Oregon State University researchers and a team of international scientists have gained new insights into the diet, population density and social interactions of a group of Brazilian jaguars.
Fish and aquatic reptiles dominated the diet of jaguars in a remote wetland area in Brazil and constituted the first jaguar population known to have minimal mammalian diets. In addition, motion-controlled video cameras showed jaguars playing, fishing and traveling together.
The findings, recently published in the journal Ecology, contradict the belief that jaguars are solitary mammals whose social interactions are limited to courting or arguing over territory, said Charlotte Eriksson, a graduate student at Oregon State and lead author of the article.
The research took place in a seasonally flooded protected area in the northern part of the Brazilian Pantanal, the largest freshwater wetland in the world. Fishing is prohibited in the area. There are no roads or settlements nearby, and livestock is not allowed.
The flooded nature of the region and the fact that the researchers have to cover themselves from head to toe because of the many bites make it a demanding place to work.
âEverything is boat based,â said Eriksson. âOf course we can’t drive. And we can’t really walk because there is water and lots of jaguars. “
Taal Levi, associate professor at Oregon State, initiated the project in 2014 in collaboration with Brazilian researchers in the area after Carlos Peres, professor at the University of East Anglia in the UK, described a place with an unusually high jaguar population density.
Eriksson is a member of Levi’s laboratory. As part of her doctoral thesis, she started working on the project in 2017. Since then she has visited the Brazilian site twice, in 2018 and for six weeks in August and September of this year.
For the just published paper, the researchers also collected jaguar scat. They identified nine prey items in 138 kots. The jaguar diet was dominated by three groups: reptiles (55%), fish (46%) and mammals (11%).
This result shows that jaguars in this region have by far the most aquatic diet and lowest mammal consumption of any previously studied jaguars, the researchers said. Even tigers in the Sundarbans mangrove forest in India, which may be the most comparable large cat family in a similar habitat to the jaguars in the Brazilian region, primarily consume landbound mammals.
The researchers also caught and fitted GPS collars to 13 jaguars that spent an average of 96% of their time in the study area. They estimated the jaguar density at 12.4 per 100 square kilometers, or 36 square miles. This density is two to three times higher than what other scientists have found for jaguars in other regions of South America.
The researchers believe the density is so high and the jaguars are interacting in unprecedented ways due to the abundance and distribution of aquatic prey they call aquatic subsidies in the area. In other words, their biological needs are met so that they have energy to burn or play with.
“When there is a lot to eat, there is less arguing about it,” said Eriksson.
The researchers used data from 59 camera stations that were in operation for 8,065 days from 2014 to 2018. Jaguars were detected on 95% of the cameras. A total of 1,594 videos of jaguars were received, depicting 69 unique individual animals. The maximum number of unique jaguars captured by a camera was 15, including nine in 2015 alone.
“Usually you rarely see a top predator on camera because they move over very large areas,” said Eriksson. “Jaguars were the most common mammal seen on camera – which is really unusual.”
Researchers documented 80 independent social interactions between adult jaguars. Of these, 85% were between men and women, but 12 were between same-sex jaguars (one woman-to-woman interaction and 11 man-to-man). Two men even spent 30 minutes in front of the camera playing.
Other authors on the paper include Levi and Joel Ruprecht, both from the Oregon State Department of Fisheries, Wildlife and Conservation Sciences at the College of Agricultural Sciences; Daniel Kantek, Selma Miyazaki and Ronaldo G. Morato from the Brazilian Instituto Chico Mendes de ConservaÃ§Ã£o da Biodiversidade; Manoel dos Santos-Filho from the Universidade do Estado de Mato Grosso, Brazil; and Peres.