A monkey escaped from its enclosure in Belfast Zoo on Sunday night.
Colobus monkeys come from Mount Kilimanjaro
A man phoned the police when he spotted the Colobus monkey climbing in his back garden.
The two foot tall, black and white animal is described as a shy, nervous species, but should not be approached.
The man, Johnny Owens, also telephoned his nieces who came over and fed the ape. "I couldn't believe my eyes," he said.
The zoo began its search the following morning as the monkey had already settled for the night.
Mark Challis is the acting manager at Belfast Zoo, and he hopes that the young male monkey will be returned safely.
"He's out of his normal environment, he's likely to want to hide," he said.
He urges anyone who spots the animal to keep their distance, but to keep an eye on him.