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On her daily walk to the scientific station, biologist Miriam San José crouches near a shallow water body surrounded by thick plants and retrieves a compact green sound recorder.

She had placed there through the night to record the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an invasive threat with consequences that scientists are starting to comprehend.

Despite teeming with remarkable wildlife – such as centuries-old large turtles, marine iguanas, and the famous finches that sparked Charles Darwin's evolutionary theory – the island chain off the coast of South America had historically been devoid of frogs and toads.

During the 1990s, this changed. Several tiny amphibians traveled from mainland Ecuador to the islands, likely as stowaways on cargo ships.

DNA research suggest that, through time, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a firm presence on several islands: multiple locations.

The numbers is expanding so quickly that researchers have been finding it difficult to keep track, estimating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the conservation natural reserve.

When the biologist marked frogs and attempted to recapture them in the following week and a half, she could find only a single marked frog occasionally, suggesting their numbers were enormous.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," says San José. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

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

For the scientists, their nocturnal vocalizations are helpful in determining their existence in remote areas, using recorders like the one near San José's workplace.

But nearby farmers say the sounds are so loud they prevent sleep at night.

"In 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, seeing the first frogs in the area," says Larrea Saltos, who started noticing their large numbers about three years ago when one leaped on her palm as she was stepping out of her house.

Environmental Consequences Remains Unclear

The sound isn't the primary problem, though. While the amphibians has been in the islands for almost 30 years, experts still know very little about its impact on the archipelago's delicately balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for invasive species to prosper, as they have none of their enemies. The Galápagos counts 1,645 invasive species, many of which are seriously disrupting the survival of its native ones.

A recent study suggests the non-native frogs are hungry insect consumers, and might be unevenly eating uncommon insects found only on the islands, or depleting the nutrition of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Management Difficulties

The Galápagos frogs have shown some atypical traits, including surviving in brackish water, which is rare for frogs.

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

"We really don't know this part," she says, worried the larvae could be impacting the islands' clean water, a very scarce commodity in the islands.

Techniques to curb the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried collecting significant quantities by manual methods and gradually increasing the salt content of lagoons in vain.

Studies suggests applying coffee – which is highly poisonous to amphibians – or using electrical methods could assist, but these approaches aren't always secure for other uncommon Galápagos organisms.

Without answers to more of the fundamental issues about their biology and impact, culling the frogs might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the increasing use of environmental DNA techniques and genetic analysis will assist her team understand of the invader, funding for the project has been hard to obtain.

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