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On her regular walk to the research facility, biologist the researcher stoops near a shallow pond covered by dense plants and collects a compact green sound recorder.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local researchers as an invasive threat with effects that scientists are starting to understand.

Although teeming with unique wildlife – including ancient large turtles, marine lizards, and the famous birds that inspired Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had long remained free of amphibians.

During the 1990s, this shifted. Some tiny tree frogs traveled from continental Ecuador to the islands, probably as stowaways on transport vessels.

Genetic studies indicate that, over the years, there have been repeated unintentional arrivals to the archipelago, and the frogs now have a strong presence on two locations: multiple locations.

The numbers is growing so quickly that scientists have been finding it difficult to monitor, estimating numbers in the hundreds of thousands on every island, across urban and farming areas, but also in the conservation natural reserve.

When San José tagged amphibians and attempted to recapture them in the subsequent week and a half, she could find just one tagged frog from time to time, indicating their populations were massive.

They estimated 6,000 frogs in a single pond. "Our estimates are still very conservative," says San José. "I am quite certain there are additional numbers."

Deafening Noise and Rising Worries

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

For the scientists, their nocturnal mating calls are useful in determining their presence in remote areas, using audio devices like the one outside San José's office.

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

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

"Initially it was a shock, observing the initial frogs in the area," says the farmer, who started noticing their abundance about several years ago when one jumped on her palm as she was walking out of her front door.

Ecological Impact Stays Unclear

The sound isn't the primary problem, though. While the amphibians has been in the islands for almost 30 years, experts still know very little about its effect on the islands' delicately balanced land and water environments.

On archipelagos, it is very common for non-native species to prosper, as they have none of their enemies. The islands counts over sixteen hundred introduced types, many of which are significantly affecting the safety of its endemic ones.

A 2020 study indicates the non-native amphibians are hungry insect eaters, and might be unevenly eating uncommon insects found only on the archipelago, or depleting the nutrition of the islands' rare avian species, disrupting the food chain.

Unique Characteristics and Control Challenges

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

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 larva in her lab for six months.

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

Techniques to control the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried capturing large numbers by hand and gradually increasing the salt content of ponds in without success.

Research suggests spraying caffeine – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't always secure for other uncommon Galápagos organisms.

Lacking answers to more of the fundamental issues about their biology and effect, removing the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Study

While she hopes the growing use of eDNA methods and genetic examination will help her group make sense of the invader, financial support for the research has been hard to come by.

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