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The Agouti's Nutty Friend

A small rodent and the towering Brazil nut tree have one of the most important relationships in the Amazonian forest

  • David Taylor
  • Mar 01, 2000
WALKING UP a narrow trail through the tangled undergrowth of the Peruvian rain forest, we came across a small piece of puma scat on our path. It was early and the forest was quiet, and I was looking for an agouti, a cat-sized rodent and subject of Enrique Ortiz´s recent research. But when the puma scat prompted Ortiz to tick off a list of predators in the area­­jaguars, pumas, harpy eagles, anacondas­­I wondered, "Why are we concerned with agoutis?"

"Because none of the others can break open a Brazil nut pod," said Ortiz, a biologist now working at the Smithsonian Institution´s National Museum of Natural History in Washington, D.C. Ortiz was exploring one of the strangest and most influential relationships in the Amazonian forest, and I was tagging along. The towering Brazil nut tree (as tall as 150 feet) and the diminutive agouti (about 1 foot tall) make perhaps the world´s most extreme Mutt-and-Jeff team, each dependent on the other for its survival. Yet despite the Brazil nut´s importance to the economy and the ecology of large parts of South America, very little was known about this partnership when Ortiz started his research on Brazil nut ecology 10 years ago.

Brazil nut trees are among the oldest and tallest in the Amazon, with some dating back more than 1,100 years. They grow from eastern Peru and northern Bolivia across the Brazilian Amazon. Brazil nuts are a crucial source of nutrition and livelihood for more than 400,000 Amazonians involved in their collection and sale, a business that generated more than $65 million worldwide in 1998. It´s one of the most traveled nuts in the world, and one of the last products in international trade that comes exclusively from natural forests. (Attempts to establish commercially viable Brazil nut plantations have failed.)

Where there are Brazil nuts, there are agoutis to eat them. Agoutis are smaller than their relatives the piglike pacas and larger than squirrels, which they resemble. Their large heads and bulging jaw muscles are the only hints of their power to shape the rain forest.

Agoutis are reclusive animals, and if it weren´t for the strange interconnections of biology, their crucial role in the ecology of the Amazon might still be unheralded. But Enrique Ortiz was determined to help save the Brazil nut forests in his native Peru, and that desire eventually led him to become one of the world´s leading agouti experts. At his research site at the edge of the Bahuaja-Sonene National Park, in southeastern Peru, Ortiz and his assistants use a variety of surreptitious methods for tracking the rodents and unlocking their secrets.

To get to this research site in February 1999, we traveled down the Madre de Dios River from Puerto Maldonado, the provincial capital, in a 30-foot-long canoe. It was the height of the annual Brazil nut harvest (which lasts from December to February) and therefore a good time to check on the trees´ regeneration and the agoutis´ activity. As we floated down the eddying river, Ortiz explained that, for reasons that are still not clear, this area has the highest concentration of Brazil nut trees (known locally as castañas) in all Peru. "If we´re lucky," said the 41-year-old biologist, who has a young, intense face that even a trim beard and flecks of gray don´t seem to subdue, "we´ll see an agouti."

We passed a profusion of palms, fruit trees, lofty hardwoods and cane grasses. Ortiz and his field office director at the time, Fernando "Pino" Rubio del Valle, pointed out several birds with North American relatives­­orioles and anhinga­­and an osprey, which migrates between North and South America. In the distance, a high bank of red clay appeared, and on it three lofty tree crowns. Rubio del Valle pointed them out to me and said, "There´s your first castaña!"

We turned up a narrow tributary, the Palma Real Grande, and reached the campsite as darkness was falling. We were met at the riverside by a small group of Brazil nut pickers, or castañeros, led by a man in pink-and-blue shorts. He was Fernando Cornejo, one of Peru´s leading botanists. The camp was a simple spread of thatch over a cooking area and a wooden table. The Brazil nut collectors live near Puerto Maldonado and come here during the rainy season when the trees drop their coconut-sized pods. Inside each pod, the Brazil nuts (seeds, actually) are arranged like slices in an orange.

Ortiz and Cornejo talked late into the night, discussing their work. Besides quantifying the bewildering range of life in the area, they´re also trying to get a handle on the economics of Brazil nut collection as part of Ortiz´s Castañales Project. This project, for which Cornejo is research director, works with as many as 60 Brazil-nut-picking families in an attempt to uncover ways to make the harvests more efficient, improve the workers´ livelihoods and ensure a healthier forest.

Just after dawn we got back into the boat and made for Oculto, the project´s research site. At Oculto, over a breakfast of rice and eggs, the talk turned to agoutis. "They´re hard to see," Ortiz said. "When they see you, they freeze. For a long time." To test that, Rubio del Valle and I walked up the path, macaws screeching high above us. We came to a spot where a huge tree had fallen, opening a clearing in the canopy. Four or five strands of pink flagging marked experimental plantings of seedlings, intended to bolster the forest´s natural regeneration. Around one slender plant stood a chest-high column of wire mesh.

"Against agouti," Rubio del Valle said. He explained that the pods remained in the soil beneath the very young Brazil nut plants, providing energy for the seedling and attracting hungry agoutis. So besides dispersing Brazil nut seeds, agoutis play another role: seedling predator.

We walked on and came to another massive Brazil nut trunk, at least five feet in diameter. The ground around it was littered with empty pods, most left by workers who had hacked out the nuts with a machete and hauled them off. But Rubio del Valle picked up one with a smaller hole than the others, not quite 2 inches in diameter. The hole´s edge was chiseled. "Agouti," he said.

