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During her daily commute to the scientific station, biologist Miriam San José crouches near a small pond covered by thick plants and retrieves a small green sound device.

She had placed there overnight to record the characteristic calls of the Fowler's snouted treefrog, known by local scientists as an invasive species with consequences that experts are just beginning to understand.

Although abounding with remarkable wildlife – including ancient giant tortoises, marine lizards, and the famous birds that inspired Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had long remained devoid of amphibians.

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

Genetic research suggest that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a firm presence on several locations: multiple locations.

The population is expanding so quickly that scientists have been struggling to monitor, calculating populations in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected Galápagos national park.

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

They calculated six thousand frogs in a single pond. "Our estimates are still very low," says San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the acoustic chaos they create. "The amount of frogs and the sound – it's really incredible," comments San José.

For the scientists, their nightly vocalizations are useful in determining their presence in far-flung areas, using audio devices like the one outside San José's workplace.

But nearby agricultural workers say the sounds are so raucous they keep them up at night.

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

"At first it was a shock, observing the first frogs in the area," says the farmer, who started noticing their abundance about three years ago when one leaped on her hand as she was walking out of her house.

Environmental Consequences Stays Unclear

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for almost 30 years, scientists still know very little about its impact on the archipelago's delicately balanced land and water environments.

On archipelagos, it is very typical for non-native species to thrive, as they have few of their natural predators. The Galápagos counts over sixteen hundred invasive species, many of which are significantly disrupting the safety of its native ones.

A 2020 study suggests the invasive amphibians are voracious insect eaters, and might be disproportionately eating rare insects found exclusively on the archipelago, or depleting the nutrition of the region's rare birds, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island frogs have exhibited some unusual characteristics, including living in slightly salty water, which is uncommon for frogs.

Their metamorphosis stage is also highly variable, with some tadpoles turning into frogs very quickly and others taking a long time: San José observed one which stayed as a larva in her laboratory for half a year.

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

Techniques to curb the amphibians in the beginning of the century were largely unsuccessful. Park rangers tried capturing significant quantities by manual methods and gradually increasing the salinity of lagoons in vain.

Research suggests spraying coffee – which is extremely poisonous to amphibians – or using electrical methods could assist, but these methods aren't always safe for other rare Galápagos species.

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

Financial Obstacles for Study

While she hopes the growing use of environmental DNA techniques and DNA examination will help her team make sense of the invader, funding for the research has been hard to obtain.

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