird World kitchen viewing window, visitors can see first hand what the birds eat. There are five outdoor exhibits directly attached to the exterior of Bird World which are home to African penguins, sea eagle, vulture, Egyptian vultures, Eurasian eagle owls, and a double-wattled cassowary.
Lorikeet Adventures, the Nurture Trail, and the Bird Propagation Center opened in 2006 between Bird World and the Primate Panorama. Lorikeet Adventure is a large open air "tent" where visitors can mingle with and feed lories and lorikeets. The Nurture Trail is a short trail between two large fenced areas: one for red-crowned cranes and one for secretarybirds. The trail then goes past two smaller outdoor enclosures attached to the Bird Propagation Center, which provides the Denver Zoo with facilities for breeding and raising all types of birds.
The Forest Aviary in Primate Panorama is a 7,500-square-foot (700 m2) area richly landscaped and enclosed in a nearly invisible wire mesh. Visitors can walk around inside with the birds, which include a black swan, black-necked swan, scarlet ibis (housed with the flamingos in the winter), Mandarin ducks, nene (or Hawaiian goose), and crested oropendola.
Along with these birds, peafowl roam the zoo, the parking lot, and the park outside.
Northern Shores 
Northern shores was opened in 1987 and features polar bears, North American river otters, California sea lions, and harbor seals. It was home to the famous polar bear cubs Klondike and Snow. Underwater viewing windows are provided in the Polar Bear and Sea Lion habitats.
Wolf Pack Woods 
Wolf Pack Woods is a large open "forest" that is home to a pack of Northern gray wolves.
Tropical Discovery 
Tropical Discovery was opened in 1993. This building contains numerous aquaria and various tropical mammals, amphibians, and reptiles, including chevrotain, vampire bats, cobras and vipers, poison dart frogs, arapaimas, capybaras, black howler monkeys, Siamese crocodiles, and Komodo dragons.
Toyota Elephant Passage 
Toyota Elephant Passage is a $50 million 10-acre (4.0 ha) exhibit. At its opening, it is the largest bull elephant habitat in the world, designed to house up to 12 elephants, 8 of them bulls. It houses Asian elephants and other animals such as the Indian rhinoceros, Malayan tapirs, and clouded leopards, which rotate among different habitats in the same style as Predator Ridge. The exhibit includes more than 2 miles (3.2 km) of trails for the animals, and pools in the exhibit contain a total of 1,100,000 US gallons (4,200,000 l). Gibbons swing directly over visitors, traveling between three islands. The exhibit includes an indoor facility for smaller species, and will provide breeding facilities for the Indian rhino and Asian elephant in North America. The exhibit opened with two female elephants (Mimi and Dolly) and two bull elephants (Bhodi and Groucho).
The exhibit is powered with a biomass gasification system, which will convert the zoo’s diverse waste stream of animal waste and human trash into a usable combustible gas. The gasifier will reduce the zoo's landfill contributions by more than 90 percent (1,500,000 pounds (680,000 kg)) and reduce energy use. The exhibit and its buildings have received LEED Platinum certification from the U.S. Green Building Council.
Other facilities 
The Endangered Species Carousel features hand-carved wooden replicas of some of Denver's most popular residents including a polar bear mom and cubs, giraffes, okapi and baby gorilla, along with many other endangered animals.
The Pioneer Train offers a quick trip around the zoo’s carousel meadow filled with beautiful lush foliage, under the shade of 100-year-old trees. Visitors can see American and Chilean flamingos and other waterfowl just outside the Primate Panorama exhibit. Denver Zoo’s Pioneer Train is the first natural gas-powered zoo train in the United States.
The animal hospital in Denver zoo was built in 1969.
The Gates Wildlife Conservation Education Center houses classrooms and meeting rooms for public and private (rental) use.
The Wild Encounters outdoor amphitheater is designed for wildlife presentations and is located just outside the Gates Center.
Education and conservation 
Throughout the day the Denver Zoo provides educational opportunities for visitors, including the sea lion demonstration, pachyderm demonstration, wildlife show, Wild Encounters, Predator Ridge demonstration, red river hog feeding, penguin feeding, Meet the Animal Stars, and others. Some of these are seasonal, and some (like the flamingo talk every day during the summer of 2009) showcase specific animals that have been raised at the zoo.
The Denver Zoo is part of the (American) Association of Zoos and Aquariums (AZA) Species Survival Plan for many species. As an active member of the World Association of Zoos and Aquariums (WAZA), Denver Zoo works with other zoos and aquariums around the world to respond to the global extinction crisis facing the world's frogs and other amphibians.
Denver Zoo's conservation efforts are coordinated by the Department of Conservation Biology. Through continued research and funding, the Department helps to conserve a variety of species worldwide. Although the zoo has been active in conservation and research since its founding in 1896, the establishment of the Department of Conservation Biology provides dedicated staff and funding to support hundreds of projects throughout the world.
Recent successes in captive breeding at the zoo include:
- Three maned wolf pups born in 2010, the first since 1985
- Twin emperor tamarins born in 2009
- Twin red pandas in 2008 and quadruplets in 2009
- 18 American flamingos hatched and raised in 2008 at the new Bird Propagation Center
Boo at the Zoo is held every Halloween and is great fun for Children.
Zoo Lights is open during December evenings. This is a spectacular stroll through a wonderland of lights, many of them animated and representing animals at the zoo.
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