The Brazil nut pays a price for its dependence on the agouti, losing many nuts that otherwise might sprout and replenish the ranks of Brazil nut trees. On the other hand, if agoutis didn´t liberate the nuts from the hard pod, the trees would never sprout. (So dependent are they that some biologists think the tree´s natural range may have been limited for centuries by the agouti´s inability to ford wide rivers.) In exchange for giving some of the seeds a chance, the agouti gains a prize that can see it through the lean period that comes at the end of the dry season, when other foods have rotted and gone.

 To untangle the relationship between agoutis and Brazil nuts, and its consequences for the forest, Ortiz mounted a two-year study near here, rummaging the forest for Brazil nuts that agoutis had hoarded, buried and eaten. He and several assistants even resorted to deceiving the rodents: They took apart more than 120 pods, attached a tiny magnetic strip and a number to each of the more than 3,000 seeds, and then glued all the pods back together. Weeks and months later, the researchers combed the forest with a magnetic locator to find where agoutis had eaten or stored the nuts.

Among the hazards the researchers faced were poisonous snakes and falling pods. Harvesters have been killed by the 2- to 3-pound pods falling from perches 10 stories high. Agoutis, too, have been found dead from such blows. As we walked through the forest, we came across many pods that had virtually planted themselves in their own craters. "More than once, we´ve had nuts land very, very close," Ortiz said. "Really scary. It´s like a bomb."

As we walked through one forest concession to check seedling survival, Ortiz described his findings in terms of the "agouti shadow": the outline of how far an agouti disperses an individual tree´s pods and the nuts inside. In most cases, an agouti shadow stretches about 100 feet around a tree´s base. But occasionally, through a chain of thefts by other animals from agoutis´ troves, the shadow stretches as far as 3,000 feet. That, along with human intervention, could explain how the Brazil nut´s range expanded from a small area in central Brazil to its current range throughout the Amazon basin.

Ortiz´s study also revealed the lengths to which agoutis go to hide nuts from other animals. Most of the time, agoutis store nuts in rotten logs or in the buttressed roots of strangler fig trees. But sometimes agoutis are more inventive. "We were crossing this flooded area and the magnetic locator started going crazy," Ortiz said. " Then we dipped our hands into the water and we found pods, whole fruits on the bottom under the water. It was amazing." He shook his head. "That way no one could see the nuts, no one could smell them." But the agouti knew, and came back later to retrieve its stash.

In his work as agouti detective, Ortiz has learned to identify individual animals´ trademarks. "Look at this one," he said, holding a pod with a hole shaped like a small jack-o´-lantern´s smile. "Every agouti has a signature. You find some holes are oval-shaped, some are star-shaped, some are heart-shaped." Like a criminal with a telltale modus operandi, an agouti will open nuts with the same kind of hole every time, at the same point on the pod.

An agouti´s burying activity is designed to ensure its survival through a lean season, but it also helps other animals. Peccaries, for example, search the agoutis´ haunts for the protein-rich nuts, digging into the dirt around fallen logs on the chance of finding a horde. Eight other species, including pacas, pacaranas, spiny rats and porcupines, also steal Brazil nuts stored by agoutis. In addition, several frog species owe their survival to the agouti-Brazil nut relationship. Researchers in Brazil found that the poison arrow frog, for one, relies almost exclusively on rain-filled Brazil nut pods for water to get through the tadpole stage.

I stopped on the path to catch my breath. Ortiz reminded me that castañeros walk this path with 150-pound loads of nuts on their backs. Sometimes they carry the loads as long as two hours to a boat landing. From there, the nuts are as good as money: Castañeros can trade sacks of nuts for everything from canned goods to medical treatment. The profit margin of the Brazil nut harvesters, however, remains cloudy. For that reason the project is keeping careful records to see how much a natural forest repays collectors, who work concessions­­averaging 2,500 acres each­­granted by the government. These records can show hard-nosed loan officers that a family´s Brazil nut concession is at least as good an investment as a cattle farm. Not to mention a much better investment in biodiversity.

Where castañeros manage a forest concession for Brazil nuts, there is a legal and economic basis for protecting the area from destructive land uses such as cattle ranching and mining. The Castañales Project and other environmental groups have convinced the government to lengthen the concession periods from two years to five. Longer time frames give collectors a stable basis for their enterprise and incentive to manage their area with an eye for its long-term health­­for example, protecting seedlings to help natural regeneration.

After a brief rest, we moved on through the forest, but failed to spot an agouti on our hike. We spent the next day at another part of the concession, where the path was overgrown and the machete rang like a bell against the lianas. No agouti sighting.

My last day in the forest, in a final bid to glimpse one, I walked up the path at dawn and again at twilight, when agoutis are most active. I kept still and focused on watching. Fifteen minutes passed, then thirty. As daylight faded, fireflies started to spark high above in the canopy. Suddenly I heard a noise nearby.

It was Ortiz, coming down the path. Dispirited, I complained that I´d waited in vain for agoutis. "They are secretive. People rarely see them," he said consolingly.

But the agoutis´ handiwork was clear, he claimed. Castañeros may view the empty pods as a lost harvest, but they are also a sign of a forest replenishing itself. "Without the agouti," he said, "this forest would be very different. The Brazil nut is the dominant tree here, and it depends almost exclusively on the agouti. To a great extent, they´re responsible for what this forest looks like."

David Taylor is a free-lance writer based outside Washington, D.C. He writes about people, culture and the environment.

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