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On her daily walk to the scientific station, scientist Miriam San José crouches near a shallow pond covered by thick plants and retrieves a small plastic sound device.

The device was left there through the night to capture the distinctive calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an non-native species with consequences that scientists are just beginning to understand.

Despite teeming with unique wildlife – including ancient giant tortoises, swimming iguanas, and the famous finches that sparked Charles Darwin's theory of evolution – the island chain off the coast of South America had historically been free of frogs and toads.

During the 1990s, this shifted. Several small amphibians traveled from mainland Ecuador to the archipelago, likely as stowaways on cargo ships.

DNA research suggest that, through time, there have been repeated unintentional arrivals to the islands, and the amphibians now have a firm presence on several locations: multiple locations.

The numbers is expanding so quickly that researchers have been finding it difficult to monitor, estimating populations 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 find only a single tagged frog occasionally, suggesting their populations were enormous.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," says the researcher. "I am quite certain there are additional numbers."

Acoustic Chaos and Growing Concerns

The amphibians' proliferation is evident from the acoustic chaos they create. "The number of frogs and the sound – it's truly incredible," says the scientist.

For the researchers, their nocturnal vocalizations are useful in estimating their presence in far-flung areas, using recorders like the one near the office.

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

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

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

Environmental Consequences Stays Unknown

The noise isn't the primary problem, however. While the species has been in the Galápagos for nearly three decades, experts still know very little about its impact on the archipelago's delicately balanced land and water ecosystems.

On archipelagos, it is very typical for non-native organisms to thrive, as they have few of their natural predators. The islands counts 1,645 introduced types, many of which are seriously affecting the safety of its native ones.

A 2020 study suggests the invasive frogs are hungry insect consumers, and might be unevenly consuming rare insects found only on the archipelago, or depleting the food sources of the islands' rare avian species, affecting the food chain.

Unusual Traits and Management Difficulties

The Galápagos frogs have shown some atypical traits, including surviving in slightly salty water, which is uncommon for amphibians.

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

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

Techniques to control the amphibians in the early 2000s were largely ineffective. Conservation officers tried capturing large numbers by manual methods and slowly increasing the salt content of ponds in vain.

Research suggests applying coffee – which is extremely toxic to amphibians – or using electrical methods could help, but these approaches aren't necessarily safe for other rare Galápagos species.

Without answers to more of the basic questions about their lifestyle and effect, removing the frogs might not even be the right way to proceed, says the biologist.

Funding Challenges for Research

While she expects the growing use of environmental DNA techniques and DNA analysis will assist her group understand of the invader, funding for the project has been hard to come by.

"Everybody wants to give support for preserving frogs," says the researcher. "But it's harder to find financial backing for an invasive frog that you might want to manage."