SASEBO, Nagasaki -- The unexpected birth of a baby gibbon has left zookeepers scratching their heads and asking: who's the father?
In February, Momo, a 10-year-old gibbon -- about 20 in human years -- gave birth at the Kujukushima Zoo & Botanical Garden Mori Kirara in Sasebo, to the surprise of her caretakers, who did not realize she was pregnant. Kept in her own pen, out of contact with male counterparts, the birth at first seemed like a case of immaculate conception. As visitors celebrate the cute new arrival, the zoo says it plans to conduct a paternity test to get to the bottom of the monkey business once and for all.
On the morning of Feb.10, a zookeeper entered the gibbon pen and saw a newborn baby clinging to Momo's belly.
"I couldn't help but exclaim in shock. I was so startled, I thought I was dreaming," the zookeeper said.
Momo belongs to a species of endangered lar gibbon, also known as the white-handed gibbon, which are listed as threatened with extinction on the International Union for Conservation of Nature's Red List.
As the species does not usually show obvious weight gain or other external signs of pregnancy, the staff did not notice anything was amiss.
The zoo's nine adult gibbons are kept in a three-room animal house. However, to avoid inbreeding and crossbreeding, each room was partitioned off by boards and wire mesh, making it impossible for the creatures to travel back and forth.
One end of the enclosure was occupied by Yotaro, Momo's father, who resides with two females as the only other male white-handed gibbon at the zoo.
The other end held a room of siamangs, another species of gibbon, where the three males – Curly, Kakeru and Noboru – cohabited with a female of their own.
Momo was kept in the middle enclosure, with the plan to have her mate with males from other zoos in the future.
Although Momo shared her room with Itou, a male agile gibbon, the two were kept physically separated, and were never supposed to be able to interact. Whenever one was in the display room, the other would have been in a walled-off sleeping room.
Over the course of several meetings to identify how Momo could have become pregnant, the zoo narrowed down the possibilities to some small gaps in the dividers between rooms.
Each of the three rooms were divided by wire mesh with openings measuring about one centimeter across, and the partitions specifically separating the sleeping room from the rest of Momo's space also had several holes with a diameter of nine millimeters.
"Mating through the gaps is unlikely, but we can't think of any other possibilities," said zoo director Chikako Iwaoka.
"The reproductive organs of male gibbons are about the size of a human pinkie finger, and mating takes only a few seconds in some cases," said Koshiro Watanuki, a curator at the Japan Monkey Centre in Aichi Prefecture, who is familiar with the biology of gibbons. "This would be a very rare case, but it's possible."
But which gibbon is the baby's father?
According to Watanuki, the siamangs are unlikely to be the father, as it is genetically difficult for white-handed gibbons and siamangs to successfully procreate.
Yotaro would also be unlikely to be interested in Momo next door when he already lives with two females in the same space, Watanuki added.
By process of elimination, the circumstantial evidence would seem to point to Itou.
The zoo plans to conduct a DNA test in a year or so, once the baby has been weaned.
"We need to reflect on how this pregnancy was allowed to happen, as it was not part of the breeding plan," Kumiko Fukuda, an official at Sasebo Pearl Sea Co., which operates the zoo.
"However, the baby is doing well. Alongside zoo visitors, we hope to watch over Momo's parenting and the baby's growth."
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