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On her daily walk to the scientific station, biologist the researcher crouches near a small water body covered by dense vegetation and collects a compact plastic audio device.

She had placed there overnight to record the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos researchers as an non-native threat with effects that experts are starting to comprehend.

Although abounding with remarkable wildlife – such as centuries-old large turtles, marine iguanas, and the well-known birds that sparked Charles Darwin's evolutionary theory – the island chain near the coast of South America had historically been devoid of frogs and toads.

In the late 1990s, this shifted. Some small tree frogs made their way from continental the mainland to the archipelago, probably as hitchhikers on cargo ships.

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

The numbers is growing so rapidly that researchers have been finding it difficult to keep track, calculating populations in the millions on every island, across developed and agricultural areas, but also in the conservation natural reserve.

When San José marked amphibians and attempted to find them in the following 10 days, she could locate only a single tagged frog occasionally, indicating their numbers were massive.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the acoustic chaos they cause. "The number of frogs and the sound – it's truly incredible," comments the scientist.

For the scientists, their nocturnal mating calls are helpful in determining their presence in remote areas, using audio devices like the one outside San José's office.

But nearby agricultural workers say the calls are so loud they prevent sleep at night.

"During the rainy period, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

"Initially it was a shock, observing the initial frogs in the region," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her hand as she was walking out of her front door.

Ecological Impact Stays Unknown

The noise isn't the primary problem, though. While the species has been in the islands for almost three decades, experts still know limited information about its effect on the islands' delicately balanced terrestrial and aquatic environments.

On islands, it is very typical for invasive organisms to prosper, as they have none of their natural predators. The islands counts over sixteen hundred invasive types, many of which are seriously disrupting the survival of its native ones.

A recent research indicates the non-native amphibians are hungry insect eaters, and might be unevenly eating uncommon insects found only on the islands, or reducing the food sources of the islands' uncommon avian species, disrupting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis process is also extremely inconsistent, with some larvae becoming frogs very quickly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory for six months.

"We really don't know this aspect," she says, concerned the tadpoles could be affecting the region's clean water, a very scarce commodity in the islands.

Methods to curb the amphibians in the early 2000s were mostly ineffective. Park rangers tried collecting large numbers by hand and slowly raising the salt content of lagoons in vain.

Studies indicates spraying coffee – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't always safe for other rare island species.

Without answers to more of the basic questions about their biology and effect, culling the frogs might not even be the correct way to advance, says San José.

Funding Challenges for Study

While she expects the increasing use of environmental DNA methods and genetic analysis will assist her team understand of the invader, funding for the project has been hard to obtain.

"Everyone wants to give funding for protecting frogs," says the researcher. "But it's harder to find funding for an introduced frog that you might want to control."