Mystery as monkey gets pregnant despite being ALONE in cage for years – but baffled zoo keepers discover reason why

A MONKEY that fell pregnant despite being alone in a cage for years left zoo keepers mystified, and sparked a two-year investigation.

Momo the gibbon gave birth in 2021, which sent Japanese zoo investigators on a wild goose chase to find out who she had mated with.

But after a two year investigation, a piece of poo finally revealed who the father was.

The point of entry, however, still has zoo keepers baffled.

Momo was residing at Kujukushima Zoo and Botanical Garden, Nagasaki, at the time.

The white-handed gibbon was living in a cage with big bars cladded in chicken wire, separating it from the males next door.

Regardless, the 12-year-old gave birth to a black white-handed gibbon in 2021.

Through a DNA test, researchers analysed the poo of four prime candidates to workout who Momo's sexual pal was.

In the end, the father was a 34-year-old agile gibbon named Itoh.

Jun Yamano, zoo superintendent, told Vice News: "It took us two years to figure it out because we couldn’t get close enough to collect samples - she was very protective of her child."

Yamano said the point of contact was a hole in the wall with a nine millimetre diameter.

However, zoo keepers had no hard evidence of this.

Yamano said: "We think it’s very likely that on one of the days that Itoh was in the exhibition space, they copulated through a hole."

The zoo now hopes the intimate couple will be able to move in together.

Yamano said: "They have to get used to each other first.

"But hopefully they [will] live together as one family."