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

She had placed there through the night to record the characteristic croaks of the Fowler's snouted treefrog, recognized by local researchers as an non-native species with consequences that experts are just beginning to comprehend.

Although teeming with unique animals – such as centuries-old giant tortoises, swimming iguanas, and the well-known finches that inspired Darwin's theory of evolution – the Galápagos archipelago off the shoreline of Ecuador had historically been free of amphibians.

In the late 1990s, this changed. Some tiny tree frogs traveled from mainland Ecuador to the islands, likely as hitchhikers on transport vessels.

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

The population is expanding so quickly that scientists have been finding it difficult to keep track, estimating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the protected Galápagos national park.

When San José marked frogs and attempted to recapture them in the subsequent week and a half, she could locate just one tagged frog from time to time, suggesting their numbers were enormous.

They calculated 6,000 frogs in a single pond. "Our estimates are still very conservative," states San José. "I'm quite certain there are additional numbers."

Acoustic Chaos and Rising Worries

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

For the scientists, their nightly vocalizations are helpful in estimating their presence in far-flung areas, using audio devices like the one near the workplace.

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

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

"Initially it was a surprise, observing the initial frogs in the area," says the farmer, who started observing their abundance about three years ago when one leaped on her hand as she was stepping out of her house.

Ecological Impact Stays Unknown

The sound isn't the fundamental problem, though. While the amphibians has been in the Galápagos for almost three decades, scientists still know limited information about its impact on the archipelago's precariously balanced land and water ecosystems.

On islands, it is very typical for invasive organisms to prosper, as they have few of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are significantly affecting the survival of its endemic ones.

A 2020 research suggests the non-native frogs are hungry bug consumers, and might be unevenly consuming rare insects found only on the archipelago, or depleting the food sources of the islands' rare birds, disrupting the food chain.

Unique Characteristics and Management Difficulties

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

Their metamorphosis process is also highly variable, with some larvae turning into frogs very quickly and others taking a long time: San José observed one which remained as a larva in her lab for six months.

"We truly don't know this part," she says, concerned the tadpoles could be affecting the region's clean water, a very scarce resource in Galápagos.

Methods to curb the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried capturing significant quantities by manual methods and slowly increasing the salt content of lagoons in vain.

Studies indicates spraying coffee – which is highly toxic to frogs – or using electrocution could assist, but these approaches aren't necessarily secure for other rare island species.

Lacking solutions to more of the basic issues about their biology and impact, culling the frogs might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she hopes the growing use of environmental DNA techniques and genetic analysis will assist her group understand of the invader, financial support for the project has been difficult to come by.

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