ST. LOUIS – Two swamp monkeys briefly escaped their enclosure at the Saint Louis Zoo on Saturday morning. It’s the third time that an animal has escaped its habitat in less than a month.

According to Billy Brennan, the zoo’s public relations director, the monkeys were out of their enclosure at the Primate House “for a short period of time.”

The monkeys’ habitat was left unlocked during routine cleaning, giving the animals a chance to sneak out, Brennan said. They found themselves in a keeper hallway that’s inaccessible to the public, and were soon returned to their enclosure.

The Primate House was temporarily closed to the public during the ordeal, Brennan said.

Allen’s swamp monkeys are native to west Central Africa and derive their name from the swampy forests where they live. Because they live near the water, the monkeys have developed webbed toes, which helps them paddle through the water. They live and congregate in groups of about 40 monkeys, and communicate through hand gestures and a series chirps, croaks, and grunts.

The zoo’s Animal Care team will review its safety and cleaning protocols in light of the incident.

Last month, an Andean bear named Ben twice escaped his enclosure at the Rivers Edge zone at the zoo.