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During her regular commute to the scientific station, scientist Miriam San José stoops near a small pond covered by thick plants and retrieves a small plastic sound recorder.

The device was left there overnight to record the characteristic calls of the Fowler's snouted treefrog, known by local researchers as an invasive species with effects that experts are starting to comprehend.

Despite teeming with remarkable animals – such as ancient large turtles, marine iguanas, and the well-known finches that inspired Charles Darwin's theory of evolution – the island chain near the coast of South America had long remained devoid of frogs and toads.

During the 1990s, this shifted. Some tiny tree frogs made their way from continental the mainland to the islands, probably as stowaways on cargo ships.

Genetic studies indicate that, over the years, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a firm presence on several locations: Isabela and Santa Cruz.

The population is growing so rapidly that scientists have been finding it difficult to keep track, calculating populations in the millions on each island, across urban and farming areas, but also in the protected Galápagos national park.

When the biologist tagged frogs and attempted to recapture them in the subsequent week and a half, she could find only a single tagged frog from time to time, indicating their populations were massive.

They estimated 6,000 frogs in a single pond. "The calculations are still very low," states the researcher. "I am pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is evident from the sound chaos they create. "The number of frogs and the noise – it's truly insane," comments San José.

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

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

"In the wet season, I regularly hear their croaks and they're really loud," says Jadira Larrea Saltos from the island.

"At first it was a shock, seeing the initial frogs in the region," says the farmer, 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 noise isn't the primary problem, though. While the amphibians has been in the islands for almost 30 years, experts still know limited information about its effect on the islands' delicately balanced terrestrial and aquatic environments.

On islands, it is very common for non-native organisms to prosper, as they have few of their natural predators. The Galápagos counts over sixteen hundred invasive types, many of which are significantly affecting the safety of its endemic ones.

A 2020 research indicates the non-native amphibians are hungry insect eaters, and might be disproportionately eating uncommon insects found only on the islands, or reducing the food sources of the region's uncommon birds, affecting the food chain.

Unique Characteristics and Control Challenges

The island amphibians have shown some unusual characteristics, including living in slightly salty water, which is rare for frogs.

Their metamorphosis process is also extremely inconsistent, with some larvae turning into frogs very quickly and others taking a long time: the researcher observed one which remained as a tadpole in her laboratory for half a year.

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

Methods to curb the frogs in the early 2000s were mostly ineffective. Park rangers tried collecting large numbers by manual methods and slowly increasing the salinity of lagoons in vain.

Studies indicates spraying coffee – which is extremely poisonous to amphibians – or using electrical methods could assist, but these approaches aren't always safe for other rare island species.

Without solutions to more of the basic issues about their lifestyle and impact, removing 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 understand of the invasive species, funding for the project has been hard to come by.

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