attack was the result of human error by Pfaff. For a short time in early 2007, the zoo's jaguar exhibit remained empty until the arrival of replacement jaguar Caipora. The zoo has not had jaguars since 2010. In 2009, 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. That same year, Denver Zoo celebrated the birth of an endangered aye-aye that was the first of the species to be conceived and born in a North American zoo. The zoo has continued to have a successful breeding program. 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 City Park but not part of the zoo. It is a major nesting area 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. In 2015, following conservation work around Lake Titicaca in Peru, Denver Zoo welcomed 20 Lake Titicaca frogs from the Huachipa Zoo and later became the first zoo outside South America to breed the rare amphibians. Some have moved to other institutions in hopes of building a healthy captive population that can be released back into the lake in the future. In nearby Colombia, the zoo released Andean condors in 2010 and 2012. Exhibits Denver Zoo houses species from all over the world, including hoofed mammals, carnivorous mammals, primates, pachyderms, birds, reptiles, and fish. The zoo's animal collection contains 3,500 specimens representing 550 unique species. The zoo is laid out in a large loop, with exhibits both inside and outside the loop. Current exhibits include the following: Primates Primate Panorama spreads over and primarily houses apes and other larger primates. Tree-dwelling apes and monkeys live in open-air wire mesh tents that soar