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On her regular walk to the research facility, biologist Miriam San José stoops near a shallow water body covered by dense plants and retrieves a small plastic sound device.

She had placed there overnight to record the distinctive calls of the Fowler's snouted treefrog, known by local researchers as an non-native species with effects that experts are starting to understand.

Although abounding with unique animals – including centuries-old large turtles, marine iguanas, and the famous finches that sparked Darwin's theory of evolution – the Galápagos archipelago off the shoreline of Ecuador had historically been free of frogs and toads.

During the 1990s, this changed. Several small tree frogs made their way from continental the mainland to the archipelago, probably as stowaways on cargo ships.

DNA research indicate that, through time, there have been multiple unintentional arrivals to the archipelago, and the frogs now have a strong presence on several islands: multiple locations.

The numbers is expanding so rapidly that scientists have been finding it difficult to monitor, calculating populations in the millions on every island, across developed and agricultural areas, but also in the protected natural reserve.

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

They estimated six thousand frogs in a solitary pond. "The calculations are still very low," says the researcher. "I am pretty sure there are even more."

Acoustic Chaos and Growing Concerns

The amphibians' abundance is evident from the acoustic disruption they cause. "The amount of frogs and the noise – it's really insane," comments San José.

For the scientists, their nocturnal mating calls are useful in determining their presence in remote areas, using audio devices like the one near San José's workplace.

But local agricultural workers say the calls are so loud they prevent sleep at night.

"During the wet season, I regularly hear their calls and they're really loud," says a local coffee farmer from the island.

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

Environmental Consequences Remains Unknown

The sound isn't the primary problem, however. While the species has been in the islands for almost 30 years, experts still know very little about its effect on the islands' delicately balanced terrestrial and aquatic ecosystems.

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

A 2020 research indicates the non-native frogs are voracious insect consumers, and might be unevenly consuming rare bugs found only on the islands, or reducing the nutrition of the region's uncommon avian species, disrupting the food chain.

Unusual Traits and Management Difficulties

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

Their development process is also highly inconsistent, with some larvae turning into frogs very quickly and others taking a long time: San José observed one which stayed as a tadpole in her laboratory for half a year.

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

Methods to curb the amphibians in the beginning of the century were mostly unsuccessful. Park rangers tried collecting significant quantities by hand and slowly increasing the salt content of ponds in vain.

Research suggests applying caffeine – which is highly toxic to frogs – or using electrical methods could help, but these methods aren't necessarily safe for other uncommon island species.

Lacking answers to more of the fundamental questions about their lifestyle and impact, culling the amphibians might not even be the right way to proceed, says the biologist.

Financial Obstacles for Research

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

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