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

She had placed there overnight to capture the characteristic calls of the Fowler's snouted treefrog, recognized by Galápagos scientists as an invasive species with effects that scientists are just beginning to understand.

Although abounding with unique wildlife – including ancient large turtles, swimming lizards, and the well-known finches that inspired Charles Darwin's evolutionary theory – the island chain off the shoreline of South America had historically been free of frogs and toads.

In the late 1990s, this shifted. Several tiny amphibians made their way from mainland the mainland to the islands, likely as stowaways on transport vessels.

Genetic studies indicate that, through time, there have been repeated accidental arrivals to the archipelago, and the frogs now have a strong foothold on two locations: multiple locations.

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

When San José tagged amphibians and attempted to find them in the subsequent week and a half, she could find just one tagged frog from time to time, suggesting their numbers were massive.

They calculated 6,000 frogs in a solitary pond. "Our estimates are still very low," states San José. "I am quite certain there are even more."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is clear from the sound chaos they create. "The number of frogs and the noise – it's truly incredible," comments the scientist.

For the researchers, their nocturnal vocalizations are useful in determining their existence in far-flung areas, using recorders like the one near San José's office.

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

"In the rainy period, I constantly hear their croaks and they're extremely loud," says a local coffee farmer from the island.

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

Ecological Impact Remains Unknown

The sound isn't the primary problem, though. While the amphibians has been in the islands for almost three decades, scientists still know limited information about its effect on the islands' precariously balanced terrestrial and aquatic ecosystems.

On islands, it is very common for invasive organisms to thrive, as they have few of their enemies. The Galápagos counts over sixteen hundred introduced species, many of which are significantly disrupting the safety of its native ones.

A recent study suggests the non-native amphibians are hungry bug consumers, and might be disproportionately eating uncommon insects found exclusively on the archipelago, or reducing the nutrition of the region's uncommon birds, disrupting the ecosystem balance.

Unique Characteristics and Control Challenges

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

Their development process is also extremely inconsistent, with some tadpoles turning into frogs very rapidly and others taking a long time: San José observed one which remained as a tadpole in her laboratory for six months.

"We truly don't know this aspect," she says, concerned the tadpoles could be impacting the region's clean water, a very limited resource in Galápagos.

Techniques to curb the frogs in the beginning of the century were mostly unsuccessful. Park rangers tried capturing significant quantities by hand and gradually increasing the salt content of ponds in vain.

Studies indicates spraying caffeine – which is highly poisonous to amphibians – or using electrocution could assist, but these approaches aren't always secure for other rare Galápagos species.

Lacking answers to more of the fundamental questions about their lifestyle and effect, culling the frogs might not even be the right way to advance, says the biologist.

Funding Challenges for Study

While she expects the increasing use of eDNA techniques and DNA examination will assist her team understand of the invader, financial support for the project has been hard to come by.

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