The six cotton-top tamarins found dead at the Oregon Zoo last month probably died of stress-related shock after traveling for at least 50 hours in a van from the East Coast, zoo records say.

Zoo officials then put the endangered monkeys in plastic picnic coolers with air holes cut in them at the zoo's veterinary facility—a practice questioned by primate keepers after six of the nine monkeys died May 24, two days after arriving in Portland.

Zoo documents show veterinarians and keepers blaming each other in the wake of the monkeys' deaths, the latest stumbles at the zoo. The records also offer an unusually close look at the hazardous practice of shipping rare animals cross-country.

The records, including pathology reports and communications between zoo staff, were released by regional government Metro in response to an information request made by WW last month under Oregon records law.

The records are heavily redacted, because the organization that donated the monkeys to the Oregon Zoo—widely reported to be Harvard University—refused to waive a non-disclosure agreement. 

(UPDATE, 6 pm: Harvard Medical School has released a statement defending the van shipment of the monkeys—along with a letter from a Oregon Zoo keeper speculating the tamarins may have died from "off-gassing" in the plastic coolers.)

The deaths of the monkeys are among a series of upheavals that have rocked the Oregon Zoo in recent months. In May, Metro fired its zoo director and chief veterinarian, saying they didn't disclose facts related to the death of a Sumatran orangutan.

Cotton-top tamarins are are a critically endangered species, and one of the rarest primates in the world. Only about 6,000 remain in their natural South American habitat.

The nine tamarins—six females and two males, along with a baby of undetermined gender—arrived at the zoo on May 22. Medical records show they had traveled by van for 50 hours, though minutes from a later staff debriefing say the travel time was 58 hours.

Keeper reports say the monkeys appeared healthy, although "very excited and skittish." They were placed in quarantine for observation, a standard practice.

But on 3 pm May 24, veterinary technician Margot Monti found six tamarins—five females and one male—dead inside the plastic coolers the zoo had provided as nesting boxes.

"I could see one of the animals' heads sticking out of the entrance," Monti writes, "but it was not moving so I gently shook the box. When there was still no reaction, I touched the top of the animal's head with gloved hand and found it to be stiff and cold."

In pathology reports on the dead animals, veterinarian Michael Garner says the monkeys' condition was "consistent with acute systemic shock" and suggested travel stress as a likely but not proven cause. (Garner wrote the reports since the zoo's chief veterinarian, Mitch Finnegan, was fired early last month after the death of Sumatrian orangutan Kutai.)

But Garner also kept open the possibility that the tamarins died from heat stroke or breathing in toxins.

Veterinary staff, who have been defending themselves against Metro's charges of "sloppy" procedures in the final surgeries on Kutai, cast aspersions on the primate keepers—especially Jennifer Davis, the zoo's curator of primates and Africa exhibits.

Monti, the veterinary technician, added to her report on May 27 that Davis had done nothing to help the surviving three tamarins, and that Davis declined to call the donor of the animals because "I'm afraid I might cry."

Meetings in the days after the tamarins' deaths focused on whether zoo curators should have allowed the shipment of the monkeys by van.

Minutes from a May 28 meeting show deputy zoo director Chris Pfefferkorn questioned that method of transport.

Davis explained that the monkeys' donor "insisted the tamarins be driven as they had done this successfully four times before. They had successfully transported tamarins to the Oakland Zoo previously by driving the animals from Massachusetts."

She said she asked the tamarins be flown west, but the donor refused and said it still owned the monkeys.

Pfefferkorn replied that "he did not care who they belonged to, his expectation was that the Oregon Zoo Curator take responsibility for making sure transports are done in the best possible fashion for the animals."

(This is not the first animal death involving a highway shipment to the Oregon Zoo. In 2008, a zoo employee drove a female black rhinoceros cross-country, and it died in the back of a truck outside Phoenix. The zoo said it would reconsider how it shipped animals, to keep the trips as short as possible.)

Meanwhile, Davis wrote a memo May 29 saying the organization that donated the monkeys—likely Harvard—wanted to warn other zoos not to use plastic coolers for nest boxes.

"As you know those coolers are meant to be air tight for food and drinks, without proper venting that allows circulation (not just a single hole cut)," Davis wrote. "I personally believe they could be dangerous, especially depending on the size and number of animals."

The tamarin family that arrived at the zoo May 22 was described in a transfer form as being healthy and active.

"The whole family group is very social, curious and love to play," the donor form to the Association of Zoos and Aquariums says. "They come right up to anyone that approaches….When the offspring were younger there was some issue with chewing on tails however, this has resolved itself and there are no aggression issues."

The three surviving monkeys, including an infant, remain in the care of the Oregon Zoo.