A zookeeper feeds a hippopotamus with a watermelon in its enclosure in Belgrade's zoo, Serbia, July 20, 2015. Temperatures in Serbia have risen up to 40 degrees Celsius (104 degrees Fahrenheit), according to official meteorological data. (Photo by Marko Djurica/Reuters)

Newborn sea lion “Kaya” crawls at the enclosure at the zoo in Wuppertal, Germany July 23, 2015. Kaya was born on July 4, 2015 in the zoo, officials said. (Photo by Ina Fassbender/Reuters)

A spider monkey eats a mango at the Paraguana zoo in Punto Fijo, Venezuela July 22, 2016. Some 50 animals have starved to death in the last six months at one of Venezuela's main zoos due to chronic food shortages that have plagued the crisis-stricken South American nation. (Photo by Carlos Jasso/Reuters)

Baby clouded leopards, born early in March 2015, are presented by zoo keepers at the Olmense Zoo in Olmen, Belgium, April 16, 2015. The clouded leopard is an endangered species with only some 10,000 specimen remaining on earth, said Robby Van der Velden, a biologist at the Olmense Zoo. (Photo by Yves Herman/Reuters)

A German contestant adjusts his helmet during the “Battle of Nations” in Aigues-Mortes, southern France, Friday, May 10, 2013 where Middle Ages fans attend the historical medieval battle competition. The championship will be attended by 22 national teams, which is twice the number it was last year. The battle lasts until May 12. (Photo by Philippe Farjon/AP Photo)

Papier-mache pandas, created by French artist Paulo Grangeon, are covered with conical hats as they are displayed under the rain at the financial Central district in Hong Kong June 21, 2014. The installation arrived in the city on Monday, launching the month-long “1600 Pandas World Tour in Hong Kong: Creativity meets Conservation” organized by a local art organiser, according to the official press release. (Photo by Tyrone Siu/Reuters)

The first jaguar litter since 1975 was born at the Milwaukee County Zoo to Stella and Pat on November 13, 2013. The litter was on public display for the first time on March 13 when the jaguar baby's names were released. Belize schoolchildren named one Zean, which is the end of Belizean, and a public contest named the other B'alam, which means "great and powerful king" in Mayan. Photo: Stella the mother and her cub Zean rest together at The Milwaukee County Zoo. (Photo by Rick Wood)

A West African Slender-snouted Crocodile is pictured in its enclosure at the zoo of Abidjan, Ivory Coast September 9, 2016. (Photo by Luc Gnago/Reuters)