Revolt of the capybaras: Have these large rodents taken over — or reclaimed what's theirs?

Has social revolution spread to Argentina? While the country has historically witnessed economic strife, onlookers were graced with a new sort of rebellion in 2021, when hordes of capybara (large rodents also known as “water hogs”) created a stampede and rampaged through gated communities in an affluent suburb located twenty five miles north of Buenos Aires. Known in Argentina as carpinchos, capybaras are gentle and herbivorous, but they are hard to miss. They are the world’s largest living rodents, measuring more than three feet long and weighing more than 170 pounds.

Though previously preyed upon by jaguars, the latter have almost disappeared in Argentina, and now the rodents, which reproduce at a high rate, as many rodents do, have increased in population. Local scientists say that in one year, their numbers shot up by 16%, according to Time Magazine. More and more have been trampling through gardens and golf courses.

Recently, capybaras have expanded their presence in Buenos Aires province due to climate change. Indeed, the capital has become more tropical, and increased temperatures and precipitation have created more suitable habitat for the creatures. Researchers believe more rainfall and flooding may have caused some brackish lagoons to become less salty, a trend which favors capybaras, since the animals are semi-aquatic freshwater mammals. They seemingly prefer water so much, “hydro” is in their Latin binomial twice: Hydrochoerus hydrochaeris.

The rich label the rodents “pests,” but are these “masters of the grasses” invaders or merely “reappropriating” what is theirs? Gated communities and golf courses are located on vulnerable wetlands along the Paraná River, home to capybara habitat. However, this hasn’t stopped rapacious real estate interests from pursuing indiscriminate development which poses a threat to wetlands. Leftist politicians, meanwhile, argue capybaras have become a “symbol of socio-environmental resistance” and even call for “capybara protest caravans.” Young environmentalists, meanwhile, have created a popular hashtag, "VidaDeCarpinchos" (“Life of Carpinchos”) to draw attention to ongoing environmental campaigns.

Activists are particularly concerned about wetland ecosystems, which are vulnerable to climate change. Ominously, the Paraná delta — the second largest river in South America after the Amazon — caught fire several years ago amid terrible drought. The flames worsened when the water table dropped, which in turn exposed flammable carbon-rich soil. Paradoxically, even though climate change has benefited capybaras in certain respects, in other ways the animals have been placed at greater risk. Indeed, wildfires displace capybara, driving them towards urban areas, and drought may drive the animals to flee towards areas with already scarce water resources.

A capybara crosses a street while others eat grass in a gated community in Tigre, Buenos Aires province, on August 27, 2021. (MAGALI CERVANTES/AFP via Getty Images)Though rodents have evolved in South America for millions of years, some may wonder how the animals will cope with new environmental challenges. Such vexing questions would have intrigued naturalist Charles Darwin, who made his way through South America from 1832 to 1835. During his travels, Darwin took in local wildlife, including rodents, and his observations later informed the theory of evolution. Traveling along the Paraná, Darwin observed thickets which “afford a retreat for capybaras and jaguars. The fear of the latter animal quite destroyed all pleasure in scrambling through the woods.”

When he wasn’t eating sleek brown rodents himself — probably the twenty pound agouti, which Darwin regarded as “the very best meat I ever tasted” — or collecting small tuco-tuco rodents as pets, the naturalist made important rodent fossil discoveries in Argentina. For instance, he uncovered specimens which were different, but related to, the living Patagonian mara, a sort of rabbit-like creature. Other specimens belonged to an extinct species of tuco-tuco which grew as large as current-day capybaras. Though it’s unclear whether Darwin’s “cavia” fossils provided a critical “a-ha” moment, some believe the discoveries contributed to evolutionary theory, since they proved direct descent of species living in the same area. 

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Despite their long and enduring evolutionary journey, rodents in Argentina, including capybara, face ecological stress in wetlands, while their smaller cousins are hunted and regarded as critically endangered. Take, for example, the Chalchalero Vizcacha rat, whose range has been reduced to less than five square miles. Then there’s the tuco-tuco, which Darwin described on his travels as “A curious, small animal…tucotucos appear…to be gregarious…This animal is universally known by a very peculiar noise…A person the first time he hears it is much surprised.” While some tuco-tucos have managed to survive for thousands of years while enduring harsh climatic conditions, rodent habitat has now been cleared for agricultural and industrial use.

