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During her daily walk to the research facility, scientist the researcher crouches near a shallow pond covered by dense vegetation and collects a compact plastic sound device.

The device was left there overnight to capture the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an invasive species with consequences that experts are just beginning to understand.

Although teeming with remarkable animals – such as centuries-old giant tortoises, marine iguanas, and the well-known birds that inspired Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had long remained devoid of amphibians.

During the 1990s, this changed. Some tiny tree frogs traveled from continental Ecuador to the islands, likely as hitchhikers on transport vessels.

Genetic research indicate that, over the years, there have been multiple accidental arrivals to the islands, and the frogs now have a strong foothold on several locations: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been struggling to monitor, estimating populations in the hundreds of thousands on each island, across urban and agricultural areas, but also in the conservation natural reserve.

When San José tagged amphibians and attempted to recapture them in the subsequent week and a half, she could find only a single marked frog occasionally, suggesting their numbers were enormous.

They estimated six thousand frogs in a single pond. "Our estimates are still very conservative," states San José. "I am quite certain there are additional numbers."

Deafening Noise and Rising Worries

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

For the researchers, their nightly vocalizations are useful in determining their presence in remote areas, using audio devices like the one near San José's workplace.

But local agricultural workers say the sounds are so loud they prevent sleep at night.

"In the wet season, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, seeing the first frogs in the region," says Larrea Saltos, who started observing their abundance about three years ago when one jumped on her hand as she was walking out of her house.

Environmental Consequences Remains Unclear

The sound isn't the primary problem, however. While the species has been in the Galápagos for almost three decades, experts still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for invasive species to thrive, as they have none of their natural predators. The islands has 1,645 invasive types, many of which are significantly affecting the safety of its endemic ones.

A recent research indicates the non-native frogs are voracious insect consumers, and might be disproportionately eating uncommon bugs found only on the archipelago, or depleting the food sources of the region's uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

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

Their metamorphosis process is also extremely variable, with some larvae turning into frogs very quickly and others taking a extended period: the researcher observed one which remained as a tadpole in her laboratory for six months.

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

Methods to curb the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by hand and slowly increasing the salt content of lagoons in vain.

Studies suggests spraying caffeine – which is highly poisonous to amphibians – or using electrical methods could help, but these methods aren't necessarily safe for other rare island species.

Without answers to more of the fundamental issues about their biology and impact, culling the amphibians might not even be the right way to proceed, says the biologist.

Funding Challenges for Study

While she expects the growing use of environmental DNA techniques and genetic analysis will assist her team make sense of the invader, funding for the project has been difficult to obtain.

"Everybody wants to give support for protecting frogs," says the researcher. "But it's more difficult to find financial backing for an introduced frog that you might want to control."