Zookeepers Finally Solve the Mystery of How an Isolated Gibbon Got Pregnant

Momo and her unnamed son, who was born in 2021. (Photo: Kujukushima Zoo & Botanical Garden)

When Momo the gibbon became pregnant two years ago, officials at the Japanese zoo where she resides were left scratching their heads. As the 12-year-old gibbon lives alone in her enclosure, they were unclear on how exactly she could have ended up pregnant. Now, thanks to DNA evidence, the mystery has been solved.

The female white-handed gibbon certainly has neighbors, but they are separated by two barriers. This made it difficult for zookeepers to understand what had happened. For several years they attempted to collect DNA samples from the male gibbon she gave birth to in 2021. But, Momo was understandably protective of her baby and wouldn't let them come close enough to collect the samples.

Finally, they were able to get samples not only from Momo's son, but Momo herself and four potential fathers that live in the vicinity. Now that the results are back, they can conclusively say that Itoh—a 34-year-old agile gibbon—is the father.

DNA solved one mystery, but staff at the Kujukushima Zoo & Botanical Garden still needed to figure out how the gibbons managed to mate. While there isn't any surveillance footage of what happened, zookeepers believe that the culprit is a small perforated board that separates Momo's enclosure from an exhibition area.

Itoh and Momo rotate out of the exhibition area in the morning and afternoon. The board is meant to prevent mating but does have nine millimeters holes. And, incredibly, staff believe that this is how they managed to procreate.

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

In order to attract Momo, Itoh would have had to go through some hoops. Gibbons are notoriously picky when it comes to choosing a mate, which is part of the reason that the staff is so shocked about what happened. These monogamous animals select their mates based on their appearance, social behavior, and elaborate vocalizations.

Now that the zoo has the full family picture, they're slowly working on having Itoh join Momo and her son.

“They have to get used to each other first. But hopefully, they live together as one family,” shared Yamano.

In the meantime, the zoo is not risking any more surprise pregnancies. The perforated board has now been replaced by a partition with no openings.

h/t: [Vice]

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