- Known in Brazil as the admirable little red-bellied toad, the rare Melanophryniscus admirabilis is endemic to a stretch of the Forqueta River in Rio Grande do Sul state. It made history in 2014 when it halted the construction of a hydroelectric dam that would have destroyed its only habitat.
- After the 2024 floods, researchers returned to the area to assess the impacts of the state’s biggest climate catastrophe on its environment.
- With just over a thousand individuals in the wild, the species is listed as “critically endangered”; in addition to climate change, the little toad suffers from the advance of monocultures and the threat of wildlife trafficking.
ARVOREZINHA, Rio Grande do Sul, Brazil — The admirable little red-bellied toad is the size of a thumb, but it has achieved giant feats: In 2014, it prevented the construction of a small hydroelectric dam that threatened to alter its only habitat forever. Endemic to a small stretch of the Forqueta River, in the municipality of Arvorezinha, Rio Grande do Sul, Melanophryniscus admirabilis is one of the rarest and most threatened species on the planet. Recently, after the floods that devastated the state in 2024, researchers returned to this refuge to assess whether the little toad that once halted the construction of a dam has survived the force of the waters.
In October 2025, almost a year and a half after the biggest climate disaster in Rio Grande do Sul, I joined a team of researchers that would document what remained of the small habitat where just over a thousand little red-bellied toads used to live. The destination was Perau de Janeiro, a hidden fold of rocks and humid forest. Seen from above, the place, which is surrounded by tobacco plantations and pastures, looks like a common forest scene. But as we go down a steep trail, the atmosphere changes immediately. The smell of moss, the shining wet outcrop, the sound of the powerful flow of the river that ends in a waterfall: It was there that the little toad halted progress. And it was there where we wanted to find out if it still vocalized.
Described by science in 2006, the little toad belongs to the Bufonidae family, and, despite being able to jump, it prefers to walk slowly as if measuring the ground before taking each step. Its green back and its little colorful legs and belly form an unlikely contrast for someone who prefers not to be seen but insists on being remembered. These warning colors serve as an alert to visually oriented predators that the animal is toxic, dangerous or unpalatable — a defense mechanism known as aposematism.
The eyes that observe them quickly jump to the light green dots that form patterns on the bottom of their abdominal area. “I say that when we observe these little spots, they are like constellations. So we can see some patterns, as if we were looking at the stars,” says Michelle Abadie, a biologist and the leader of the research team, comparing the toad’s macroglands to dots in the sky. The glands release toxins as a defense mechanism but also serve as individual identification similar to a human fingerprint.
Abadie has been working with the species for 15 years, and since the beginning of her research, she has faced challenges when it comes to keeping the toad population stable. In August 2010, the local environmental agency granted a preliminary license for the construction of a small hydroelectric plant on the Forqueta River. Such plants often cause drastic changes in river flows, block the circulation of species that depend on water and eliminate natural variations in water level that sustain entire ecosystems. For the M. admirabilis, whose reproduction depends on rainfall patterns and the formation of ephemeral puddles, the dam would be a death sentence.
Therefore, the researchers decided to coordinate their actions. With the information collected during fieldwork, Abadie and her colleagues were able to assess the extinction risk of the species’ only known population. In 2013, the little toad was listed as “critically endangered” on state, national and global lists of threatened species. Their joint efforts with other research institutions led Brazil’s Federal Prosecution Service to embargo the construction works in 2014. “The dam would be built less than 300 meters [980 feet] from the toad’s habitat. Any change there would’ve been the end,” she recalls. This was the first documented case in Brazil — and, to our knowledge, in the world — in which an amphibian managed to halt a project of such magnitude.
The effects of floods
According to a study conducted by the National Water and Basic Sanitation Agency (ANA, for its Portuguese acronym), southern Brazil is the region with the highest projected increase in floods in the coming years, where maximum river flows could grow by about 20% and extreme floods could become up to five times more frequent. The 2024 floods were the most dramatic example of this trend, having affected approximately 2.4 million people in 478 municipalities.
On that occasion, the Forqueta River rose and swallowed its own course. The rocks and the outcrop disappeared. No one knew if the little toad still existed. While Abadie remained isolated in her city, information about the Perau de Janeiro came from local resident Graziela “Grazi” Civa, a key partner of the project.
Civa’s family leases the property where the little toad also lives, and she is now considered something of a guardian to the animal. Both she and the surrounding rural community say they had never witnessed rainfall like what they saw in 2024. “The landscape changed so much that it didn’t even look like the same place,” she recalls, pointing to where the river stamped the tree that witnessed it all: During the floods, the Forqueta River rose by at least 20 m (65 ft).
This first expedition after the disaster expected to find admirable little toads alive and in the same places they usually occupied. But they were concerned that the force of the water might have changed the spatial dynamics of the place, uprooted the vegetation and dragged adult individuals, tadpoles and eggs far away.
While the river is more than 150 kilometers (93 mi) long, only one stretch of outcrop offers the ideal conditions for this species to live and reproduce, so much so that it has never been found anywhere else. “We looked for places similar to this while doing sampling, but we didn’t find the same pattern: rocky outcrop and valley fitted with forest that maintains moisture and allows for ephemeral puddles,” Abadie says.
