BOSTON -- Little Joe and Okie, two of Franklin Park Zoo’s western lowland gorillas, are avid finger painters and in an online world where almost anything can be found for sale, Okie's paintings are now up for bid on eBay.

Okie's finger painting is a part of the zoo’s enrichment program designed to keep the gorillas intellectually stimulated.

See The Gorillas' Paintings

Zookeeper Brandi Moores told The Boston Phoenix that she began encouraging the gorillas' art three years ago.

She sits on one side of the cage, the gorillas squat on the other.

Moores then squirts the paint onto the paper canvas and slides it under the gate. She choses the color. Okie smears the paint with his knuckles and sometimes adds his fingerprints to the art.

“I don’t know if Okie is painting thinking, ‘This is gorgeous,’ ” Moores told the paper. "Sometimes I just put the paint in the den with him and then I’ll leave him alone and he can do what he wants. I think it’s much more natural. He does just smear it around. He’ll smear it on the walls. He’s just kind of a messy gorilla.”

When he is done, Moores rewards the gorilla with slices of fruit.

Throughout the summer, Okie and Little Joe's work has been on display at the zoo, in the first public showing of their work in an exhibition entitled "Okie & Little Joe: A Retrospective."

Earlier this summer, one of Okie's paintings sold for $10,000 at a fundraising event at the zoo.

The bidding on eBay starts at $1,500 for each of the paintings. The auction ends late Saturday afternoon with proceeds benefiting the zoo.