Nov. 20 (UPI) -- The San Diego Zoo said the birth of a siamang ape came as a surprise to zookeepers -- especially since the mother was on birth control.
The zoo said Eloise, a 37-year-old siamang, a type of gibbon, had been on chemical contraception for several years after having six babies with her mate, Unkie.
The zoo said the surprise baby was the first siamang born at the zoo in more than 12 years. Officials said they had no idea Eloise was pregnant until she gave birth earlier this month.
"We're not certain why birth control didn't work in this case, but as with humans, it is not uncommon for contraceptive failure to happen from time to time," animal care manager Jill Andrews told the San Diego Union-Tribune. "Still, we are overjoyed -- because any birth of an endangered species is a reason to celebrate."
Officials said an examination will be performed in the next few months to determine the baby's sex.