An employee’s negligence on the coldest night of the year in central Louisiana killed two tiny endangered tropical monkeys last month, a spokeswoman for the city of Alexandria said.

“As a result of this single person’s act of negligence we lost Kate, 12 years old, and her 2-year-old baby girl,” Jardon said. The 14-year-old male, Eddie, survived, Jardon said.

The employee had worked at the Alexandria zoological park since 2008 and admitted failing to properly check the cotton top tamarins on 7 January, Cynthia Jardon said.

The black-and-white monkeys, which have a fan of white hair on their heads, are among the smallest new-world monkeys, topping out at a little over a pound. They need temperatures of 76F to 85F. The overnight low early on 8 January was in the teens.

Eddie was the largest of the three monkeys and that bit of extra bulk may have saved his life, Jardon said. He has been at the zoo since May 2008, joining Kate, who arrived in November 2007. Their daughter was called “baby girl” but had not been named, she said.

“Zoos that specialize in endangered species rarely keep the offspring. They go to other zoos,” Jardon said in a telephone interview.

Jardon said the worker, whose name she did not know, resigned on 12 January after being asked to resign or be fired.

Cotton top tamarins are critically endangered, with about 1,800 in captivity and about 6,000 in a small area of northwest Colombia, according to the International Union for Conservation of Nature.

Primates have access to a heated building all day and are routinely locked into that building at night. But that night, Jardon said, the zookeeper skipped the tamarins.

“This has been a heartbreaking situation for all of us, including our zoo patrons, since these primates were loved by all who saw them and worked with them,” zoo director Lee Ann Whitt said in a statement emailed by Jardon.

The US agriculture department’s Animal and Plant Health Inspection Service checked the zoo on 21 January, according to a report forwarded by Jardon. The inspectors found that the zoo provided all required instructions and procedures for care of the monkeys, and did not find any fault with the tamarins’ exhibit or night house, Jardon said.

The report cited three problems at the zoo: the tamarins’ exposure to subfreezing temperatures; a cotton top tamarin and a red-handed tamarin each caged alone; and resting platforms in the tigers’ and cougar’s night quarters that needed repair.

“Clawed benches in cougar and tiger exhibits have been repaired,” and the solo monkeys get extra enrichment and extra time with a caretaker, Jardon wrote.

She said she did not know whether the zoo will get another mate for Eddie.