Pablo Escobar had a private zoo at his estate in Colombia, with zebras, giraffes, flamingoes - and four hippopotamuses. After Escobar was killed in 1993, most of the animals were relocated except for the so-called "cocaine hippos." Authorities thought they would did but they did not and now, about a hundred roam near the estate. Conservationists are trying to control their population because they worry about the people and the environment. But some locals like the hippos and a few researchers say the animals should be left alone and are filling an ecological void. The controversy reflects growing debate in ecology about what an invasive species actually is. Contact Short Wave with your animal stories at shortwave@npr.org.