save wild populations of the endangered Lake Titicaca frog and Lake Junin giant frog. Amphibian experts with the zoo have had rare success breeding boreal toads, listed as endangered in several western states, and have released over 600 young toads in southwestern Utah. In 2021, the zoo and Colorado Parks and Wildlife partnered to launch a program aimed at increasing the boreal toad population of the state. Denver Zoo also has a storied history with the American bison as it was one of the first zoos to assist in nationwide efforts to save the species from extinction. A breeding herd of five bison arrived at the zoo in 1899. The zoo no longer houses the species but manages a herd on the Rio Mora National Wildlife Refuge in New Mexico and also contributed animals to both the Genesee herd near Denver and the Heartland Ranch herd near Lamar. The latter herd, behaving naturally on thousands of acres and with the help of the Southern Plains Land Trust, almost entirely returned the ecosystem to its natural state as of 2019. 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. Events 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. Notes References External links Denver Zoo Audio Tour Tourist attractions in Denver Zoos in Colorado 1896 establishments in Colorado Works Progress Administration in Colorado Parks in Denver Buildings and structures in Denver Zoos established in 1896