The animal care team determined the baboons rolled a 55-gallon barrel upright near a wall of their open-air enclosure, then climbed it, which allowed them to escape.

The enclosure was built nearly 40 years ago, according to a news release from the facility.

Three baboons were recovered within 30 minutes. Officials initially thought a fourth remained on the loose but after completing a head count of all the animals determined it had returned to the enclosure almost immediately.

The barrel was put in the enclosure because the animal team deemed it an enrichment tool that helped baboons mimic foraging behavior, according to the release. After the escape, the staff removed the barrel and will determine if any modifications can be made.