In the field with the admirable
Three other biologists joined Abadie in fieldwork: Debora Bordignon, Karoline Zenato and Jaqueline Becker, all members of the Herpetology Laboratory at the Federal University of Rio Grande do Sul. Each researcher’s backpack had rubber boots, gloves and plastic bags for sample collection, clipboard, pens and a camera for recording everything, in addition to sandwiches and water for a whole day away from the base.
Once near the banks of the Forqueta River, every caution was necessary to avoid trampling any individual, as the little toads tend to hide in the vegetation adjacent to the river. Bordignon says that during the reproduction period, males descend from the hill to the rocky outcrop near the river and call up the females, who then go to meet them in order to start mating. We arrive there already facing quadrant 24, where the researchers indicated that there was a higher concentration of individuals. Since the beginning of the research, the project has divided the sampled stretch into 31 15-square-meter (160-square-foot) quadrat transects.
“I found it!” Zenato announces, after searching for a long time in a small leaf-covered crevice carved into the rock. It was a female. I ask if it was already possible to know if this was a new individual or a recapture, to which Abadie replies that this would only be done later, in field reports. Based on photographic records illustrating belly spot patterns, they use software that has been part of the project’s database since 2010 to examine the images. This methodology enables them to compare the photographs and estimate population size year after year.
The admirable little toad has an explosive reproductive strategy in which most individuals mate simultaneously under specific climate conditions: heavy rains, followed by periods of sunshine that warm up the temporary puddles. “The best time for us to find the species in its mating activity is between late August and early December, on days with temperatures ranging from 15-30° Celsius,” or 59-86° Fahrenheit, Abadie says.
After hours capturing isolated specimens, we finally manage to document tadpoles, and soon after that, two individuals performing the nuptial embrace known as amplexus. Sometimes, other competing males may remain around, disturbing the couple and trying to copulate with the female. They are called displacer males.
In two days of sampling, the team found 111 individuals, including adults and juveniles. “They are reproducing, which means the cycle has been maintained,” Abadie explains. “This is not our highest number ever, but it’s reasonable. The vegetation is recovering, so it’s returning to the micro-habitat that we know. But quadrat 24 is apparently no longer the favorite place for the little toads.”
What has become of the little toad?
Despite these initial observations, many questions remain unanswered, and a single expedition is not enough to understand the full complexity of the species at this time. Therefore, the admirable little toad was one of the species included in Brazil’s National Action Plan for the Conservation of Threatened Species coordinated by the Chico Mendes Institute for Biodiversity Conservation.
This was the initial phase of a three-year post-disaster monitoring project based on predictive research data and the same methodology that has been used since 2010, which enables researchers to estimate this unique population’s size and survival rates.
Climate change may be one of the main threats to the admirable little toad, but not the only one. Tobacco, soy and eucalyptus plantations are associated with deforestation in the region where the species occurs. In 2018, the place was recognized as a Key Biodiversity Area (KBA) and a Alliance for Zero Extinction (AZE) site, but no formal conservation unit has been established so far.
In conservation planning, KBA and AZE data sets can be used to guide the creation of protected areas. But the only place where the species is found is a private property with scenic landscapes and a waterfall, which is used as a local tourist attraction. Therefore, sustainable economic activities are preferable in the surroundings.
The Federal University of Rio Grande do Sul, through its Herpetology Laboratory, has conducted research as well as actions that go beyond academic activities. The goal is to build bridges with the community, bringing conservation closer to people, especially local schools, and also act in the political field.
Together with State Representative Matheus Gomes, who introduced bill 119/2024, researchers dream of recognizing the admirable little toad as genetic heritage of Rio Grande do Sul. Much more than a legislative proposal, the idea is an invitation for society, companies, governments and institutions to rethink their relationship with biodiversity. If the bill is passed by the state legislature, the toad, whose colors are the same as the state’s flag, might become a symbol of hope and learning, a reminder that conservation also means a deep connection with our roots.
While the colors of the little toad can be a powerful tool to draw attention to conservation, this very characteristic may also be a threat. Its striking appearance may increase its vulnerability and therefore its risk of extinction. Traffickers and collectors seek exotic specimens for their rarity and striking beauty, fueling illegal wildlife trade.
While the species has not yet been documented in the pet trade, almost 450 amphibians have been found in the global chain. According to data, wildlife trafficking is one of the main factors threatening vertebrates’ survival worldwide, affecting about 25% of all terrestrial species.
Every step, whether during field work, at the laboratory or within the government or legislative sphere, reveals the resilience of an almost invisible world that insists on surviving. A small species is strong enough to remind us that, when it comes to conservation, tiny things are no less important. This story may have been like a mirror that reveals our mistakes but also our possibilities for change.
Banner image: The admirable little red-bellied toad (Melanophryniscus admirabilis). Image by Thamys Trindade.
This article was first published here in Portuguese on Dec. 8, 2025.
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