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During her regular walk to the research facility, biologist the researcher crouches near a shallow water body covered by dense vegetation and retrieves a compact green sound device.

She had placed there overnight to capture the characteristic calls of the Fowler's snouted treefrog, known by Galápagos researchers as an non-native threat with effects that experts are starting to understand.

Although teeming with remarkable animals – including centuries-old large turtles, marine lizards, and the well-known birds that inspired Darwin's evolutionary theory – the island chain off the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Several small tree frogs made their way from continental the mainland to the archipelago, likely as hitchhikers on transport vessels.

DNA research suggest that, through time, there have been multiple accidental arrivals to the archipelago, and the frogs now have a strong foothold on several islands: Isabela and Santa Cruz.

The numbers is growing so rapidly that scientists have been finding it difficult to keep track, calculating numbers in the millions on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When San José marked amphibians and attempted to recapture them in the following week and a half, she could locate just one tagged frog occasionally, suggesting their populations were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very low," says San José. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the sound chaos they cause. "The number of frogs and the sound – it's really incredible," comments the scientist.

For the scientists, their nightly vocalizations are helpful in estimating their presence in remote areas, using audio devices like the one near the office.

But local agricultural workers say the sounds are so loud they prevent sleep at night.

"During the wet season, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a shock, seeing the first frogs in the region," says Larrea Saltos, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unclear

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for almost three decades, scientists still know very little about its effect on the archipelago's delicately balanced terrestrial and aquatic environments.

On islands, it is very common for invasive organisms to thrive, as they have few of their natural predators. The islands counts 1,645 invasive species, many of which are significantly affecting the safety of its endemic ones.

A 2020 study indicates the non-native frogs are hungry insect eaters, and might be disproportionately eating uncommon insects found exclusively on the archipelago, or depleting the nutrition of the region's uncommon avian species, disrupting the food chain.

Unusual Traits and Management Difficulties

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

Their metamorphosis process is also highly inconsistent, with some larvae turning into frogs very rapidly and others taking a long time: San José observed one which stayed as a larva in her lab for six months.

"We really don't know this part," she says, concerned the tadpoles could be affecting the islands' clean water, a very limited resource in Galápagos.

Methods to control the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried capturing large numbers by hand and gradually increasing the salinity of ponds in vain.

Research indicates applying caffeine – which is extremely poisonous to amphibians – or using electrical methods could help, but these methods aren't necessarily secure for other uncommon Galápagos organisms.

Lacking solutions to more of the fundamental issues about their biology and effect, culling the frogs might not even be the correct way to proceed, says San José.

Financial Obstacles for Study

While she hopes the increasing use of eDNA techniques and genetic examination will assist her team understand of the invasive species, financial support for the project has been difficult to come by.

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