Zookeepers in Bristol have discovered a six-year-old Western lowland gorilla who was thought to be male is in fact female.

The surprising development became apparent when the primate, named Kukena, recently had her first reproductive cycle and her genitalia became more pronounced, Bristol Zoo said.

The discovery is hugely positive news for the species and the European Endangered Species Programme (EEP), as there are fewer female Western lowland gorillas than males in the world’s zoos.

John Partridge, senior curator of animals at Bristol Zoological Society, said: “We have a strict hands-off policy with our animals and as gorillas can be difficult to sex, Kukena had been thought to be a male.

“She is a healthy youngster and there have been no reasons to perform more invasive health checks on her during her lifetime in the zoo.

“This discovery will not change the way we manage our troop of seven gorillas at Bristol Zoo Gardens.”

Bristol Zoo’s animal team will discuss Kukena’s future with the gorilla EEP coordinator with the intention that she moves to another zoo within the next couple of years, to continue the breeding programme for this critically endangered species.