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During her daily walk to the research facility, biologist the researcher stoops near a small pond covered by thick vegetation and retrieves a compact green audio recorder.

She had placed there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an invasive species with effects that scientists are just beginning to comprehend.

Despite teeming with unique wildlife – such as ancient giant tortoises, swimming iguanas, and the famous birds that sparked Darwin's evolutionary theory – the Galápagos archipelago off the coast of South America had long remained devoid of amphibians.

In the late 1990s, this changed. Several tiny amphibians made their way from mainland Ecuador to the islands, probably as hitchhikers on cargo ships.

Genetic studies suggest that, over the years, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a strong foothold on two locations: Isabela and Santa Cruz.

The numbers is growing so rapidly that researchers have been struggling to monitor, calculating numbers 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 recapture them in the following 10 days, she could find just one tagged frog occasionally, indicating their populations were massive.

They calculated 6,000 frogs in a solitary pond. "The calculations are still very conservative," states San José. "I am pretty sure there are even more."

Deafening Noise and Rising Worries

The frogs' proliferation is evident from the acoustic chaos they create. "The amount of frogs and the sound – it's really incredible," comments San José.

For the researchers, their nightly vocalizations are helpful in estimating their presence in remote areas, using audio devices like the one outside San José's office.

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

"In the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

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

Ecological Impact Stays Unclear

The noise isn't the fundamental problem, however. While the amphibians has been in the Galápagos for nearly 30 years, experts still know very little about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for non-native species to prosper, as they have few of their natural predators. The Galápagos has over sixteen hundred introduced species, many of which are seriously affecting the safety of its native ones.

A recent study suggests the invasive frogs are hungry bug eaters, and might be unevenly consuming uncommon bugs found exclusively on the islands, or reducing the nutrition of the region's uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Management Difficulties

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

Their metamorphosis stage is also extremely inconsistent, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher observed one which remained as a tadpole in her lab for six months.

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

Techniques to curb the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by manual methods and gradually increasing the salt content of ponds in vain.

Studies indicates applying caffeine – which is extremely toxic to amphibians – or using electrocution could help, but these approaches aren't always secure for other rare island organisms.

Without answers to more of the basic issues about their biology and impact, culling 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 eDNA methods and DNA analysis will assist her team understand of the invasive species, funding for the research has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find funding for an introduced frog that you might want to manage."