This concept image shows an aerial view of the proposed Zootopia in Denmark. The designer says the idea is to let the animals roam free, separated from visitors by hidden barriers. Bjarke Ingels Group hide caption

itoggle caption Bjarke Ingels Group

Arturo, the only polar bear in Argentina, lives in captivity at a zoo in Mendoza. The plight of the "sad bear" has spawned more than 400,000 signatures on a petition to get him moved to a "better life" in Canada. AFP/Getty Images hide caption

itoggle caption AFP/Getty Images

Arturo, the only polar bear in Argentina, lives in captivity at a zoo in Mendoza. The plight of the "sad bear" has spawned more than 400,000 signatures on a petition to get him moved to a "better life" in Canada. AFP/Getty Images hide caption

itoggle caption AFP/Getty Images

A curious cuttlefish stares back at the camera from inside The Smithsonian's National Zoo Invertebrate Exhibit. The exhibit, home to dozens of small aquatic and terrestrial species without backbones, closed on Sunday. Meghan Murphy/Smithsonian's National Zoo hide caption

itoggle caption Meghan Murphy/Smithsonian's National Zoo

After several news outlets reported that a man dressed as a gorilla was shot with a tranquilizer gun, a zoo in Tenerife, Spain, wants to be clear: There was no gorilla suit involved. Richard Thomas/iStockphoto hide caption

itoggle caption Richard Thomas/iStockphoto

The lions at the Copenhagen Zoo eat the remains of a healthy young giraffe named Marius in February. It's unclear whether the lion pictured was one of those euthanized. Kasper Palsnov/AFP/Getty Images hide caption

itoggle caption Kasper Palsnov/AFP/Getty Images

A security guard closes the gate at the Pittsburgh Zoo, where a 2-year-old boy was killed Sunday. John Heller/AP hide caption

itoggle caption John Heller/AP