Denver Zoo is an nonprofit zoological garden located in City Park of Denver, Colorado, United States. Founded in 1896, it is operated by the Denver Zoological Foundation and funded in part by the Scientific and Cultural Facilities District (SCFD) in addition to ticket sales and private donations. It is the most visited paid attraction in Colorado. 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, featuring huge mesh tents and open areas for apes and monkeys, and with 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. Denver Zoo is accredited by the (American) Association of Zoos and Aquariums (AZA) and American Humane and is also a member of the World Association of Zoos and Aquariums (WAZA). The zoo achieved ISO 14001 certification in 2009, was given the first AZA Green Award in 2011, and was named the "Greenest Zoo in the Country" at the World Renewable Energy Forum in 2012. In 2015, it was re-certified for ISO 14001 and achieved OHSAS 18001 certification, becoming only the fourth zoo in the world to get both certifications. History Early years 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, antelope which roamed the park, and a flock of Chinese pheasants, which later populated the eastern plains of the state. As this collection grew, the newly-formed park board continued to focus almost exclusively on acquiring native animals (with a notable pheasant collection and rhesus macaques as the exceptions) and some of the most popular animals at the park were large herds of bison and elk. In 1905, a population of red squirrels was added to the