More bad news for the Oregon Zoo, which recently fired its director and chief veterinarian after "sloppy" medical treatment led to the death of Kutai, a 230-pound orangutan. 

newly-acquired monkeys were found dead in quarantine at the zoo's $8.8 million veterinary medical facility on May 25, three days after arriving at the zoo on loan from Harvard University.

Jim Middaugh, a spokesman for Metro, the regional government that operates the publicly-owned zoo, has confirmed the death of the six cotton-top tamirins to WW.

The deaths add to the unwelcome spotlight on the zoo's stumbles, examined by WW in this week's cover story.

Since the beginning of 2013, 27 of the zoo's 329 mammals have died—including two gibbons, two gazelles, a sea lion and a tiger. (That doesn't count the six monkeys.)

It's difficult to say if the Oregon Zoo has a better or worse track record than other zoos on animal mortality. Since 1994, zoos and aquariums haven't been required to inform the U.S. Department of Agriculture when their animals die.

Six cotton-top tamarins - a species of small New World monkey - died of unknown causes this weekend while in quarantine at the Oregon Zoo's veterinary medical center. The six deceased belonged to a group of nine tamarins that arrived at the zoo May 22. The remaining three, including a 5-week-old baby, appear to be in good health and are being closely monitored. The deaths were discovered by vet staff early Sunday morning. Initial necropsy results were inconclusive, and tissue samples have been submitted to a pathologist for analysis. Zoo officials hope to receive the results within a few weeks.