LULU GARCIA-NAVARRO, HOST:
Colombia has a hippo problem. Normally, these 4,000-pound beasts wallow in the lazy waters of sub-Saharan Africa, but in the 1980s, drug lord Pablo Escobar had money to burn.
EMMA CLIFFORD: Pablo Escobar had this idea that he could kind of create a Noah's Ark, if you like. And so he started collecting animals from all over the world and creating this personal zoo.
GARCIA-NAVARRO: That's Emma Clifford, founder and director of Animal Balance, an NGO focusing on controlling animal populations without culling them. She says among those walking two by two at Escobar's sprawling hideout were four hippos from Africa he smuggled into the country. After Escobar was killed in 1993, most of his exotic animals were moved to other zoos around the country but not the hippos.
CLIFFORD: The hippos were left because they're so large. They're rather difficult to move. And so the hippos continued to breed. And now there's estimated between 80 and 100 hippos living in the Magdalena River Basin area.
GARCIA-NAVARRO: Forty of them are still living at the Escobar estate east of Medellin, which has been turned into a kind of hippo amusement park attracting tourists. For the last year or so, Clifford's group has been working with local scientists to study these captive animals to try and figure out how to control the rest of the bunch, which are lumbering through the Colombian countryside, an invasive species for the ages. Despite the bad rap hippos have for being ornery, you know, never get between a hippo and its water, Clifford says locals have grown to love these interlopers and their contribution to the tourist economy.
CLIFFORD: And if the hippos come through the villages at nighttime, which is when it tends to happen, when they go for walkabout at nighttime, the people respect them and give them the space that they so deserve.
GARCIA-NAVARRO: And she says the hippos have scared away the illegal fishermen.
CLIFFORD: It used to be that they would use dynamite explosives for certain kinds of fishing. And now that's not happening. And so in some ways, the hippos are actually protecting the area of the river.
GARCIA-NAVARRO: But Colombia's lush lowlands are hippo heaven, and their numbers are exploding, according to Jonathan Shurin. He's a professor of ecology, behavior and evolution at the University of California, San Diego and is the leader of a team studying the hippos' impact on the rivers and lakes.
JONATHAN SHURIN: There was recently done a modeling exercise mapping their potential habitat, and that one estimated that they would top out in around one to two thousand or so animals once they've sort of filled all the available habitat around the Magdalena River.
GARCIA-NAVARRO: Fortunately, says Shurin, the hippos are hemmed in by the Andes, so they won't be showing up in the Amazon. But their growing numbers are a problem. Their feces trigger algae blooms and make the water toxic to fish. And with their massive appetites, hippos are competing for the same grasses and fruits eaten by native species. There were attempts in the past to cull the hippos, but locals were outraged after soldiers shot one. Now it's illegal to kill them. So scientists are working on a birth control plan for the pachyderms. It's no small task to sterilize these huge animals, but researchers hope that they will be able to lure them out of the lakes and rivers with some sweet carrots, dart them with a tranquilizer and inject them with a sterilizing chemical. If they are successful, says Shurkin, the days of the grandchildren of Pablo Escobar's hippos may be numbered.
SHURIN: Potentially, if you sterilize these ones and they stopped having new hippos, then these guys would live out their days. And then once these ones died, there would be no more.
(SOUNDBITE OF SONG, "HIPPOSONG")
AL STEWART: (Singing) I was surrounded by a large hippopotamus and nine other... Transcript provided by NPR, Copyright NPR.