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During her regular walk to the research facility, biologist Miriam San José stoops near a small water body covered by thick plants and collects a compact plastic audio recorder.

She had placed there through the night to capture the characteristic calls of the Scinax quinquefasciatus, recognized by local researchers as an non-native species with effects that experts are just beginning to comprehend.

Despite abounding with unique wildlife – such as centuries-old large turtles, swimming iguanas, and the famous finches that sparked Darwin's theory of evolution – the island chain off the shoreline of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this shifted. Several small tree frogs made their way from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

Genetic research indicate that, through time, there have been multiple unintentional introductions to the islands, and the amphibians now have a strong presence on two islands: Isabela and Santa Cruz.

The population is growing so quickly that researchers have been struggling to monitor, 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 amphibians and attempted to find them in the following week and a half, she could find just one marked frog occasionally, indicating their numbers were massive.

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

Acoustic Chaos and Growing Concerns

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

For the scientists, their nocturnal mating calls are helpful in determining their presence in far-flung areas, using recorders like the one outside San José's workplace.

But local farmers say the sounds are so loud they keep them up at night.

"During the rainy period, I regularly hear their calls and they're extremely loud," says Jadira Larrea Saltos from Santa Cruz.

"At first it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started observing their large numbers about several years ago when one leaped on her palm as she was stepping out of her front door.

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, though. While the species has been in the islands for nearly three decades, scientists still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for invasive organisms to thrive, as they have few of their enemies. The Galápagos counts over sixteen hundred introduced types, many of which are seriously affecting the safety of its endemic ones.

A recent study suggests the invasive frogs are voracious insect eaters, and might be unevenly eating uncommon insects found only on the archipelago, or reducing the nutrition of the region's uncommon avian species, affecting the food chain.

Unique Characteristics and Control Challenges

The island amphibians have shown some atypical characteristics, including surviving in brackish water, which is rare for amphibians.

Their development process is also extremely inconsistent, with some tadpoles turning into frogs very quickly and others taking a extended period: San José observed one which stayed as a larva in her laboratory for half a year.

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

Methods to curb the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting large numbers by manual methods and gradually raising the salinity of ponds in vain.

Research suggests applying caffeine – which is highly toxic to frogs – or using electrical methods could assist, but these approaches aren't always safe for other rare Galápagos species.

Lacking answers to more of the fundamental questions about their lifestyle and impact, removing the amphibians might not even be the correct way to proceed, says the biologist.

Funding Challenges for Research

While she expects the increasing use of eDNA techniques and genetic analysis will help her team understand of the invader, funding for the research has been hard to come by.

"Everybody wants to give support for protecting frogs," says San José. "But it's harder to find financial backing for an invasive frog that you might want to control."