Zoo Solves Mystery Of How A Gibbon Kept Alone In Her Cage Gave Birth

This isn't the beautiful tale you're picturing.

James Felton

James Felton

James Felton

James Felton

Senior Staff Writer

James is a published author with four pop-history and science books to his name. He specializes in history, strange science, and anything out of the ordinary.

Senior Staff Writer

A gibbon making some noise.

They had been gibbon all the clues. Image credit: Kurit afshen/

A Japanese zoo has solved the mystery of how a female gibbon in their care became pregnant while being kept alone in an enclosure. Before you get too carried away imagining a beautiful miracle, you should know that the answer was a glory hole.

In February 2021, Momo gave birth, surprising her keepers at the Saikai National Park Kujukushima Zoo & Botanical Garden, Japanese publication The Mainichi reports. In 2022, the zoo attempted to solve the mystery of who got Momo pregnant, collecting hair and excrement from Momo, her ape son, and four suspect males kept nearby, sending the samples for DNA testing at Kyoto University.


The test confirmed that one of the males, Itou, was the father. But how? The cages were separated by study bars and jagged chicken wire, according to Vice, making mating there pretty much impossible. However, during opening hours at the zoo, the gibbons are put on display in turns. Here, they are separated by a board partition. 

“We think it’s very likely that on one of the days that Itoh was in the exhibition space, they copulated through a hole,” zoo superintendent Jun Yamano told Vice.

Mating like this is almost more impressive than a miracle virgin birth. The perforated board separating the exhibition area and the backyard has holes of about 9 millimeters (0.35 inches) in diameter, according to The Mainichi. Following the glory hole use and subsequent birth, the zoo replaced the partition with a steel plate, with no holes.

A similar mystery that didn't end in "they had sex" took place in an Australian zoo in 2018, when an eagle ray gave birth despite not having been near a male in nine years. In this case, the ray reproduced via parthenogenesis.


  • tag
  • animals,

  • mating,

  • animal behavior,

  • gibbons,

  • Gibbon,

  • zoo,

  • mating behavior