STOCKHOLM (AP) — People around the world were stunned when Copenhagen Zoo killed a healthy 2-year-old giraffe named Marius, butchered its carcass in front of a crowd that included children and then fed it to lions.

But Marius’ fate isn’t unique — thousands of animals are euthanized in European zoos each year for a variety of reasons by zoo managers who say their job is to preserve species, not individual animals. In the U.S., zoos try to avoid killing animals by using contraceptives to make sure they don’t have more offspring than they can house, but that method has also been criticized for disrupting animals’ natural behavior.