Will and Grace were brought in from overseas for the breeding programme
Two endangered pied tamarin monkeys have been born at Colchester Zoo.
The twins, who have yet to be sexed or named, were born to parents Will and Grace who were paired last November as part of a rare breeding programme.
It is thought the population of the pied tamarin in the wild has fallen by half over the last 18 years.
"They're a very rare primate indeed, so we're absolutely thrilled to be successful with them so quickly," said zoological director Anthony Tropeano.
He added it would take a few months before they knew what sex the new arrivals were.
"The youngster's are fairly reliant on their parents for the first four or five months," he told BBC Essex.
"When they start to move off mum and dad and seem to be a little more independent, then we will look to see what sex they are."
The pied tamarin, which originates from the Manaus region of Brazil, is an endangered species on
International Union for Conservation of Nature Red List.
The parents of the babies, Will and Grace, had been deliberately paired together at
with Will coming from Canada and Grace transferred from France.
"There's a European endangered species programme for them, so the studbook keeper looks to match genetically compatible animals together," said Anthony.
"They use some software which matches animals that are as genetically diverse as is possible, so that you maintain as wide a gene pool in captivity as possible.
"The best match was these two animals, even they had to pair up from a fair distance apart."
Because of their nervous disposition, pied tamarin's are notoriously difficult to breed, according to Anthony.
"If they feel frightened, or threatened, or things aren't exactly right for them, then they will not breed and won't thrive," he said.
The baby monkeys will be reliant on their parents for several months
"So commercially, they're not the greatest exhibit in the world, but the primary consideration was that the habitat was absolutely right for them."
Anthony hoped the twins would, in time, be joined by some siblings.
"When they become a bit more independent of their parents, one would like to think their mum will come into season once again," he said.
"You'd then be looking at a period of about 170 days later that potentially we may have some brothers or sisters."