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On her daily walk to the research facility, biologist the researcher stoops near a shallow pond surrounded by thick vegetation and collects a compact green audio device.

She had placed there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native species with consequences that scientists are just beginning to understand.

Despite teeming with unique animals – including centuries-old giant tortoises, swimming lizards, and the famous finches that sparked Charles Darwin's evolutionary theory – the island chain near the coast of South America had long remained devoid of amphibians.

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

Genetic research indicate that, through time, there have been multiple accidental introductions to the archipelago, and the frogs now have a firm presence on two locations: Isabela and Santa Cruz.

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

When the biologist marked frogs and attempted to recapture them in the following week and a half, she could find only a single tagged frog from time to time, suggesting their populations were enormous.

They estimated 6,000 frogs in a single pond. "The calculations are still very low," says San José. "I'm pretty sure there are even more."

Deafening Noise and Rising Worries

The frogs' abundance is clear from the sound chaos they cause. "The amount of frogs and the noise – it's really insane," comments San José.

For the researchers, their nocturnal vocalizations are useful in estimating their existence in remote areas, using audio devices like the one near the workplace.

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

"During the wet season, I constantly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started observing their large numbers about three years ago when one jumped on her palm as she was walking out of her house.

Ecological Impact Stays Unknown

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its impact on the archipelago's precariously balanced land and water ecosystems.

On archipelagos, it is very common for invasive organisms to thrive, as they have none of their enemies. The islands has 1,645 introduced species, many of which are significantly disrupting the survival of its endemic ones.

A 2020 study suggests the invasive amphibians are voracious bug eaters, and might be disproportionately consuming uncommon bugs found exclusively on the islands, or reducing the food sources of the region's uncommon birds, affecting the food chain.

Unusual Traits and Management Difficulties

The island frogs have shown some unusual traits, including living in brackish water, which is rare for frogs.

Their metamorphosis stage is also extremely inconsistent, 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 laboratory for six months.

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

Techniques to control the frogs in the early 2000s were mostly ineffective. Park rangers tried capturing large numbers by manual methods and slowly raising the salt content of ponds in vain.

Research suggests spraying coffee – which is highly toxic to frogs – or using electrical methods could help, but these approaches aren't necessarily secure for other rare Galápagos organisms.

Without solutions to more of the fundamental questions about their lifestyle and impact, culling the frogs might not even be the right way to proceed, says San José.

Funding Challenges for Study

While she hopes the increasing use of environmental DNA methods and DNA examination will help her team make sense of the invader, funding for the research has been difficult to obtain.

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