One chimp was seen wandering around the zoo paths, but most stayed on the wall surrounding their exhibit.
The chimps were returned to their inner enclosure.
The zoo staff are evaluating the trees in the primates' exhibit to see if they need to either be shortened or removed, the BBC reported.
This isn't the first time an animal at the zoo escaped its habitat. In January, a red panda was missing overnight but was discovered in a garden, The Guardian reported.