In a region of wetlands in central Brazil, leopard jaguars spend their days wading in deep chest waters in search of fish. When not hunting, the big cats playfully wrestle with each other on the ground. Their lives are unlike any other known jaguar existence in the world.
The new findings reveal a degree of flexibility in diet and lifestyle unprecedented among jaguars. The discovery may provide a key context for the role of cats in food webs, helping scientists better understand the impact of environmental changes on the species, researchers reported October 6. Ecology.
Jaguar (Panthera onca), which are usually solitary in the territory and hunt on the ground, and inhabit a wide range of habitats, ranging from the deserts of North America to the grasslands and tropical rainforests of Central and South America. Cats are also found in the Pantanal, an enormous tropical wetland – the largest of its kind in the world – that stretches over parts of Brazil, Bolivia, and Paraguay.
Ecologists Manuel dos Santos-Filho of the Universidad do Estado de Mato Grosso in Cáceres, Brazil, and Carlos Perez of the University of East Anglia in Norwich, England, rumors of large numbers of jaguars have appeared near the Tayama Ecological Station in Brazil. This large ecological reserve is located in the remote northern regions of the Pantanal.
After relaying these tales to Tal Levy, a wildlife ecologist at Oregon State University in Corvallis, the researchers began a project to better understand the jaguar’s biology and population status in the protected area.
Taiamã is flooded seasonally, with no roads or trails, so the team had to reach the reserve by boat, and set up motion-activated cameras along the waterways to collect data on jaguar numbers. However, the region’s abundance of jaguars was immediately apparent.
“You put your foot out of the boat, and there’s already a trail of a Jaguar,” says Charlotte Erickson, a wildlife scientist at Oregon State University, too. “There are scratches on the trees. There are jaguar remains. There is just an incredible presence of this primate predator wherever I go, something I’ve never seen anywhere before,” says Erickson.
The team published 59 cameras, running from 2014 to 2018, and collected more than 1,500 Jaguar videos. The researchers also captured 13 jaguars and fitted them with GPS or radio collars to gain insight into the animals’ population density, movements and social interactions.
Based on their data, Erickson and colleagues estimate that the Taiyama Ecological Station hosts the highest density of jaguars ever recorded: 12.4 animals per 100 square kilometers, nearly three times some of the following highest estimates elsewhere. Jaguars were also the most common mammal spotted on cameras.
Video footage showed the tigers carrying a large fish. When the team analyzed 138 stool samples, the researchers found that 55 percent of them contained fish remains and 46 percent contained aquatic reptiles, such as caimans or turtles. Only 11 percent contain mammal remains.
Well-documented jaguars stand up to challenging prey, including underwater fare (SN: 15/7/16). Erickson and her team believe that Taiyama felines not only have the most fish-based diet among tigers, but also of all the big cats. Researchers say there are tigers in Bangladesh that live in flooded mangrove forests and occasionally eat fish, but those cats still eat food primarily from land.
Cameras and tracking collars also showed that the Taiamã riders were spending a lot of time close to each other, sometimes traveling, hunting and playing together. This is all very strange behavior for jaguars, at least based on what scientists know about cats elsewhere in the world.
Regarding social behavior, “What we knew about tigers prior to this study was that they are basically solitary, and meet to mate. That’s it,” says Erickson, pointing to tales of cats sharing prey carcasses as rare counter-examples.
The abundance of aquatic prey in the submerged reserve – protected from human encroachment – may be responsible for the jaguar’s extreme density and rich social life. It’s possible, says Erickson, that there is so much food available that “there is no real need to fight for it.”
Another idea, Levy says, is that aquatic prey concentrated along the edges of the river can only be reached in certain areas. This may encourage jaguars to molt, since access to multiple hunting grounds requires compatibility with other jaguars. Other animals behave in similar ways. Levy says brown bears, for example, congregate in large numbers to feed in salmon breeding grounds, despite the bears’ solitary nature.
Tigers’ abundance and social behavior are not surprising, given the available food resources, says Todd Fuller, a conservation biologist at the University of Massachusetts Amherst. However, he finds the new information exciting.
Fuller, who was not involved in the research, says the study helps bring researchers’ understanding of jaguar ecology and conservation closer to what is known about most other big cat species, and “that’s a very good thing.”
The Jaguar Pantanal faces many threats and is retreating within Brazil, says Erickson, suffering from drought, fires and agricultural expansion. Assessing how Jaguar responds to such changes is critical. In 2020, half of the study area was burned, so Erickson is currently evaluating the impact of the fires on jaguars and their submerged home periodically.
She also wants to investigate how the taste of Taiamã jaguars affects how often animals eat their land-dwelling prey and what strategies cats use to catch fish.
“We think we know a lot about these attractive, large predators,” she says, “but there are still things to learn.”