Ants carry a leaf with a slogan reading “Merkel, Help!”, a reference of German Chancellor Angela Merkel, at the zoo in Cologne, Germany August 18, 2015. Some of the zoo's 500,000 leaf-cutting ants carry laser-cut leaves with slogans during a campaign to protect the Amazon rain forest, organised by the German branch of World Wild Fund for Nature (WWF) and Cologne Zoo. Picture taken through the glass of the display case. (Photo by Ina Fassbender/Reuters)

A Bengal tiger licks a glass enclosure during a presentation of Bengial tiger cubs at the Malabon Zoo in Malabon City, north of Manila, Philippines, 14 July 2016. The Bengal tiger cubs, which were born at the zoo, are two months old and named “Tiger Duterte” and “Tiger Leni”. The Malabon Zoo has one of the largest private collections of exotic and endemic animals in the Philippines. (Photo by Mark R. Cristino/EPA)

Western lowland gorilla Kijivu holds her newborn baby at the Prague Zoo in the Czech Republic. (Photo by Isifa/Getty Images)

A shoebill is displayed at Ueno Zoo in Tokyo August 28, 2012. (Photo by Itsuo Inouye/Associated Press)

Two chimpanzees share a piece of watermelon at Taronga Zoo on December 23, 2010 in Sydney, Australia. (Photo by Rick Stevens/Taronga Zoo via Getty Images)

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)

Two three-month-old female white Bengal tiger cubs play with a zoo keeper in their enclosure at the Buenos Aires' Zoo, in Argentina, on April 17, 2014. Captive white Bengal tiger Cloe, gave birth to three cubs – two females and one male – on January 14, 2014. (Photo by Juan Mabromata/AFP Photo)