Retracing Darwin’s route, I’ve come to Buenos Aires in conjunction with a book project examining the naturalist’s legacy in relation to climate change. At the Bernardino Rivadavia Argentine Museum of Natural Sciences, I caught up with paleontologist Agustín Martinelli. Though capybaras were certainly affected by recent fires and are sometimes hunted, the scientist explains the animals are still abundant in certain areas.

Indeed, capybaras are hardly endangered, and the creatures, which form part of the larger caviomorph group, are hardy survivors. Rafting from Africa to South America 40 million years ago across an Atlantic that was then more narrow — a voyage which took just one to two weeks — caviomorphs subsequently underwent an “incredible evolutionary radiation.”

Because South America was then an island and had split from North America, there was little competition from other mammals, which allowed rodents of all sizes to evolve with little pressure. The earliest caviomorphs, which arrived during the Mid-Eocene Climatic Optimum, a period of elevated temperatures, were tiny, but Martinelli remarks there’s evidence of other extinct giant rodents in the fossil record. In neighboring Uruguay 2 million years ago, one rodent grew to one ton in weight.

However, once North America rejoined South America, other animals such as saber-toothed cats crossed the land bridge, which may have brought about the demise of giant rodents. It's also possible that changing climate, which switched from lush to arid-like conditions, may have made giant rodent habitat less hospitable for the creatures. But the current day capybara survived.

Not all giants vanished, however: glancing atop a shelf in Martinelli’s office, I spotted a model of Toxodon, a nine foot long hoofed creature which weighed one ton and looked like an “evolutionary Frankenstein” combining hippo, rhino and rodent-like features. In 1832, Darwin uncovered molar teeth belonging to Toxodon, and the following year he discovered a skull belonging to the creature in Uruguay. Though Toxodon went extinct more than 11,000 years ago, the animal overlapped with humans in South America. Toxodon, Darwin wrote, was “perhaps one of the strangest animals ever discovered…the structure of its teeth…proves indisputably that it was intimately related to the Gnawers [rodents].”

Though Darwin wondered about the relationship between capybaras and Toxodon, we now know the latter wasn’t technically a rodent but rather belonged to a larger extinct group of animals called notoungulates. During the Pleistocene, Toxodon may have been the most common hoofed mammal in South America, and Darwin was “deeply astonished” at the disappearance of such “great monsters.” Though he did not believe changes in temperature provided the death blow, researchers now believe climate could have played a role, or perhaps human hunters contributed to Toxodon’s demise.

Montevideo, where I also plan to speak with scientists, is a short ferry ride from Buenos Aires. When he wasn’t examining extinct rodent-like skulls in Uruguay, Darwin remarked on “ludicrous” looking capybara making “peculiar” grunts. The animals, he remarked, “were very tame,” which he attributed to “the jaguar having been banished for some years.”

At a storehouse belonging to Uruguay’s National Museum of Natural History, I met with paleontologists Andrés Rinderknecht and Washington Jones. Shortly before my arrival, the museum had put on an exhibit dealing with Darwin’s legacy in Uruguay. The naturalist’s discovery of Toxodon fossils in Uruguay, Rinderknecht remarked, was an important step which helped Darwin come up with evolutionary theory. Jones added that when the museum launched its exhibit, they had been careful to include a replica of Darwin’s Toxodon skull and jaw.

The conversation turns to the plight of capybaras once more. Though it’s illegal to hunt the creatures in Uruguay, some still disobey the law. Despite this, Rinderknecht says it’s remarkable how these “clumsy” yet “incredible” animals have managed to endure. When jaguar predators disappeared, capybaras were left alone to reproduce. Yet when asked about the environmental catastrophe on the Paraná River which has affected the animals, the scientist weighs his words carefully.

“Capybaras aren’t threatened,” he remarks, adding with emphasis, “for now.” 

Though giant rodents, not to mention huge “rodent-like” mammals, have long since disappeared from South America after succumbing to climatic changes, and perhaps even human encroachment, capybaras and other smaller rodents are still with us. Remarkable survivors, they have similarly endured climatic changes throughout their evolutionary history, yet some may wonder whether they have now finally met their match.