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On her daily commute to the research facility, biologist Miriam San José stoops near a shallow water body surrounded by dense vegetation and collects a compact plastic audio recorder.

The device was left there through the night to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos researchers as an non-native threat with effects that scientists are just beginning to understand.

Despite teeming with unique animals – such as ancient large turtles, swimming lizards, and the well-known birds that sparked Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained devoid of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from mainland Ecuador to the archipelago, likely as hitchhikers on cargo ships.

Genetic research indicate that, over the years, there have been multiple unintentional arrivals to the islands, and the amphibians now have a firm presence on several locations: multiple locations.

The numbers is growing so quickly that researchers have been finding it difficult to monitor, estimating numbers in the hundreds of thousands on each island, across developed and farming areas, but also in the protected natural reserve.

When San José tagged amphibians and attempted to find them in the following 10 days, she could find only a single tagged frog occasionally, indicating their populations were massive.

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

Acoustic Chaos and Growing Concerns

The frogs' abundance is clear from the acoustic disruption they cause. "The amount of frogs and the sound – it's really insane," comments the scientist.

For the researchers, their nightly mating calls are helpful in estimating their presence in remote areas, using audio devices like the one near San José's office.

But local farmers say the calls are so raucous they keep them up at night.

"In the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

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

Environmental Consequences Stays Unclear

The sound isn't the fundamental problem, though. While the species has been in the Galápagos for nearly three decades, scientists still know very little about its effect on the islands' delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very common for invasive organisms to prosper, as they have few of their enemies. The islands counts 1,645 introduced species, many of which are significantly disrupting the safety of its endemic ones.

A 2020 study indicates the invasive amphibians are hungry bug eaters, and might be unevenly eating uncommon bugs found exclusively on the archipelago, or depleting the food sources of the islands' rare avian species, disrupting the food chain.

Unusual Traits and Control Challenges

The island amphibians have shown some atypical traits, including living in slightly salty water, which is uncommon for amphibians.

Their metamorphosis stage is also extremely inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: San José witnessed one which remained as a tadpole in her lab for six months.

"We truly don't know this part," she says, worried the tadpoles could be affecting the region's freshwater, a very scarce commodity in the islands.

Techniques to curb the amphibians in the beginning of the century were mostly unsuccessful. Conservation officers tried capturing large numbers by manual methods and gradually raising the salt content of ponds in without success.

Research suggests spraying caffeine – which is highly poisonous to amphibians – or using electrical methods could help, but these methods aren't necessarily secure for other uncommon Galápagos species.

Without solutions to more of the basic questions about their biology and effect, removing the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she expects the increasing use of environmental DNA methods and DNA examination will help her group understand of the invader, financial support for the research has been hard to come by.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to manage."