Amphibians in Brazil’s Pantanal, one of the world’s largest and most biodiverse wetlands, could lose huge swaths of their habitat as the region dries out from climate change, a new study has found.

Researchers studied the Upper Paraguay River Basin (UPRB), which stretches into parts of Paraguay and Bolivia and fully contains the Pantanal. Of the 74 known species of frogs and other amphibians that live there, 84% would lose at least part of their current range by 2100 under a moderate climate change scenario, the climate models run by the researchers showed.

“I imagined we might see a reduction in species, with longer dry seasons already affecting the Pantanal,” Matheus Neves, the study’s lead author and a Ph.D. researcher at Brazil’s Federal University of Mato Grosso, told Mongabay by phone. “And amphibians, which mostly depend on water, are particularly vulnerable.”

Among them is the tiny, 4-centimeter (1.6-inch) Cuyaba dwarf frog (Physalaemus nattereri), which defends itself by ballooning its rear end to reveal large fake eyes and scare potential predators away. It can also squirt poison out of those fake eyes.

The frog is projected to lose more than 300,000 hectares (741,000 acres), or 85%, of its UPRB range by 2100 under the moderate emissions scenario.

Thirteen of the 74 species identified could lose 100% of their range in the basin under the same scenario. Under a high-emissions climate scenario, where only minimal climate action is taken, that number increases to 20 species.

Extinction isn’t likely, as these amphibians are also found outside the Pantanal biome. But Neves said their decline signals trouble for the wetland.

“Everything depends on amphibians,” he said. “If you reduce amphibians, you reduce food for seed-dispersing animals and you lose control over populations that amphibians keep in check, like mosquitoes, spiders and pests.”

Currently, less than 6% of the UPRB lies within protected areas, leaving most of the biome without long-term safeguards against wildfires and deforestation.

While the Pantanal evolved with fire, Neves said, wildfires have become more widespread and intense over the last five years. In 2024, fires scorched more than 15% of the wetlands during a record-breaking drought.

The authors write that to protect amphibians in these wetlands, expanding conservation areas is key. Their analysis highlights priority zones where species are likely to seek refuge, including the highlands of Serra de Maracaju, near Brazil’s border with Paraguay, to help guide policy.

Brazil is a signatory to a 2022 United Nations biodiversity agreement whose goal is to protect 30% of the planet’s land by 2030, a target the authors say offers hope for the Pantanal and its threatened amphibians.

“We analyzed how much of each species’ distribution is currently protected. If we expand to 30%, we could protect the majority of [the amphibians],” Neves said.

Banner image: The Cuyaba dwarf frog (Physalaemus nattereri) inflating its rear end to scare away predators. Image courtesy of Felipe Bittioli.