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During her regular commute to the research facility, biologist Miriam San José stoops near a shallow pond covered by dense plants and retrieves a small plastic audio device.

The device was left there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, known by local scientists as an invasive species with effects that scientists are just beginning to comprehend.

Although abounding with unique wildlife – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the Galápagos archipelago off the coast of South America had historically been devoid of amphibians.

In the late 1990s, this shifted. Some small amphibians traveled from mainland Ecuador to the islands, probably as stowaways on transport vessels.

Genetic studies indicate that, through time, there have been multiple unintentional arrivals to the archipelago, and the amphibians now have a strong presence on two islands: multiple locations.

The population is growing so rapidly that scientists have been struggling to monitor, estimating numbers in the millions on every island, across developed and agricultural areas, but also in the conservation natural reserve.

When San José marked frogs and attempted to recapture them in the following 10 days, she could locate just one marked frog from time to time, indicating their numbers were massive.

They calculated six thousand frogs in a solitary pond. "The calculations are still very conservative," states San José. "I am quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

The frogs' proliferation is clear from the sound disruption they cause. "The amount of frogs and the sound – it's truly insane," says the scientist.

For the researchers, their nightly mating calls are helpful in estimating their presence in far-flung areas, using audio devices like the one near San José's office.

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

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

"At first it was a surprise, seeing the initial frogs in the region," says Larrea Saltos, who started noticing their large numbers about several years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Remains Unknown

The sound isn't the fundamental problem, though. While the species has been in the Galápagos for almost three decades, experts still know limited information about its effect on the islands' precariously balanced land and water ecosystems.

On islands, it is very typical for invasive species to thrive, as they have few of their enemies. The Galápagos counts over sixteen hundred invasive species, many of which are significantly disrupting the safety of its endemic ones.

A 2020 study indicates the non-native frogs are voracious bug consumers, and might be disproportionately eating uncommon bugs found exclusively on the archipelago, or depleting the nutrition of the region's rare birds, disrupting the food chain.

Unusual Traits and Control Challenges

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

Their metamorphosis stage is also highly inconsistent, with some larvae turning into frogs very rapidly and others taking a extended period: the researcher observed one which stayed as a larva in her laboratory for half a year.

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

Techniques to curb the amphibians in the early 2000s were largely unsuccessful. Park rangers tried collecting significant quantities by manual methods and gradually increasing the salt content of ponds in vain.

Research suggests applying caffeine – which is extremely toxic to frogs – or using electrical methods could assist, but these methods aren't necessarily secure for other rare Galápagos organisms.

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

Funding Challenges for Research

While she hopes the growing use of environmental DNA techniques and DNA analysis will assist her group make sense of the invasive species, financial support for the project has been hard to obtain.

"Everyone wants to give support for preserving frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to control."