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On her daily commute to the research facility, scientist Miriam San José crouches near a shallow water body covered by dense vegetation and retrieves a small green sound recorder.

She had placed there through the night to capture the distinctive calls of the Scinax quinquefasciatus, recognized by local researchers as an non-native species with effects that scientists are starting to comprehend.

Although teeming with unique wildlife – including ancient large turtles, swimming iguanas, and the famous finches that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago near the coast of South America had historically been free of amphibians.

In the late 1990s, this changed. Some tiny tree frogs traveled from mainland the mainland to the islands, probably as stowaways on cargo ships.

DNA research indicate that, over the years, there have been multiple unintentional arrivals to the islands, and the amphibians now have a strong foothold on several islands: Isabela and Santa Cruz.

The population is expanding so rapidly that scientists have been struggling to keep track, calculating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the protected natural reserve.

When San José marked frogs and attempted to find them in the subsequent week and a half, she could find only a single marked frog from time to time, suggesting their populations were massive.

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

Acoustic Chaos and Growing Concerns

The frogs' abundance is clear from the acoustic chaos they cause. "The number of frogs and the sound – it's really incredible," comments the scientist.

For the researchers, their nightly mating calls are helpful in estimating their presence in remote areas, using recorders like the one outside the workplace.

But local agricultural workers say the sounds are so loud they keep them up at night.

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

"At first it was a surprise, observing the initial frogs in the region," says Larrea Saltos, who started noticing their abundance about several years ago when one leaped on her hand as she was walking out of her front door.

Ecological Impact Stays Unknown

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

On islands, it is very common for invasive organisms to prosper, as they have few of their enemies. The islands counts 1,645 introduced species, many of which are seriously disrupting the safety of its endemic ones.

A 2020 research suggests the invasive amphibians are voracious bug consumers, and might be unevenly consuming rare insects found only on the archipelago, or depleting the nutrition of the region's uncommon birds, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

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

Their development process is also highly inconsistent, with some larvae becoming frogs very rapidly and others taking a long time: San José observed one which remained as a larva in her laboratory for half a year.

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

Methods to control the frogs in the beginning of the century were largely ineffective. Conservation officers tried collecting significant quantities by hand and slowly raising the salt content of ponds in without success.

Studies suggests spraying coffee – which is highly poisonous to frogs – or using electrical methods could help, but these methods aren't always secure for other rare Galápagos species.

Lacking solutions to more of the basic questions about their biology and effect, culling the amphibians might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she expects the growing use of environmental DNA methods and DNA examination will help her team understand of the invader, financial support for the project has been difficult to obtain.

"Everybody wants to give funding for preserving frogs," says San José. "But it's harder to find financial backing for an introduced frog that you might want to control."