May 28, 2013 -- In the bustling streets of a Colombian village, colorful exotic birds, monkeys and sloths, all animals that were once wild, are being sold as pets, and business is booming.
The wildlife trade is now the third-most-lucrative criminal enterprise in Colombia after drugs and weapons. An estimated 60,000 animals were trafficked last year alone, including a growing number of sloths.
What's more, traffickers are fueling a growing economy that is thriving outside of Colombia. The global market for wild animals, and that includes the United States, is estimated to bring in $20 billion per year.
In what is now considered the biggest exotic pet seizure in American history, 27,000 animals, including several sloths, were rescued from a pet distributor in Arlington, Texas, in 2009. Undercover video shot by PETA members showed that the sloths were kept in filthy cages that lacked the necessary equipment for the animals to survive in captivity, including heat lamps and humidifiers. The bodies of several sloths were later found in the facility's freezer.
It was a sad reminder, zoologist Lucy Cooke said, of the most common misconception about sloths.
"They did not evolve to be somebody's house pet," Cooke said. "Sloths make lousy pets. That's the truth of it."
She described it as the curse of being cute. Behind their easygoing nature, an apparent fondness for hugs and that perpetual smile, is a highly specialized biology that leaves sloths largely unable to survive outside the rainforest, especially because they survive on a complicated diet of about 40 different plant species.
"They're highly specialized animals," Cooke said. "That's why you don't find them in zoos. You don't find three-fingered sloths in zoos in the States because they're so difficult to keep. So the idea that any old Joe could just keep one as a pet is a bit of a fantasy, really."
"Nightline," along with Cooke, went an undercover investigation to Cordoba, a region of Colombia notorious for its illegal wildlife trade, where sloths are one of the hottest items for sale, to see how rampant the wild animal trafficking had become.
Samuel, our local guide, said traffickers operate there with impunity because paramilitary groups still control much of the area and police rarely get involved.
A few miles past an empty police station and a giant "No Trafficking" sign were men suspected of selling wild animals. One man was pushing exotic wild parrots, who were tied down and had their wings clipped to prevent them from flying away. Another was offering to sell a howler monkey.
Another was selling sloths for about $30 each, and pulled one out of his bag to show it off.
When a car suddenly pulled up next to us, the traffickers scattered, but it turned out to be a false alarm. Supposedly, it was the mayor of a nearby town who wanted to take a photo with the sloth.
Then, we got word of another suspected trafficker who had sloths for sale outside of a house. When we arrived, a family of pale-throated sloths, a mother with two babies, was being sold together, all three kept in one crate.
It was a bittersweet moment for Cooke.
"I've never actually seen a pale-throated sloth before," she said. "It's taken all my life to see one. I've never really expected that this would be the scenario that I'd see one for the first time."
"I'm going hold it together, but I feel very sad," Cooke added.
We were faced with a decision, and it was a dicey situation. The traffickers surrounded us and they were expecting a sale, but could we just walk away or should we try to rescue the sloth family?
What will Lucy Cooke and the "Nightline" team decide to do? Click HERE to watch what happened.