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On her regular commute to the scientific station, biologist Miriam San José crouches near a small pond surrounded by thick plants and collects a compact green sound recorder.

The device was left there overnight to record the distinctive calls of the Fowler's snouted treefrog, recognized by local scientists as an non-native threat with consequences that experts are starting to understand.

Although abounding with remarkable wildlife – including centuries-old giant tortoises, marine iguanas, and the well-known finches that inspired Charles Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been devoid of frogs and toads.

In the late 1990s, this changed. Some small tree frogs made their way from continental Ecuador to the archipelago, probably as stowaways on cargo ships.

DNA research suggest that, over the years, there have been multiple accidental arrivals to the archipelago, and the frogs now have a strong foothold on two locations: multiple locations.

The population is expanding so rapidly that researchers have been finding it difficult to keep track, calculating populations in the millions on each island, across urban and farming areas, but also in the conservation Galápagos national park.

When San José marked amphibians and attempted to recapture them in the following week and a half, she could locate just one tagged frog occasionally, indicating their populations were enormous.

They calculated six thousand frogs in a single pond. "Our estimates are still very low," states San José. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

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

For the scientists, their nocturnal mating calls are helpful in determining their presence in far-flung areas, using recorders like the one outside San José's workplace.

But local farmers say the calls are so raucous they prevent sleep at night.

"During the wet season, I constantly hear their calls 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 abundance about three years ago when one jumped on her hand as she was walking out of her house.

Environmental Consequences Remains Unclear

The noise 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 impact on the islands' delicately balanced land and water ecosystems.

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

A 2020 study indicates the invasive amphibians are voracious bug eaters, and might be unevenly eating uncommon insects found exclusively on the islands, or depleting the food sources of the islands' uncommon avian species, affecting the food chain.

Unique Characteristics and Control Challenges

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

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

"We truly don't know this aspect," she says, worried the larvae could be impacting the region's clean water, a very scarce commodity in Galápagos.

Techniques to control the frogs in the beginning of the century were mostly ineffective. Park rangers tried capturing significant quantities by hand and slowly raising the salinity of ponds in vain.

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

Lacking answers to more of the fundamental issues about their lifestyle and impact, removing the frogs might not even be the right way to advance, says the biologist.

Funding Challenges for Research

While she hopes the growing use of eDNA techniques and DNA examination will help her team understand of the invader, financial support for the research has been hard to obtain.

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