Zoo staff members say the animals cannot burrow their way out because the former Kodiak bear environment is essentially a large concrete swimming bowl. The soil depth at Prairie Dog Town ranges from 6 feet to 8 feet.
"The dirt must be deeper than 36 inches in order for the prairie dogs to make their burrows under the frost line," Kranz said. "We took soil samples from the old exhibit so the soils could be matched exactly to what they were used to having."
After foiling the escape attempt, zoo workers adjusted wire fencing and installed more slippery plastic on the walls.
http://www.baltimoresun.com/news/maryland/baltimore-city/bal-md.ci.zoo12jun12,0,685569.story -via Boing Boing
(image credit: Kim Hairston/Baltimore Sun)