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On her regular walk to the scientific station, scientist Miriam San José stoops near a small pond covered by thick vegetation and retrieves a small green audio device.

The device was left there through the night to capture the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos scientists as an invasive species with consequences that scientists are just beginning to understand.

Although abounding with remarkable wildlife – such as ancient large turtles, swimming lizards, and the well-known birds that inspired Darwin's evolutionary theory – the Galápagos archipelago off the coast of Ecuador had historically been free of amphibians.

During the 1990s, this changed. Several tiny amphibians traveled from continental the mainland to the islands, probably as stowaways on transport vessels.

Genetic research suggest that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a strong foothold on several locations: Isabela and Santa Cruz.

The numbers is growing so quickly that researchers have been struggling to keep track, calculating populations in the millions on every island, across urban and agricultural areas, but also in the conservation natural reserve.

When the biologist marked amphibians and attempted to find them in the following 10 days, she could find only a single tagged frog from time to time, suggesting their populations were enormous.

They calculated six thousand frogs in a solitary pond. "The calculations are still very low," states San José. "I'm pretty sure there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is clear from the sound chaos they create. "The number of frogs and the noise – it's truly incredible," says San José.

For the scientists, their nocturnal mating calls are useful in estimating their presence in remote areas, using recorders like the one near the office.

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

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

"Initially it was a surprise, seeing the first frogs in the region," 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 house.

Ecological Impact Remains Unknown

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for nearly three decades, scientists still know very little about its effect on the islands' precariously balanced terrestrial and aquatic environments.

On islands, it is very typical for non-native organisms to thrive, as they have none of their natural predators. The Galápagos has over sixteen hundred invasive types, many of which are seriously disrupting the safety of its endemic ones.

A 2020 research suggests the non-native frogs are voracious insect eaters, and might be unevenly eating rare bugs found exclusively on the archipelago, or reducing the food sources of the region's rare birds, disrupting the food chain.

Unusual Traits and Control Challenges

The Galápagos frogs have exhibited some atypical characteristics, including surviving in slightly salty water, which is rare for frogs.

Their metamorphosis stage is also extremely variable, with some tadpoles becoming frogs very rapidly and others taking a long time: San José observed one which remained as a larva in her lab for half a year.

"We really don't know this aspect," she says, worried the larvae could be affecting the region's freshwater, a very scarce resource in Galápagos.

Techniques to control the frogs in the beginning of the century were mostly ineffective. Conservation officers tried capturing significant quantities by hand and gradually increasing the salt content of lagoons in vain.

Research suggests spraying caffeine – which is highly poisonous to amphibians – or using electrical methods could help, but these approaches aren't always safe for other rare Galápagos organisms.

Lacking answers to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she hopes the increasing use of eDNA methods and DNA analysis will assist her team make sense of the invasive species, funding for the project has been difficult to come by.

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