Despite having been on birth control for years, a gibbon gave birth to a new baby on Nov. 12, at the San Diego Zoo, the zoo announced Friday.
It marks the seventh time Eloise the siamang, a species of gibbon, and her mate Unkie have become parents, the zoo said. Eloise had been placed on chemical contraception as a part of a coordinated effort to maintain genetic diversity in the zoo population of siamangs.
For years it worked – until Eloise gave birth earlier this month with little warning.
“It was amazing … she showed no outward signs of being pregnant,” a release quotes Jill Andrews, animal care manager at the San Diego Zoo.
Andrews likened the situation to when birth control fails for humans – it happens “from time to time.”
The zoo is celebrating the birth, the first siamang born at the zoo in more than 12 years, the release says. Siamangs are classified as endangered by the International Union for Conservation of Nature and Natural Resources.
The zoo says siamangs’ habitats are threatened by logging and agriculture; many adult siamangs are killed so that their young can be captured and sold as pets, according to the San Diego Zoo.
Siamangs are known for fiercely defending their young, the San Diego Union-Tribune reports.
Zoo officials say they don’t currently know the gender of the baby, as they have not yet separated the mother and child for a full exam. They expect that to happen in coming months.
The birth is surprising for another reason: Eloise is 37-years-old, far older than the 30 years siamangs are expected to survive in the wild, the Union-Tribune reports. In captivity, they have been known to live more than 40 years.
Contributing: The Associated Press
This article originally appeared on USA TODAY: Gibbon on birth control gives birth, much to the surprise of zoo keepers