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On her daily commute to the scientific station, scientist Miriam San José crouches near a shallow pond covered by thick plants and collects a compact green sound recorder.

She had placed there through the night to capture the characteristic croaks of the Fowler's snouted treefrog, recognized by Galápagos researchers as an invasive threat with effects that experts are just beginning to understand.

Despite abounding with remarkable animals – including centuries-old giant tortoises, swimming lizards, and the famous birds that sparked Charles Darwin's theory of evolution – the Galápagos archipelago near the shoreline of Ecuador had historically been free of frogs and toads.

During the 1990s, this changed. Some tiny tree frogs made their way from continental Ecuador to the islands, likely as hitchhikers on cargo ships.

Genetic studies suggest that, over the years, there have been multiple accidental arrivals to the archipelago, and the frogs now have a firm presence on several islands: multiple locations.

The population is expanding so quickly that researchers have been finding it difficult to keep track, estimating populations in the millions on each island, across developed and farming areas, but also in the protected natural reserve.

When San José tagged amphibians and attempted to recapture them in the following 10 days, she could find only a single tagged frog from time to time, indicating their numbers were massive.

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

Deafening Noise and Rising Worries

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

For the scientists, their nocturnal 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 sounds are so raucous they keep them up at night.

"In the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.

"Initially it was a surprise, seeing the initial frogs in the region," says the farmer, who started noticing their abundance about three years ago when one leaped on her hand as she was walking out of her front door.

Environmental Consequences Stays Unclear

The noise isn't the primary problem, however. While the species has been in the islands for nearly three decades, experts still know limited information about its effect on the archipelago's precariously balanced terrestrial and aquatic ecosystems.

On archipelagos, it is very typical for invasive species to prosper, as they have few of their natural predators. The Galápagos counts 1,645 introduced species, many of which are significantly disrupting the safety of its native ones.

A 2020 study indicates the non-native frogs are hungry insect eaters, and might be unevenly consuming rare bugs found exclusively on the archipelago, or depleting the nutrition of the islands' rare birds, affecting the ecosystem balance.

Unique Characteristics and Management Difficulties

The island frogs have exhibited some atypical traits, including living in slightly salty water, which is rare for frogs.

Their development stage is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: San José observed one which stayed as a tadpole in her lab for six months.

"We really don't know this aspect," she says, worried the tadpoles could be impacting the islands' freshwater, a very limited resource in Galápagos.

Techniques to curb the amphibians in the early 2000s were mostly ineffective. Park rangers tried capturing significant quantities by hand and gradually raising the salt content of lagoons in without success.

Studies suggests spraying coffee – which is extremely toxic to frogs – or using electrical methods could assist, but these approaches aren't always secure for other rare Galápagos species.

Lacking answers to more of the basic issues about their biology and effect, culling the amphibians might not even be the correct way to proceed, says the biologist.

Funding Challenges for Research

While she expects the increasing use of environmental DNA methods and genetic analysis will help her group make sense of the invader, funding for the project has been hard to obtain.

"Everybody wants to give funding for protecting frogs," says the researcher. "But it's more difficult to find funding for an introduced frog that you might want to manage."