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During her regular commute to the scientific station, biologist the researcher stoops near a small water body surrounded by thick vegetation and collects a small plastic audio recorder.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an invasive species with consequences that scientists are just beginning to understand.

Although teeming with remarkable animals – such as centuries-old giant tortoises, marine iguanas, and the famous birds that sparked Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had historically been devoid of amphibians.

During the 1990s, this changed. Some small tree frogs traveled from continental Ecuador to the islands, probably as stowaways on cargo ships.

Genetic research 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: multiple locations.

The population is expanding so quickly that researchers have been struggling to monitor, calculating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to recapture them in the following week and a half, she could find just one tagged frog occasionally, suggesting their numbers were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," states the researcher. "I'm quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the acoustic chaos they create. "The amount of frogs and the sound – it's truly insane," comments San José.

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

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

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

"Initially it was a shock, seeing the first frogs in the area," says Larrea Saltos, who started observing their abundance about several years ago when one leaped on her hand as she was stepping out of her front door.

Ecological Impact Remains Unknown

The noise isn't the primary problem, though. While the amphibians has been in the islands for nearly three decades, 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 species to prosper, as they have none of their enemies. The islands counts over sixteen hundred invasive species, many of which are significantly disrupting the survival of its endemic ones.

A 2020 study suggests the non-native frogs are voracious bug consumers, and might be unevenly consuming rare bugs found only on the archipelago, or depleting the nutrition of the region's uncommon birds, affecting the food chain.

Unusual Traits and Control Challenges

The island frogs have exhibited some unusual characteristics, including surviving in slightly salty water, which is uncommon for frogs.

Their development stage is also highly variable, with some tadpoles becoming frogs very quickly and others taking a extended period: San José observed one which stayed as a larva in her lab for half a year.

"We truly don't know this part," she says, worried the tadpoles could be affecting the islands' clean water, a very limited resource in Galápagos.

Techniques to curb the amphibians in the beginning of the century were mostly unsuccessful. Conservation officers tried capturing large numbers by manual methods and slowly increasing the salt content of lagoons in without success.

Studies suggests applying caffeine – which is highly poisonous to amphibians – or using electrical methods could assist, but these methods aren't always secure for other uncommon Galápagos species.

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

Funding Challenges for Study

While she expects the growing use of eDNA techniques and DNA examination will assist her team make sense of the invasive species, financial support for the research has been difficult to obtain.

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