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On her daily walk to the scientific station, biologist Miriam San José stoops near a shallow water body covered by thick plants and retrieves a compact plastic audio recorder.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native threat with effects that scientists are starting to comprehend.

Although teeming with unique animals – including ancient large turtles, marine lizards, and the famous finches that inspired Charles Darwin's theory of evolution – the island chain near the shoreline of Ecuador had long remained free of amphibians.

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

DNA studies indicate that, over the years, there have been repeated unintentional arrivals to the islands, and the frogs now have a firm foothold on two islands: multiple locations.

The numbers is growing so rapidly that researchers have been struggling to monitor, calculating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the protected Galápagos national park.

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

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

Acoustic Chaos and Rising Worries

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

For the scientists, their nightly mating calls are useful in determining their presence in remote areas, using recorders like the one near San José's workplace.

But local agricultural workers say the sounds are so raucous they keep them up at night.

"During the wet season, I regularly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

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

Environmental Consequences Stays Unclear

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for almost 30 years, experts still know very little about its effect on the islands' precariously balanced land and water ecosystems.

On archipelagos, it is very typical for non-native species to thrive, as they have few of their natural predators. The Galápagos has 1,645 introduced types, many of which are seriously disrupting the survival of its endemic ones.

A recent research suggests the non-native amphibians are hungry insect eaters, and might be unevenly consuming rare bugs found exclusively on the islands, or depleting the food sources of the islands' uncommon birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

The Galápagos amphibians have shown some atypical traits, including living in brackish water, which is uncommon for frogs.

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

"We really don't know this part," she says, worried the tadpoles could be affecting the islands' freshwater, a very scarce commodity in Galápagos.

Methods to control the amphibians in the early 2000s were largely unsuccessful. Park rangers tried collecting large numbers by hand and gradually increasing the salt content of lagoons in without success.

Research indicates applying caffeine – which is extremely toxic to amphibians – or using electrical methods could help, but these approaches aren't always secure for other uncommon Galápagos organisms.

Without answers to more of the fundamental issues about their lifestyle and effect, culling the amphibians might not even be the correct way to proceed, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of eDNA techniques and genetic analysis will help her group make sense of the invasive species, financial support for the project has been hard to obtain.

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