Recently, researchers discovered that jaguars in Brazil’s Pantanal—the largest freshwater wetland in the world—have the most aquatic diet of any previously studied population of jaguars. ©Helder Brandao de Oliveira

At more than 81,000 square miles—greater than 10 times the size of Florida’s Everglades—the Pantanal, located mostly in Brazil, is the largest tropical wetland and one of the most pristine in the world. This seasonally flooded plain is fed by tributaries of the Paraguay River and is one of the planet’s most productive habitats.

Here, annual floods, fed by tropical rains, create a giant nursery for aquatic life, including 260 species of fish. As the waters recede in the dry season, the Pantanal attracts sizable numbers of birds and other animals—such as giant river otters, marsh deer and tapirs. It also holds dense populations of an elusive and little-known big cat: the jaguar.

On the International Conservation of Nature’s Red List, jaguars (Panthera onca) are classified globally as near threatened—the only species in the big cat genus Panthera that’s not in one of the threatened categories. In Brazil, however, jaguars are considered a vulnerable species. Their global population is estimated to be 173,000 individuals, with Brazil home to around 86,000. In the Pantanal alone, there are thought to be 4,000 jaguars.

In Brazil’s Pantanal, fishing is prohibited, there are no nearby human settlements and cattle ranching is not allowed. ©Helder Brandao de Oliveira

Researchers have long thought that jaguars are solitary mammals whose social interactions are limited to courting or disputes over territory. But a new study, conducted by researchers at Oregon State University, is turning that notion on its head.

On-camera cats

Jaguars are able to live in a wide array of habitats, ranging from North American deserts and grasslands to tropical rain forests in Central and South America. But when researchers in Brazil heard rumors that a large number of the cats had been sighted near the country’s Taiama Ecological Station, a vast, 28,553-acre reserve located in the remote, northern reaches of the Pantanal, they began a joint project with Oregon State University scientists with the purpose of better understanding jaguar biology and population status in the protected area.

The Taiama Ecological Station was created in 1981 in a section of the Pantanal where the wetland begins, with floodwaters spreading out from the Paraguay River’s channels. The river borders the reserve in the south, and a water channel called the Bracinho edges it in the north. On the other side of the Bracinho lies another conservation unit, the 87,800-acre Jurban Private Natural Heritage Reserve. This terrain’s characteristics helped to prevent the occupation of the area and guarantee its isolation, and the variation in water levels in the conservation unit allows the jaguars to live there during both the wet and dry seasons.

The Pantanal hosts one of the largest populations of giant otters in South America. They are listed as endangered by the International Union for Conservation of Nature. ©Helder Brandao de Oliveira

With no roads or trails in the reserve, the scientific team had to access the protected area by boat, setting up motion-activated cameras along waterways in the hopes of gathering data on jaguar numbers. Evidence of a bounty of the big cats in the area became immediately obvious; there were jaguar footprints, jaguar scratches on trees and jaguar scats.

A total of 59 cameras were deployed, which operated from 2014 to 2018. They collected almost 1,600 videos. Surprisingly, jaguars were detected on a full 95 percent of the cameras and were the most common mammal spotted in the videos. Typically, apex predators are seen very infrequently on camera because they move over very large areas.

In all, 69 different jaguars were identified in the videos. The maximum number of unique jaguars captured by any one camera was 15.

Once heavily hunted for its valuable skin but now protected, the yacare caiman is found in large numbers within the Brazilian Pantanal. ©Wendy Klausner

The researchers also physically captured 13 jaguars and fitted them with GPS or radio-tracking collars to gain insights into the cats’ population density, movements and social interactions.

GPS jaguars

Not only was the number of jaguars seen on the videos astounding, but what the facts revealed about their everyday lives was astonishing. The videos showed that in these central Brazilian wetlands, jaguars spend a large part of their days wading through chest-deep waters searching for fish. When not hunting and back on land, the big cats playfully grapple with each other. Two males even spent 30 minutes in front of a camera rolling around together, play fighting and exchanging soft bites. Such day-to-day activities disclose a degree of flexibility in diet and lifestyle previously unseen among jaguars anywhere else in the world.

Based on their data, the researchers estimate that the Taiama Ecological Station hosts the highest density of jaguars ever recorded: 12.4 animals per 38 square miles, nearly triple what other scientists have found for jaguars in other regions of South America. They were able to document 80 social interactions between adult jaguars. Of those, 85 percent were between males and females, but 12 were between same-sex jaguars (one female-to-female interaction and 11 male-to-male encounters).

Capybaras are large, semiaquatic rodents that inhabit the waterlogged regions of Central and South America. Like beavers, they are strong swimmers. ©Holly Glessner

The video footage showed jaguars carrying off large fish; and, indeed, after 138 scat samples were analyzed, 55 percent of them were found to contain aquatic reptiles, such as caimans (small crocodilians) or turtles, and 46 percent had fish remains in them. Just 11 percent contained mammal remains, mostly capybaras. This makes the Pantanal jaguars the first population of jaguars that are known to feed minimally on mammals.

Previously, jaguars had been well documented taking on challenging prey, including underwater fare. But these Pantanal felines may not only have the most fish-dependent diet among jaguars, but also among all big cats. There are tigers in the Sundarbans Reserve Forest, located in the southwest of Bangladesh, that live in flooded mangrove forests and that sometimes eat fish; but, say the researchers, those cats still primarily eat land-based food.

From the 13 jaguars that were fitted with GPS or radio-tracking collars, the researchers gleaned more insights into the lives of the Taiama Ecological Station cats. The data showed that, on average, they spent 96 percent of their time in the reserve and most of their hours near each other; often fishing, playing and traveling together. This is exceptionally odd behavior for jaguars, at least based on what scientists know about the felines elsewhere in the world.

Jaguars are the third biggest cats in the world, after lions and tigers, and they are the largest cats in the Americas. Sadly, their range has decreased by half in the last 100 years due to human activities. ©Helder Brandao de Oliveira

Fishing—and future—felines

The researchers postulate that the superlative density and rich social lives of the Pantanal jaguars may be the result of the profusion of aquatic prey in a flooded preserve that is protected from human encroachment. It could be that there’s so much food available here that the big cats have no need to fight over it.

Another theory is that aquatic prey concentrated along the river margins are accessible in only certain areas. This may encourage jaguar territories to dissolve, since obtaining access to multiple fishing spots requires getting along with other jaguars. Other animals behave in similar ways, such as the brown bears in Alaska and British Columbia that congregate in great numbers to feed at salmon spawning grounds, despite the bears’ typical solitary natures.

As one of the largest predators in South America, jaguars are often seen as a litmus test for forest health. Unfortunately, jaguars face many threats and are declining within Brazil, suffering from agricultural expansion and deforestation, climate change, droughts, fires, hydroelectric plants, mining, “revenge hunting” by ranchers who kill jaguars thought to be preying on their livestock and the illegal wildlife trade, which targets them for their skins and body parts.

The Pantanal is known throughout the world for having some of the planet’s most beautiful and colorful sunsets. It’s a magical place, full of some very special, bewitching big cats. ©Eric Rock

Evaluating how well jaguars are responding to such threats is paramount. In 2020, for example, half of the study area burned, so assessing the impact of the fires on the jaguars and their periodically submerged home could provide context on the cats’ role in food webs.

It’s clear we have a lot to learn about the animals we think we might already know, such as jaguars. But continuing to gather knowledge about how these big cats live and how adept they are at adapting to changes in the world’s largest freshwater wetland—one of the Southern Hemisphere’s greatest natural phenomena—could be paramount in helping to protect them into the future.

Here’s to finding your true places and natural habitats,