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During her regular walk to the research facility, scientist Miriam San José crouches near a shallow pond covered by thick plants and retrieves a small plastic audio recorder.

She had placed there overnight to capture the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive threat with consequences that scientists are starting to understand.

Despite abounding with unique animals – including ancient large turtles, marine lizards, and the well-known finches that sparked Darwin's evolutionary theory – the island chain near the shoreline of South America had long remained devoid of frogs and toads.

During the 1990s, this shifted. Several small amphibians made their way from mainland the mainland to the islands, probably as stowaways on transport vessels.

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

The population is expanding so quickly that scientists have been struggling to keep track, calculating numbers in the hundreds of thousands on every island, across urban and farming areas, but also in the protected natural reserve.

When the biologist tagged amphibians and attempted to recapture them in the subsequent week and a half, she could locate just one marked frog from time to time, indicating their populations were massive.

They estimated six thousand frogs in a single pond. "Our estimates are still very conservative," states the researcher. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

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

For the researchers, their nocturnal mating calls are helpful in estimating their presence in far-flung areas, using recorders like the one outside the office.

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

"In the rainy period, I regularly hear their calls and they're extremely loud," says a local coffee farmer from the island.

"At first it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started noticing their large numbers 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 fundamental problem, though. While the species has been in the Galápagos for nearly 30 years, experts still know very little about its impact on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very typical for invasive organisms to prosper, as they have none of their natural predators. The islands counts 1,645 invasive types, many of which are seriously disrupting the safety of its endemic ones.

A recent research indicates the non-native amphibians are hungry bug consumers, and might be disproportionately consuming uncommon insects found exclusively on the archipelago, or depleting the nutrition of the islands' rare avian species, disrupting the food chain.

Unusual Traits and Control Challenges

The Galápagos frogs have exhibited some atypical traits, including surviving in slightly salty water, which is rare for amphibians.

Their development stage is also extremely variable, with some larvae turning into frogs very quickly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for six months.

"We really don't know this part," she says, concerned the larvae could be impacting the islands' freshwater, a very limited resource in Galápagos.

Methods to control the amphibians in the beginning of the century were largely ineffective. Park rangers tried collecting significant quantities by hand and gradually raising the salinity of lagoons in vain.

Research suggests spraying coffee – which is extremely toxic to amphibians – or using electrocution could help, but these methods aren't necessarily safe for other uncommon Galápagos species.

Lacking solutions to more of the basic questions about their biology and effect, removing the amphibians might not even be the correct way to advance, says the biologist.

Funding Challenges for Study

While she expects the growing use of environmental DNA techniques and DNA analysis will assist her team make sense of the invader, financial support for the research has been hard to come by.

"Everybody wants to give funding for preserving frogs," says San José. "But it's harder to find funding for an invasive frog that you might want to control."