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During her daily walk to the scientific station, biologist Miriam San José stoops near a small water body surrounded by dense plants and collects a compact green audio device.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with consequences that scientists are starting to understand.

Despite abounding with unique animals – including centuries-old giant tortoises, swimming lizards, and the well-known finches that sparked Darwin's evolutionary theory – the island chain near the coast of South America had historically been free of amphibians.

In the late 1990s, this changed. Some small tree frogs traveled from continental the mainland to the islands, probably as stowaways on cargo ships.

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

The population is growing so rapidly that researchers have been finding it difficult to monitor, calculating numbers in the millions on each island, across urban and farming areas, but also in the protected Galápagos national park.

When the biologist tagged amphibians and attempted to find them in the following 10 days, she could find only a single marked frog from time to time, indicating their numbers were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very low," says the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

The amphibians' proliferation is clear from the sound chaos they cause. "The amount of frogs and the noise – it's truly insane," says San José.

For the researchers, their nocturnal vocalizations are helpful in determining their presence in remote areas, using recorders like the one near the office.

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

"During the rainy period, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.

"Initially it was a shock, observing the initial 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 walking out of her house.

Environmental Consequences Remains Unknown

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

On islands, it is very common for non-native organisms to thrive, as they have none of their enemies. The islands has 1,645 introduced species, many of which are significantly disrupting the safety of its native ones.

A recent research suggests the non-native frogs are voracious bug consumers, and might be disproportionately consuming rare bugs found only on the archipelago, or depleting the nutrition of the region's rare avian species, affecting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their development process is also extremely variable, with some larvae becoming frogs very quickly and others taking a extended period: the researcher observed one which remained as a tadpole in her lab for six months.

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

Techniques to control the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried capturing large numbers by hand and gradually increasing the salt content of lagoons in without success.

Studies suggests spraying coffee – which is extremely poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily secure for other uncommon island organisms.

Lacking solutions to more of the fundamental questions about their biology and effect, culling the frogs might not even be the correct way to advance, says San José.

Funding Challenges for Research

While she expects the growing use of environmental DNA methods and DNA analysis will assist her team understand of the invasive species, funding for the research has been difficult to obtain.

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