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During her regular commute to the research facility, scientist the researcher stoops near a small water body covered by thick vegetation and retrieves a compact plastic audio recorder.

The device was left there overnight to record the characteristic croaks of the Fowler's snouted treefrog, known by local researchers as an non-native species with effects that experts are starting to understand.

Despite abounding with remarkable wildlife – including ancient giant tortoises, marine lizards, and the well-known finches that inspired Darwin's theory of evolution – the island chain near the shoreline of Ecuador had historically been devoid of frogs and toads.

In the late 1990s, this changed. Some small tree frogs traveled from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic studies indicate that, through time, there have been multiple unintentional introductions to the archipelago, and the frogs now have a strong presence on two islands: Isabela and Santa Cruz.

The population is growing so rapidly that researchers have been finding it difficult to monitor, calculating populations in the hundreds of thousands on each island, across developed and farming areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to find them in the following week and a half, she could locate just one marked frog from time to time, suggesting their populations were enormous.

They calculated six thousand frogs in a solitary pond. "Our estimates are still very conservative," states San José. "I am pretty sure there are even more."

Deafening Noise and Rising Worries

The amphibians' abundance is evident from the acoustic chaos they cause. "The number of frogs and the noise – it's really incredible," says San José.

For the scientists, their nocturnal vocalizations are useful in determining their existence in far-flung areas, using audio devices like the one outside San José's workplace.

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

"During the wet season, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from Santa Cruz.

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

Environmental Consequences Remains Unclear

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost three decades, scientists still know very little about its impact on the archipelago's delicately balanced terrestrial and aquatic environments.

On islands, it is very common for invasive organisms to thrive, as they have few of their enemies. The islands counts 1,645 invasive types, many of which are significantly affecting the survival of its endemic ones.

A 2020 research suggests the non-native frogs are hungry bug consumers, and might be disproportionately consuming uncommon bugs found exclusively on the archipelago, or depleting the food sources of the region's rare avian species, affecting the food chain.

Unique Characteristics and Control Challenges

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

Their development process is also highly variable, with some tadpoles becoming frogs very quickly and others taking a long time: the researcher witnessed one which remained as a tadpole in her lab for half a year.

"We truly don't know this part," she says, worried the tadpoles could be impacting the islands' clean water, a very scarce commodity in the islands.

Techniques to control the amphibians in the beginning of the century were largely ineffective. Park rangers tried collecting significant quantities by manual methods and slowly raising the salinity of ponds in vain.

Studies indicates applying coffee – which is extremely poisonous to amphibians – or using electrical methods could assist, but these approaches aren't necessarily secure for other uncommon Galápagos organisms.

Without answers to more of the fundamental issues about their lifestyle and effect, culling the amphibians might not even be the right way to advance, says the biologist.

Financial Obstacles for Research

While she hopes the growing use of eDNA methods and DNA examination will help her group make sense of the invader, financial support for the project has been hard to obtain.

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