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On her daily walk to the research facility, scientist Miriam San José crouches near a small water body covered by thick plants and retrieves a small plastic sound recorder.

The device was left there overnight to capture the characteristic croaks of the Scinax quinquefasciatus, known by local scientists as an invasive species with effects that scientists are just beginning to comprehend.

Despite abounding with remarkable wildlife – such as ancient giant tortoises, marine lizards, and the well-known birds that sparked Darwin's evolutionary theory – the island chain near the shoreline of South America had historically been devoid of frogs and toads.

In the late 1990s, this shifted. Several small amphibians made their way from mainland the mainland to the archipelago, likely as hitchhikers on transport vessels.

Genetic studies indicate that, over the years, there have been multiple accidental introductions to the archipelago, and the amphibians now have a strong presence on several islands: multiple locations.

The numbers is growing so quickly that researchers have been struggling to monitor, calculating populations in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected Galápagos national park.

When the biologist marked amphibians and attempted to recapture them in the following 10 days, she could find only a single marked frog occasionally, indicating their populations were enormous.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," states San José. "I am pretty sure there are additional numbers."

Acoustic Chaos and Rising Worries

The amphibians' abundance is clear from the sound disruption they create. "The amount of frogs and the sound – it's truly incredible," comments the scientist.

For the scientists, their nocturnal mating calls are helpful in determining their existence in far-flung areas, using recorders like the one near San José's office.

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

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

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

Ecological Impact Remains Unclear

The noise isn't the fundamental problem, though. While the species has been in the Galápagos for nearly three decades, experts still know limited information about its impact on the archipelago's delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very common for non-native species to prosper, as they have few of their natural predators. The islands has 1,645 introduced types, many of which are significantly disrupting the safety of its endemic ones.

A 2020 research indicates the non-native amphibians are hungry bug consumers, and might be disproportionately consuming rare bugs found exclusively on the archipelago, or depleting the food sources of the islands' rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island amphibians have exhibited some atypical characteristics, including living in brackish water, which is uncommon for amphibians.

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

"We truly don't know this aspect," she says, concerned the larvae could be impacting the region's clean water, a very limited resource in the islands.

Methods to control the frogs in the early 2000s were largely unsuccessful. Conservation officers tried capturing large numbers by hand and gradually raising the salinity of ponds in without success.

Studies suggests spraying caffeine – which is extremely toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily safe for other uncommon Galápagos species.

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

Financial Obstacles for Research

While she expects the increasing 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 come by.

"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."