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On her regular walk to the scientific station, biologist Miriam San José crouches near a shallow water body surrounded by thick vegetation and retrieves a small plastic audio device.

The device was left there through the night to record the distinctive croaks of the Fowler's snouted treefrog, recognized by local scientists as an non-native species with effects that scientists are just beginning to comprehend.

Despite teeming with remarkable animals – including ancient large turtles, marine lizards, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had historically been free of frogs and toads.

In the late 1990s, this shifted. Some tiny amphibians made their way from mainland the mainland to the archipelago, likely as hitchhikers on cargo ships.

Genetic research suggest that, through time, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a strong foothold on several locations: multiple locations.

The numbers is expanding so quickly that scientists have been struggling to keep track, estimating populations in the millions on each island, across developed and agricultural areas, but also in the conservation natural reserve.

When San José tagged frogs and attempted to find them in the subsequent week and a half, she could find only a single marked frog from time to time, suggesting their numbers were massive.

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

Deafening Noise and Growing Concerns

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

For the scientists, their nightly mating calls are useful in determining their existence in far-flung areas, using audio devices like the one outside the office.

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

"During the wet season, I regularly hear their calls 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 area," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was walking out of her house.

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, however. While the species has been in the islands for nearly three decades, scientists still know very little about its effect on the islands' delicately balanced land and water ecosystems.

On islands, it is very typical for non-native species to prosper, as they have none of their natural predators. The islands has over sixteen hundred invasive species, many of which are significantly affecting the survival of its endemic ones.

A recent study indicates the non-native amphibians are voracious bug consumers, and might be unevenly eating rare bugs found only on the islands, or depleting the nutrition of the islands' uncommon avian species, affecting the food chain.

Unusual Traits and Control Challenges

The island amphibians have shown some unusual characteristics, including surviving in slightly salty water, which is uncommon for frogs.

Their metamorphosis stage is also highly variable, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher observed one which remained as a tadpole in her laboratory for half a year.

"We truly don't know this part," she says, worried the larvae could be affecting the region's freshwater, a very limited commodity in Galápagos.

Techniques to curb the amphibians in the early 2000s were largely ineffective. Conservation officers tried capturing significant quantities by hand and gradually increasing the salt content of lagoons in without success.

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

Without answers to more of the basic questions about their biology and effect, culling the amphibians might not even be the right way to proceed, says the biologist.

Financial Obstacles for Research

While she expects the growing use of environmental DNA techniques and DNA analysis will help her team understand of the invader, funding for the project has been hard to obtain.

"Everyone wants to give support for preserving frogs," says San José. "But it's more difficult to find funding for an invasive frog that you might want to manage."