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On her regular walk to the research facility, scientist the researcher crouches near a shallow pond covered by dense vegetation and collects a compact green sound device.

The device was left there through the night to record the characteristic croaks of the Scinax quinquefasciatus, recognized by Galápagos researchers as an invasive species with effects that scientists are starting to comprehend.

Although abounding with remarkable animals – including centuries-old giant tortoises, marine lizards, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had historically been devoid of frogs and toads.

In the late 1990s, this shifted. Some tiny amphibians traveled from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

DNA research suggest that, over the years, there have been repeated accidental arrivals to the islands, and the frogs now have a strong foothold on several islands: multiple locations.

The numbers is growing so rapidly that researchers have been finding it difficult to keep track, calculating populations in the millions on each island, across urban and agricultural areas, but also in the conservation natural reserve.

When the biologist tagged frogs and attempted to recapture them in the following week and a half, she could find just one marked frog from time to time, suggesting their numbers were enormous.

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very low," says the researcher. "I'm pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The frogs' proliferation is clear from the acoustic chaos they cause. "The amount of frogs and the sound – it's truly incredible," says San José.

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

But local farmers say the sounds are so loud they keep them up at night.

"During the wet season, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, observing the initial frogs in the area," says Larrea Saltos, who started observing their abundance about three years ago when one jumped on her palm as she was walking out of her house.

Environmental Consequences Stays Unclear

The noise isn't the primary problem, though. While the species has been in the Galápagos for almost 30 years, experts still know very little about its effect on the islands' delicately balanced terrestrial and aquatic environments.

On islands, it is very typical for non-native species to prosper, as they have few of their enemies. The Galápagos has 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

A 2020 study indicates the invasive frogs are hungry insect consumers, and might be unevenly eating uncommon bugs found only on the islands, or reducing the nutrition of the islands' uncommon avian species, affecting the ecosystem balance.

Unusual Traits and Control Challenges

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

Their development stage is also extremely inconsistent, with some larvae turning into frogs very quickly and others taking a extended period: the researcher observed one which remained as a larva in her lab for half a year.

"We really don't know this aspect," she says, concerned the larvae could be affecting the region's freshwater, a very limited resource in the islands.

Methods to control the frogs in the beginning of the century were mostly ineffective. Conservation officers tried capturing significant quantities by hand and slowly increasing the salt content of lagoons in vain.

Research indicates applying coffee – which is highly poisonous to frogs – or using electrical methods could assist, but these methods aren't necessarily secure for other uncommon Galápagos organisms.

Lacking answers to more of the basic questions about their lifestyle and effect, culling the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Study

While she expects the increasing use of eDNA methods and DNA analysis will help her team understand of the invader, financial support for the project has been hard to come by.

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