Kansas City Zoo visitors were locked up indoors for an hour Thursday while seven chimpanzees ran free outdoors in an area accessible only to zoo personnel.
Zoo Director Randy Wisthoff told TV-9 the chimps using a tree branch for a ladder was an example of primate intelligence and strength.
"Chimps are so much stronger than humans that they can go up in a tree and pull on something long enough and pull a piece of log off, that's apparently what happened," he said.
Wisthoff said zoo visitors were never in danger, but precautions were taken in case the chimps displayed further engineering skills.
With dinner time approaching, the seven wayward apes were lured back into their enclosure with fruits, veggies and for one last simian holdout, malted milk balls.