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During her daily commute to the scientific station, scientist Miriam San José crouches near a shallow pond covered by thick vegetation and collects a small plastic sound recorder.

She had placed there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, known by Galápagos scientists as an invasive threat with effects that experts are just beginning to understand.

Although teeming with remarkable wildlife – such as centuries-old giant tortoises, swimming iguanas, and the famous birds that inspired Darwin's theory of evolution – the island chain near the coast of Ecuador had long remained devoid of amphibians.

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

DNA studies suggest that, through time, there have been multiple accidental arrivals to the islands, and the frogs now have a strong presence on two locations: Isabela and Santa Cruz.

The population is expanding so quickly that researchers have been finding it difficult to keep track, calculating populations in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected natural reserve.

When San José tagged frogs and attempted to recapture them in the following week and a half, she could locate only a single tagged frog occasionally, indicating their populations were massive.

They estimated six thousand frogs in a single pond. "The calculations are still very low," says San José. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The frogs' proliferation is evident from the sound disruption they cause. "The number of frogs and the noise – it's really insane," comments San José.

For the researchers, their nightly mating calls are useful in estimating their existence in far-flung areas, using audio devices like the one outside San José's workplace.

But nearby agricultural workers say the calls are so loud they keep them up at night.

"During the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, seeing the initial frogs in the region," says the farmer, who started noticing their large numbers about several years ago when one jumped on her palm as she was walking out of her front door.

Environmental Consequences Stays Unknown

The noise isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, experts still know limited information about its effect on the archipelago's delicately balanced land and water environments.

On archipelagos, it is very common for invasive organisms to thrive, as they have few of their enemies. The Galápagos has 1,645 introduced species, many of which are significantly affecting the survival of its native ones.

A recent research suggests the non-native amphibians are voracious insect eaters, and might be unevenly consuming rare insects found only on the archipelago, or reducing the food sources of the region's uncommon avian species, affecting the food chain.

Unusual Traits and Management Difficulties

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

Their metamorphosis stage is also highly inconsistent, with some tadpoles becoming frogs very rapidly and others taking a long time: San José witnessed one which stayed as a tadpole in her laboratory for half a year.

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

Techniques to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing significant quantities by manual methods and slowly raising the salt content of ponds in vain.

Studies suggests spraying caffeine – which is highly poisonous to amphibians – or using electrical methods could help, but these approaches aren't necessarily secure for other rare island organisms.

Lacking solutions to more of the fundamental questions about their biology and effect, removing the frogs might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

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

"Everyone wants to give support for preserving frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."