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During her daily commute to the research facility, biologist Miriam San José crouches near a shallow water body surrounded by thick vegetation and collects a small plastic audio recorder.

She had placed there overnight to capture the characteristic calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive species with consequences that scientists are just beginning to comprehend.

Although teeming with remarkable animals – such as centuries-old large turtles, swimming iguanas, and the well-known birds that inspired Darwin's theory of evolution – the island chain near the shoreline of South America had historically been devoid of amphibians.

During the 1990s, this changed. Some tiny tree frogs traveled from mainland the mainland to the archipelago, probably as stowaways on cargo ships.

DNA research suggest that, through time, there have been multiple unintentional arrivals to the archipelago, and the amphibians now have a firm foothold on several locations: multiple locations.

The population is growing so rapidly that researchers have been struggling to monitor, estimating populations in the millions on each island, across urban and agricultural areas, but also in the protected Galápagos national park.

When the biologist tagged frogs and attempted to recapture them in the subsequent week and a half, she could find only a single tagged frog occasionally, suggesting their numbers were massive.

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very low," states the researcher. "I am pretty sure there are even more."

Deafening Noise and Growing Concerns

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

For the researchers, their nightly vocalizations are useful in determining their existence in far-flung areas, using recorders like the one outside San José's office.

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

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

"Initially it was a shock, observing the first frogs in the region," says the farmer, who started observing their large numbers about three years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Stays Unclear

The noise isn't the primary problem, though. While the amphibians has been in the Galápagos for almost three decades, experts still know limited information about its effect on the islands' precariously balanced land and water environments.

On islands, it is very typical for non-native species to prosper, as they have few of their natural predators. The Galápagos counts over sixteen hundred invasive species, many of which are significantly affecting the survival of its native ones.

A 2020 research suggests the invasive frogs are voracious bug consumers, and might be disproportionately eating uncommon insects found exclusively on the archipelago, or reducing the nutrition of the islands' rare avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island frogs have exhibited some unusual traits, including surviving in brackish water, which is uncommon for amphibians.

Their development stage is also highly inconsistent, with some larvae turning into frogs very quickly and others taking a extended period: the researcher observed one which stayed as a tadpole in her lab for half a year.

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

Techniques to control the frogs in the beginning of the century were largely unsuccessful. Conservation officers tried capturing large numbers by manual methods and slowly raising the salt content of lagoons in without success.

Research indicates applying coffee – which is extremely poisonous to amphibians – or using electrocution could assist, but these approaches aren't necessarily secure for other rare Galápagos species.

Without answers to more of the basic issues about their lifestyle and impact, removing the frogs might not even be the right way to proceed, says San José.

Funding Challenges for Research

While she hopes the increasing use of eDNA techniques and genetic examination will assist her team understand of the invader, funding for the project has been difficult to obtain.

"Everyone wants to give support for preserving frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to manage."