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On her daily walk to the scientific station, biologist Miriam San José stoops near a small water body covered by thick plants and collects a small plastic audio device.

The device was left there through the night to record the characteristic calls of the Fowler's snouted treefrog, known by local researchers as an non-native species with effects that experts are just beginning to understand.

Despite teeming with remarkable wildlife – including centuries-old giant tortoises, marine iguanas, and the well-known birds that inspired Charles Darwin's evolutionary theory – the island chain off the shoreline of Ecuador had long remained devoid of frogs and toads.

In the late 1990s, this changed. Several small amphibians made their way from mainland Ecuador to the archipelago, likely as hitchhikers on cargo ships.

DNA research suggest that, through time, there have been multiple accidental introductions to the islands, and the amphibians now have a strong presence on two locations: Isabela and Santa Cruz.

The numbers is expanding so quickly that researchers have been struggling to monitor, calculating populations in the hundreds of thousands on every island, across developed and farming areas, but also in the protected Galápagos national park.

When the biologist marked frogs and attempted to recapture them in the following 10 days, she could find only a single tagged frog occasionally, indicating their numbers were massive.

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

Deafening Noise and Rising Worries

The amphibians' proliferation is evident from the sound chaos they create. "The amount of frogs and the sound – it's really incredible," comments the scientist.

For the researchers, their nocturnal mating calls are helpful in determining their existence in remote areas, using audio devices like the one outside the workplace.

But nearby farmers 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 Jadira Larrea Saltos from the island.

"Initially it was a shock, observing the initial frogs in the region," says the farmer, who started noticing their large numbers about three years ago when one leaped on her palm as she was stepping out of her front door.

Ecological Impact Stays Unclear

The sound isn't the fundamental problem, though. While the species has been in the islands for almost 30 years, scientists still know limited information about its impact on the archipelago's delicately balanced land and water environments.

On islands, it is very typical for non-native organisms to prosper, as they have none of their enemies. The Galápagos has over sixteen hundred introduced species, many of which are significantly disrupting the safety of its endemic ones.

A 2020 research suggests the non-native frogs are voracious bug consumers, and might be unevenly eating rare bugs found exclusively on the islands, or depleting the nutrition of the islands' uncommon avian species, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

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

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

"We truly don't know this part," she says, worried the larvae could be affecting the islands' clean water, a very limited commodity in Galápagos.

Techniques to control the amphibians in the beginning of the century were largely unsuccessful. Conservation officers tried collecting large numbers by manual methods and slowly increasing the salinity of lagoons in vain.

Studies suggests applying caffeine – which is extremely poisonous to amphibians – or using electrical methods could help, but these methods aren't always safe for other rare Galápagos organisms.

Without answers to more of the fundamental questions about their biology and effect, removing the frogs might not even be the correct way to advance, says the biologist.

Financial Obstacles for Study

While she hopes the increasing use of environmental DNA methods and DNA analysis will assist her team understand of the invasive species, financial support for the research has been hard to obtain.

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