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On her daily commute to the scientific station, biologist the researcher crouches near a small pond surrounded by thick plants and collects a small green audio recorder.

She had placed there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, known by local scientists as an non-native species with consequences that experts are just beginning to comprehend.

Despite abounding with unique animals – including ancient giant tortoises, marine lizards, and the famous finches that sparked Charles Darwin's evolutionary theory – the island chain off the shoreline of South America had long remained devoid of amphibians.

In the late 1990s, this shifted. Some tiny tree frogs traveled from mainland Ecuador to the islands, probably as stowaways on transport vessels.

DNA research indicate that, over the years, there have been multiple unintentional introductions to the archipelago, and the frogs now have a strong presence on several locations: Isabela and Santa Cruz.

The numbers is expanding so rapidly that scientists have been finding it difficult to monitor, calculating numbers in the hundreds of thousands on every island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When the biologist marked frogs and attempted to find them in the subsequent 10 days, she could find only a single marked frog from time to time, indicating their populations were enormous.

They estimated 6,000 frogs in a single pond. "Our estimates are still very low," says San José. "I am pretty sure there are even more."

Acoustic Chaos and Rising Worries

The frogs' abundance is clear from the acoustic chaos they create. "The number of frogs and the sound – it's really insane," comments the scientist.

For the scientists, their nightly vocalizations are helpful in determining their existence in remote areas, using audio devices like the one near San José's workplace.

But nearby farmers say the sounds are so loud they prevent sleep at night.

"In the wet season, I regularly hear their croaks and they're really loud," says a local coffee farmer from the island.

"Initially it was a shock, seeing the initial frogs in the region," says the farmer, who started observing their large numbers about several years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Stays Unclear

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost 30 years, scientists still know very little about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive species to thrive, as they have none of their natural predators. The Galápagos counts 1,645 introduced types, many of which are significantly disrupting the survival of its endemic ones.

A 2020 research suggests the non-native amphibians are hungry insect consumers, and might be disproportionately consuming rare bugs found only on the islands, or depleting the nutrition of the islands' uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The Galápagos amphibians have shown some atypical traits, including living in slightly salty water, which is rare for frogs.

Their development process is also highly variable, with some larvae turning into frogs very quickly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for half a year.

"We really don't know this part," she says, worried the larvae could be affecting the islands' clean water, a very limited commodity in the islands.

Techniques to control the amphibians in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by manual methods and gradually raising the salinity of ponds in without success.

Research suggests applying coffee – which is highly poisonous to frogs – or using electrocution could help, but these approaches aren't necessarily safe for other uncommon Galápagos species.

Without answers to more of the fundamental issues about their biology and effect, removing the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA methods and DNA analysis will help her group make sense of the invader, funding for the research has been difficult to obtain.

"Everybody wants to give support for protecting frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to control."