Scientists Suspect Rain Is Killing Off Animals
By Hillary Rosner, The New York Times

Eduardo Carrillo was on a field trip to Corcovado National Park with a group of his biology students in November when he realized that something was wrong. In just over a mile, the group found five dead monkeys.

Three more were in agony, he said later -- emaciated, near death, sitting on the forest floor, unable to climb a tree.

"I had never seen something like this," said Carrillo, a wildlife ecologist at the University of Costa Rica. At first, he suspected yellow fever, which swept through monkey populations in the 1950s. So he hurried back to San Jose, the capital, and convened a team of scientists, which included wildlife biologists, a microbiologist, a geneticist, and a veterinarian.

Tourists in the park, a relatively remote 212-square-mile tropical rain forest preserve that stretches along the Pacific coast and inland, reported sightings of other dead animals, including deer, toucans, macaws and sloths.

Carrillo and his colleagues, as well as government officials, worried they might have a mini-epidemic on their hands. But tissue samples from Corcovado spider monkeys -- Costa Rica's most endangered species of monkey -- showed no evidence of a virus or other pathogen.

The story of what really happened in Corcovado, or at least the prevailing theory, is less worrisome in the short term than a disease outbreak, but it has the potential to be deadly serious.

Costa Rican researchers think the affected animals starved to death because of a lack of available food sources and an inability to forage for food during several months of extreme rain and cold.

September, October and November brought excessive rainfall, almost twice the monthly averages, and unusually low temperatures to many parts of Costa Rica, especially the Osa Peninsula, which juts into the Pacific in the south.

Corcovado averages about 24 inches of rain in September, 31 inches in October, and 20 inches in November. In 2005, more than 39 inches fell in the park in September, 59 inches in October, and 41 inches in November.

While it is impossible to know if the weather in late 2005 is related to climate change, the Costa Rican team studying Corcovado worries that if the climate changes and produces more extreme weather events like this, animal populations may not bounce back easily, said Gustavo Gutierrez-Espeleta, a wildlife population geneticist at the University of Costa Rica.

The weather caused several problems for the monkeys. Some fruit trees did not bear fruit during the rainy months. Others produced fruit, but it fell to the ground early, leaving nothing on the trees for long periods of time.

Compounding the problem, researchers say, was that monkeys were unable to look for food because of the incessant rain.

"If you have a long period of days where it's raining, raining, raining, they just stay in the tree waiting, and they don't eat," said Grace Wong, a wildlife conservation researcher at National University in San Jose.

"The monkeys need sun to dry off," said Ronald Sanchez Porras, an ecologist at the University of Costa Rica. "You can see in the tree when the monkey moves his body to try to shake the water off. But when it rains like this, it's impossible."

Four species of monkeys live in Costa Rica, and all four are found in Corcovado.

The squirrel and capuchin monkeys rely on a diet of fruit, insects, leaves and stems; howler monkeys mainly eat leaves. The spider monkeys consume a diet almost exclusively of fruit, leaving them the most vulnerable.

In addition to being hungry, the monkeys that died were severely dehydrated, apparently having been unable to venture down from the trees for water.

This may have stressed their immune systems to the brink, causing parasites and infections that occur normally to become deadly.

Animals living near the edges of the park or outside the park in nearby privately owned rain forests seemed to fare better than those living deep in the park, probably because they had access to fruit trees and other crops planted by people.

"I never saw toucans here before, but they were fighting outside my office because we have banana trees," said Marleny Jimenez, who owns the Drake Bay Wilderness Resort, a tranquil getaway at the headwaters of the Rio Agujas, about five miles up the coast from Corcovado.

While some estimates hold that as many as half the spider monkeys in Corcovado died in the last few months of 2005, the scientists cannot be certain, in large part because it is not known exactly how many animals live in the park.

The Wildlife Conservation Society and Conservation International provided money for research into the animal deaths and will pay for follow-up visits to the park every other month.

Researchers then will tag monkeys to keep tabs on troop populations and mark trees to monitor fruit production.

"The lesson is that we should document as much as possible from now on with this kind of event and try to establish a link to the climate change process," said Carlos Manuel Rodriguez, Costa Rica's minister of the environment and energy.

For several decades, Costa Rica has had a strong record of natural resource protection, with strict rules on what sort of resource extraction is allowed on private lands.

"Costa Rica is committed to reversing the process of climate change," Rodriguez said, citing the country's rain forest preservation efforts, ban on oil drilling and interest in renewable energy.

"We don't see the rest of the world doing a good job," he added.

Corcovado's starving monkeys, the Costa Rican scientists worry, may be early messengers of future problems associated with a changing climate.