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During her regular walk to the scientific station, biologist the researcher stoops near a small water body surrounded by dense vegetation and retrieves a small plastic sound recorder.

The device was left there through the night to capture the characteristic croaks of the Scinax quinquefasciatus, known by Galápagos scientists as an non-native species with consequences that scientists are starting to comprehend.

Although teeming with remarkable wildlife – such as ancient large turtles, marine iguanas, and the famous birds that sparked Darwin's theory of evolution – the island chain off the shoreline of Ecuador had long remained devoid of frogs and toads.

During the 1990s, this shifted. Some small amphibians made their way from mainland Ecuador to the islands, probably as hitchhikers on transport vessels.

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

The population is growing so quickly that scientists have been finding it difficult to monitor, calculating populations in the millions on every island, across urban and agricultural areas, but also in the conservation natural reserve.

When the biologist tagged frogs and attempted to find them in the following 10 days, she could find just one tagged frog occasionally, indicating their numbers were massive.

They estimated six thousand frogs in a single pond. "Our estimates are still very conservative," says the researcher. "I'm pretty sure there are even more."

Acoustic Chaos and Rising Worries

The amphibians' proliferation is evident from the sound disruption they cause. "The number of frogs and the noise – it's really incredible," says San José.

For the researchers, their nightly vocalizations are useful in determining their presence in remote areas, using audio devices like the one outside the workplace.

But nearby farmers say the sounds are so raucous they prevent sleep at night.

"In 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 region," says the farmer, who started observing their abundance about several years ago when one jumped on her hand as she was walking out of her house.

Ecological Impact Remains Unknown

The noise isn't the primary problem, however. While the amphibians has been in the Galápagos for almost three decades, scientists still know very little about its impact on the islands' delicately balanced terrestrial and aquatic environments.

On archipelagos, it is very typical for non-native species to prosper, as they have few of their natural predators. The Galápagos has over sixteen hundred invasive species, many of which are significantly affecting the survival of its native ones.

A recent study suggests the non-native amphibians are voracious insect eaters, and might be unevenly consuming uncommon bugs found only on the archipelago, or reducing the nutrition of the islands' rare birds, disrupting the food chain.

Unusual Traits and Management Difficulties

The island amphibians have shown some atypical characteristics, including living in brackish water, which is uncommon for frogs.

Their development process is also extremely variable, with some larvae becoming frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a larva in her laboratory for six months.

"We really don't know this part," she says, concerned the tadpoles could be affecting the region's clean water, a very limited commodity in Galápagos.

Methods to curb the frogs in the beginning of the century were largely ineffective. Conservation officers tried collecting significant quantities by hand and gradually increasing the salinity of lagoons in without success.

Research indicates spraying caffeine – which is highly toxic to frogs – or using electrical methods could assist, but these approaches aren't always safe for other uncommon Galápagos species.

Without solutions to more of the fundamental issues about their lifestyle and effect, removing the frogs might not even be the correct way to advance, says San José.

Funding Challenges for Study

While she hopes the increasing use of eDNA techniques and genetic analysis will assist her group understand of the invasive species, funding for the research has been hard to come by.

"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 manage."