Central Park Zoo, New York, 1967. (Photo by Garry Winogrand)

A panda bear sits on a logs in a zoo on January 15, 2015 in Hangzhou, China. (Photo by Feature China/Barcroft Media)

A Chimpanzee opens its Christmas presents at ZSL Whipsnade Zoo on December 17, 2013 in Bedfordshire, England. (Photo by Tony Margiocchi/Barcroft Media)

A tiger yawns next to a piglet at the Sriracha Tiger Zoo, in Chonburi province, Thailand, June 7, 2016. (Photo by Chaiwat Subprasom/Reuters)

A keeper stands next to llamas during the Annual Stocktake at ZSL London Zoo in London, Britain February 7, 2018. (Photo by Tom Jacobs/Reuters)

A chevrotain or mouse deer feeds in its enclosure at Zurich Zoo, Zurich, Switzerland, October 17, 2012. (Photo by Patrick B. Kraemer/AP)

A chimpanzee bottle-feeds a lamb at Southam Zoo Farm in Warwickshire. The owners of the zoo, Mr and Mrs Clews, bring up many of the animals as their pets; the animals, are, as a result, of a friendly disposition. (Photo by Fox Photos/Getty Images). 23rd August 1968

Florence the baby zebra foal, runs in its enclosure at Edinburgh zoo September 4, 2008 in Edinburgh, Scotland. This arrival at the zoo is particularly important as the Grevy's zebra is listed as endangered, with only an estimated 1,500 to 2,000 remaining in the wild. (Photo by Jeff J Mitchell/Getty Images)