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On her daily walk to the research facility, biologist the researcher crouches near a shallow pond covered by dense plants and collects a compact green audio device.

She had placed there through the night to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an invasive species with effects that scientists are starting to understand.

Although teeming with remarkable animals – such as ancient large turtles, swimming iguanas, and the famous birds that inspired Charles Darwin's evolutionary theory – the island chain near the coast of Ecuador had historically been devoid of frogs and toads.

During the 1990s, this shifted. Some tiny tree frogs made their way from mainland the mainland to the archipelago, likely as stowaways on transport vessels.

Genetic research indicate that, through time, there have been multiple unintentional arrivals to the islands, and the frogs now have a firm foothold on several locations: multiple locations.

The numbers is expanding so rapidly that scientists have been struggling to keep track, calculating numbers in the hundreds of thousands on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When the biologist marked frogs and attempted to recapture them in the following 10 days, she could locate only a single marked frog occasionally, indicating their populations were enormous.

They calculated six thousand frogs in a single pond. "The calculations are still very conservative," states San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

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

For the scientists, their nocturnal vocalizations are helpful in determining their presence in far-flung areas, using audio devices like the one near the workplace.

But nearby farmers say the calls 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 Santa Cruz.

"Initially it was a shock, seeing the initial frogs in the area," says the farmer, who started noticing their large numbers about three years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Stays Unclear

The noise isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly 30 years, experts still know limited information about its effect on the archipelago's delicately balanced land and water ecosystems.

On islands, it is very typical for invasive species to prosper, as they have few of their enemies. The islands has 1,645 invasive types, many of which are significantly disrupting the survival of its native ones.

A recent research indicates the non-native frogs are voracious insect consumers, and might be disproportionately consuming uncommon insects found only on the archipelago, or reducing the nutrition of the islands' rare birds, disrupting the ecosystem balance.

Unique Characteristics and Management Difficulties

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

Their metamorphosis process is also extremely inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: San José observed one which stayed as a larva in her laboratory for six months.

"We truly don't know this aspect," she says, worried the larvae could be impacting the region's clean water, a very limited resource in Galápagos.

Methods to curb the frogs in the beginning of the century were mostly unsuccessful. Conservation officers tried collecting large numbers by manual methods and slowly raising the salinity of ponds in without success.

Research suggests spraying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these approaches aren't always safe for other rare island species.

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

Funding Challenges for Study

While she expects the growing use of environmental DNA methods and DNA analysis will help her group make sense of the invader, funding for the research has been hard to obtain.

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