More than half of the monkeys bred for medical research that escaped a compound in South Carolina last week have been recaptured.
Twenty-four monkeys were captured on Sunday, a day after another of the 43 escaped monkeys was recovered.
The first monkey to be found was a female in a trap on the Alpha Genesis facility's campus and was unharmed.
In a statement, CEO Greg Westergaard said: "She is safe and sound and has since had a peanut butter and jelly sandwich."
Twenty-four more were then recaptured unharmed on Sunday US time.
Veterinarians have been examining the animals and initial reports indicate they are all in good health, police said.
The company has vowed to capture the remaining rhesus macaques unharmed.
So what is Alpha Genesis and how did this happen?
How did they escape?
In a statement posted on its Facebook page, the Yemassee Police Department said the rhesus macaques escaped from their enclosure after a caretaker failed to secure the doors.
The animals escaped from a research centre called Alpha Genesis, who conduct "bio-research services".
Greg Westergaard, CEO of Alpha Genesis, told NBC News: "The incident yesterday involved a new enclosure, and occurred because the caretaker who was doing routine cleaning and feeding failed to secure two separate doors. It was purely human error."
Alpha Genesis confirmed with police that the monkeys were all young females, had never been used for testing, and were too young to carry disease.
What are the plans to capture the monkeys?
A "sizeable group" remains active along the compound's fence line and bedded down in the trees for the night, police in Yemassee, about 80 kilometres north-east of Savannah, Georgia.
Alpha Genesis CEO Greg Westergaard said that efforts to retrieve the remaining monkeys will continue "for as long as it takes."
The company hopes that one-way traps containing apples will entice the remaining animals.
Born Free USA, an animal welfare and conservation organisation, released a statement last week inviting Alpha Genesis to work with them to rehome the monkeys to a sanctuary.
"We are deeply concerned for the welfare of the 43 monkeys who have reportedly escaped from the Alpha Genesis facility in South Carolina," CEO Angela Grimes said.
"The monkeys are vulnerable, with no experience of living outside of their captive environment.
"As wild animals, they also pose a risk to humans, with a particular threat of zoonotic disease spread. We are reaching out to Alpha Genesis today to invite them to work with us to rehome the monkeys to sanctuary, where they can live out their days in safety."
At the moment, those living in surrounding areas are being asked not to interact or feed the monkeys and call local authorities if they spot one.
What are the monkeys being used for?
Alpha Genesis is a facility that breeds the rhesus macaques to sell to medical and other researchers.
The facility, in Yemassee, a small town in South Carolina, has more than 100 acres of quarantine, holding and research space.
On the company's website it says it "provides the highest quality non-human primate products and bio-research services world-wide."
It also provides numerous "non-human biological products" including serum, plasma, whole blood, peripheral blood mononuclear cells and tissue samples.
Alpha Genesis says it has clients across North America, Europe and Asia.
Why are rhesus macaques used for research?
Rhesus macaques are among the most studied animals on earth.
For over 100 years they have been researched due to their similarities to humans through their clever behaviour, organ systems and genetic code.
Animal rights groups point out that the species has been subjected to studies on vaccines, organ transplants and the impact of separating infants from mothers.
At the same time, many in the scientific community will tell you just how vital their research is to fighting AIDS, polio and COVID-19.
In 2003, a nationwide shortage of rhesus macaques threatened to slow down studies and scientists were paying up to $10,000 per animal to continue their work.
“Every large research university in the United States probably has some rhesus macaques hidden somewhere in the basement of its medical school,” according to the 2007 book, “Macachiavellian Intelligence: How Rhesus Macaques and Humans Have Conquered the World."
“The US Army and NASA have rhesus macaques too,” wrote the book's author, Dario Maestripieri, a behavioural scientist at the University of Chicago.
"And for years they trained them to play computer video games to see whether the monkeys could learn to pilot planes and launch missiles.”
For those who have studied the behaviour of rhesus macaques, the research is just as interesting.
"They share some striking similarities to ourselves in terms of their social intelligence," said Dr Maestripieri, the University of Chicago professor who wrote a book on the species.
For example, the animals are very family oriented, siding with relatives when fights break out, he told The Associated Press on Friday. But they also recruit allies when they're attacked.
"They're very political," Dr Maestripieri said.
Has this happened before?
This is not the first time primates have escaped from the facility.
In 2018, federal officials fined Alpha Genesis $US12,600 ($19,137) after dozens of primates escaped as well as for an incident that left a few others without water and other problems with how the monkeys were housed.
Officials said 26 primates escaped from the Yemassee facility in 2014 and an additional 19 got out in 2016.
