A donkey savors warming temperatures after a long winter at the zoo in Warsaw, Poland, on Wednesday, April 8, 2015. (Photo by Czarek Sokolowski/AP Photo)
Talini (R), a 9-month old 160-pound polar bear cub, swims with her mother Barle at the Detroit Zoo's Artic Ring of Life exhibit August 25, 2005 in Royal Oak, Michigan. Talini's birth was the first polar bear birth at the Detroit Zoo in fifteen years. Her mother Barle was wild born and was rescued by the Detroit Zoo from a circus in Puerto Rico in 2002. (Photo by Bill Pugliano/Getty Images)
Mr. Ben, a pygmy slow loris, is administed anesthetic during one of Bristol Zoo's in-house veterinary clinic routine health check-up and teeth clean as part of the Zoo's standard animal husbandry and welfare procedure at Bristol Zoo on June 18, 2009 in Bristol, England. (Photo by Matt Cardy/Getty Images)
Two hippopotamus are fed with pumpkins at the Hanoi Zoo, in Hanoi, Vietnam, 25 October 2018. The zoo has been the home for more than 800 animals of over 90 different species, including three hippopotamus, since it was built in 1976. (Photo by Luong Thai Linh/EPA/EFE)