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During her daily walk to the scientific station, scientist Miriam San José crouches near a shallow pond covered by thick vegetation and collects a small green audio device.

She had placed there through the night to capture the characteristic calls of the Fowler's snouted treefrog, known by local researchers as an non-native threat with effects that scientists are just beginning to comprehend.

Although teeming with remarkable wildlife – such as ancient large turtles, marine iguanas, and the famous finches that sparked Darwin's theory of evolution – the Galápagos archipelago near the coast of South America had long remained free of amphibians.

In the late 1990s, this changed. Some small tree frogs made their way from mainland the mainland to the islands, probably as stowaways on transport vessels.

Genetic studies indicate that, through time, there have been repeated unintentional arrivals to the islands, and the amphibians now have a firm foothold on several islands: multiple locations.

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

When San José tagged frogs and attempted to recapture them in the following 10 days, she could locate only a single marked frog from time to time, suggesting their populations were massive.

They estimated six thousand frogs in a single pond. "Our estimates are still very low," says the researcher. "I'm quite certain there are even more."

Deafening Noise and Growing Concerns

The amphibians' proliferation is evident from the acoustic chaos they create. "The number of frogs and the noise – it's truly incredible," comments San José.

For the scientists, their nocturnal mating calls are helpful in determining their presence in remote areas, using audio devices like the one near the office.

But local farmers say the calls are so loud they prevent sleep at night.

"In the wet season, I constantly hear their calls and they're extremely loud," says Jadira Larrea Saltos from the island.

"At first it was a surprise, observing the initial frogs in the area," 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.

Ecological Impact Remains Unknown

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

On archipelagos, it is very typical for non-native species to thrive, as they have none of their enemies. The islands has over sixteen hundred introduced types, many of which are significantly affecting the safety of its endemic ones.

A recent study indicates the non-native amphibians are voracious bug eaters, and might be unevenly eating uncommon bugs found only on the islands, or reducing the food sources of the region's uncommon birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The island frogs have shown some unusual traits, including surviving in brackish water, which is rare for amphibians.

Their development stage is also extremely variable, with some larvae becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a larva in her lab for half a year.

"We truly don't know this aspect," she says, concerned the tadpoles could be affecting the region's freshwater, a very limited resource in Galápagos.

Techniques to curb the frogs in the early 2000s were largely unsuccessful. Conservation officers tried collecting significant quantities by hand and slowly raising the salinity of ponds in without success.

Research suggests applying caffeine – which is highly poisonous to frogs – or using electrical methods could help, but these approaches aren't always safe for other uncommon island organisms.

Without answers to more of the fundamental issues about their biology and effect, removing the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Research

While she expects the increasing use of environmental DNA techniques and genetic analysis will help her team understand of the invader, financial support for the research has been difficult to come by.

"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."