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During her regular commute to the research facility, biologist the researcher crouches near a small water body covered by dense plants and retrieves a small green audio recorder.

She had placed there overnight to record the characteristic calls of the Fowler's snouted treefrog, recognized by local researchers as an non-native species with effects that experts are starting to comprehend.

Despite abounding with unique animals – such as centuries-old giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had long remained free of frogs and toads.

In the late 1990s, this shifted. Some tiny amphibians traveled from mainland Ecuador to the archipelago, probably as hitchhikers on cargo ships.

DNA studies indicate that, over the years, there have been multiple unintentional introductions to the archipelago, and the amphibians now have a firm foothold on two locations: Isabela and Santa Cruz.

The population is expanding so rapidly that researchers have been finding it difficult to keep track, estimating numbers in the millions on each island, across developed and farming areas, but also in the protected Galápagos national park.

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

They estimated six thousand frogs in a single pond. "Our estimates are still very low," says San José. "I am pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The frogs' abundance is clear from the acoustic chaos they cause. "The number of frogs and the sound – it's truly incredible," says the scientist.

For the researchers, their nightly vocalizations are helpful in estimating their existence in far-flung areas, using recorders like the one near the office.

But nearby farmers say the sounds are so raucous they keep them up at night.

"During the rainy period, I constantly hear their calls and they're really loud," says a local coffee farmer from Santa Cruz.

"At first it was a surprise, observing the initial frogs in the area," says the farmer, who started observing their large numbers about several years ago when one leaped on her palm as she was stepping out of her house.

Ecological Impact Stays Unknown

The sound isn't the primary problem, though. While the species has been in the islands for nearly 30 years, experts still know very little about its impact on the islands' precariously balanced land and water ecosystems.

On islands, it is very common for non-native organisms to thrive, as they have none of their natural predators. The islands counts 1,645 invasive species, many of which are significantly affecting the safety of its native ones.

A recent research suggests the invasive frogs are hungry insect eaters, and might be disproportionately consuming uncommon bugs found exclusively on the archipelago, or depleting the food sources of the islands' uncommon birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The Galápagos frogs have exhibited some unusual characteristics, including living in brackish water, which is uncommon for amphibians.

Their metamorphosis process is also highly variable, with some larvae becoming frogs very rapidly and others taking a long time: the researcher observed one which stayed as a larva in her lab for six months.

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

Methods to curb the frogs in the early 2000s were mostly unsuccessful. Conservation officers tried capturing large numbers by manual methods and gradually raising the salinity of ponds in without success.

Studies indicates applying caffeine – which is highly toxic to amphibians – or using electrical methods could help, but these methods aren't always safe for other uncommon island organisms.

Lacking solutions to more of the fundamental issues about their lifestyle and impact, culling the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Study

While she expects the growing use of eDNA techniques and genetic analysis will help her team make sense of the invasive species, funding for the project has been difficult to come by.

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