A baby bush-baby in a set of scales at London Zoo shortly after birth. (Photo by Fox Photos/Getty Images). 10th August 1938

A little girl takes a picture of a lion in the zoo in Frankfurt, Germany, Tuesday, September 13, 2016. (Photo by Michael Probst/AP Photo)

A zoo staff feeds crocodiles as visitors look on at the Malabon Zoo in Malabon City, north of Manila, Philippines 21 December 2017. Wearing Santa Claus hats for the upcoming Christmas season, owner Manny Tangco (R, holding megaphone) and some select animals gave visitors a tour of the 28-year-old zoo. (Photo by Rolex Dela Pena/EPA/EFE)

Khansa, an eight month old critically endangered Bornean orangutan shows off it's two front-teeth, at the Singapore Zoo on Thursday, January 11, 2018 in Singapore. The Singapore Zoo is active with its breeding programs as part of its wildlife preservation efforts. This is the Zoo's 46th successful orangutan birth. (Photo by Wong Maye-E/AP Photo)

An alligator named Muja is seen in its enclosure in Belgrade's Zoo, Serbia, August 14, 2018. Muja is officially the oldest American alligator in the world living in captivity. He was brought to Belgrade from Germany in 1937, a year after the opening of the Zoo. Muja survived three bombings of Belgrade, the Second World War and all hardships the Zoo went through. (Photo by Marko Djurica/Reuters)

A crocodile at a zoo in the southern Taiwan city of Kaohsiung holds the forearm of a zoo veterinarian in its teeth, April 2007. Surgeons in Taiwan have reattached a vet's arm, after it was bitten off by a crocodile as he tried to give it an anaesthetic injection. His attacker is one of a pair of Nile crocodiles kept at Shoushan zoo. Nile crocodiles are known to be man-eaters, but are also listed as an endangered species. (Photo by Frank Lin/Reuters)

An employee feeds a one-week-old coati cub with a bottle of milk at the Royev Ruchey zoo in the suburbs of Krasnoyarsk, Siberia, October 10, 2014. The mother of three cubs refused to nurse them, according to zoo employees. (Photo by Ilya Naymushin/Reuters)

A three month old white Bengal female tiger cub looks around her enclosure at the Buenos Aires Zoo, Argentina, Wednesday, April 16, 2014. Cleo, a captive Bengal white tiger at the zoo, gave birth to two females and one male white tiger cubs on January 16, 2014. (Photo by Natacha Pisarenko/AP Photo)