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On her daily commute to the research facility, scientist Miriam San José stoops near a small water body covered by thick vegetation and retrieves a compact green sound recorder.

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

Although teeming with unique animals – such as centuries-old giant tortoises, marine iguanas, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain off the coast of Ecuador had historically been devoid of amphibians.

During the 1990s, this shifted. Some tiny amphibians made their way from continental Ecuador to the archipelago, likely as stowaways on cargo ships.

DNA research indicate that, over the years, there have been repeated accidental arrivals to the islands, and the frogs now have a firm foothold on several islands: multiple locations.

The numbers is expanding so rapidly that researchers have been struggling to keep track, estimating populations in the hundreds of thousands on each island, across urban and agricultural areas, but also in the protected natural reserve.

When the biologist tagged amphibians and attempted to recapture them in the following 10 days, she could locate just one marked frog occasionally, suggesting their numbers were enormous.

They estimated six thousand frogs in a single pond. "Our estimates are still very low," says the researcher. "I am quite certain there are even more."

Acoustic Chaos and Growing Concerns

The frogs' abundance is evident from the sound disruption they cause. "The number of frogs and the sound – it's really incredible," says the scientist.

For the scientists, their nocturnal mating calls are helpful in estimating their existence in far-flung areas, using recorders like the one near the office.

But local agricultural workers say the sounds are so loud they keep them up at night.

"During the wet season, I constantly hear their croaks and they're really loud," says Jadira Larrea Saltos from Santa Cruz.

"Initially it was a surprise, observing the first frogs in the area," says Larrea Saltos, who started observing their large numbers about several years ago when one jumped on her hand as she was walking out of her front door.

Environmental Consequences Remains Unclear

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

On islands, it is very common for invasive species to thrive, as they have none of their natural predators. The Galápagos has over sixteen hundred invasive species, many of which are seriously affecting the survival of its endemic ones.

A recent research indicates the invasive frogs are hungry bug eaters, and might be unevenly eating rare bugs found only on the islands, or reducing the food sources of the region's uncommon birds, disrupting the food chain.

Unusual Traits and Control Challenges

The island amphibians have exhibited some unusual traits, including living in brackish water, which is uncommon for amphibians.

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

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

Methods to curb the amphibians in the early 2000s were largely ineffective. Park rangers tried capturing significant quantities by manual methods and gradually raising the salt content of lagoons in without success.

Research suggests spraying coffee – which is extremely poisonous to amphibians – or using electrocution could assist, but these methods aren't necessarily safe for other uncommon island species.

Lacking answers to more of the fundamental questions about their biology and effect, removing the amphibians might not even be the right way to advance, says San José.

Financial Obstacles for Study

While she hopes the growing use of environmental DNA techniques and DNA examination will assist her group make sense of the invader, funding for the research has been hard to come by.

"Everyone wants to give support for protecting frogs," says San José. "But it's more difficult to find financial backing for an introduced frog that you might want to control."